LinuxLists.cc - [PATCH v8 00/11] tracing/user

2023-02-21 21:11:54

Subject: [PATCH v8 00/11] tracing/user_events: Remote write ABI

2023-02-21 21:11:57

Subject: [PATCH v8 02/11] tracing/user_events: Track fork/exec/exit for mm lifetime

During tracefs discussions it was decided instead of requiring a mapping
within a user-process to track the lifetime of memory descriptors we
should hook the appropriate calls. Do this by adding the minimal stubs
required for task fork, exec, and exit. Currently this is just a NOP.
Future patches will implement these calls fully.

Suggested-by: Mathieu Desnoyers <[email protected]>
Signed-off-by: Beau Belgrave <[email protected]>
---
fs/exec.c | 2 ++
include/linux/sched.h | 5 +++++
include/linux/user_events.h | 18 ++++++++++++++++++
kernel/exit.c | 2 ++
kernel/fork.c | 2 ++
5 files changed, 29 insertions(+)

diff --git a/fs/exec.c b/fs/exec.c
index ab913243a367..d1c83e0dbae5 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -65,6 +65,7 @@
#include <linux/syscall_user_dispatch.h>
#include <linux/coredump.h>
#include <linux/time_namespace.h>
+#include <linux/user_events.h>

#include <linux/uaccess.h>
#include <asm/mmu_context.h>
@@ -1856,6 +1857,7 @@ static int bprm_execve(struct linux_binprm *bprm,
current->fs->in_exec = 0;
current->in_execve = 0;
rseq_execve(current);
+ user_events_execve(current);
acct_update_integrals(current);
task_numa_free(current, false);
return retval;
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 853d08f7562b..a8e683b4291c 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -69,6 +69,7 @@ struct sighand_struct;
struct signal_struct;
struct task_delay_info;
struct task_group;
+struct user_event_mm;

/*
* Task state bitmask. NOTE! These bits are also
@@ -1522,6 +1523,10 @@ struct task_struct {
union rv_task_monitor rv[RV_PER_TASK_MONITORS];
#endif

+#ifdef CONFIG_USER_EVENTS
+ struct user_event_mm *user_event_mm;
+#endif
+
/*
* New fields for task_struct should be added above here, so that
* they are included in the randomized portion of task_struct.
diff --git a/include/linux/user_events.h b/include/linux/user_events.h
index 13689589d36e..3d747c45d2fa 100644
--- a/include/linux/user_events.h
+++ b/include/linux/user_events.h
@@ -11,4 +11,22 @@

#include <uapi/linux/user_events.h>

+#ifdef CONFIG_USER_EVENTS
+struct user_event_mm {
+};
+#endif
+
+static inline void user_events_fork(struct task_struct *t,
+ unsigned long clone_flags)
+{
+}
+
+static inline void user_events_execve(struct task_struct *t)
+{
+}
+
+static inline void user_events_exit(struct task_struct *t)
+{
+}
+
#endif /* _LINUX_USER_EVENTS_H */
diff --git a/kernel/exit.c b/kernel/exit.c
index 15dc2ec80c46..e2aaaa81b281 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -68,6 +68,7 @@
#include <linux/kprobes.h>
#include <linux/rethook.h>
#include <linux/sysfs.h>
+#include <linux/user_events.h>

#include <linux/uaccess.h>
#include <asm/unistd.h>
@@ -816,6 +817,7 @@ void __noreturn do_exit(long code)

coredump_task_exit(tsk);
ptrace_event(PTRACE_EVENT_EXIT, code);
+ user_events_exit(tsk);

validate_creds_for_do_exit(tsk);

diff --git a/kernel/fork.c b/kernel/fork.c
index 9f7fe3541897..180f6d86fbad 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -97,6 +97,7 @@
#include <linux/io_uring.h>
#include <linux/bpf.h>
#include <linux/stackprotector.h>
+#include <linux/user_events.h>

#include <asm/pgalloc.h>
#include <linux/uaccess.h>
@@ -2502,6 +2503,7 @@ static __latent_entropy struct task_struct *copy_process(

trace_task_newtask(p, clone_flags);
uprobe_copy_process(p, clone_flags);
+ user_events_fork(p, clone_flags);

copy_oom_score_adj(clone_flags, p);

--
2.25.1

2023-02-21 21:12:01

by Beau Belgrave

[permalink] [raw]

Subject: [PATCH v8 01/11] tracing/user_events: Split header into uapi and kernel

The UAPI parts need to be split out from the kernel parts of user_events
now that other parts of the kernel will reference it. Do so by moving
the existing include/linux/user_events.h into
include/uapi/linux/user_events.h.

Signed-off-by: Beau Belgrave <[email protected]>
---
include/linux/user_events.h | 52 ++++----------------------------
include/uapi/linux/user_events.h | 48 +++++++++++++++++++++++++++++
kernel/trace/trace_events_user.c | 5 ---
3 files changed, 54 insertions(+), 51 deletions(-)
create mode 100644 include/uapi/linux/user_events.h

diff --git a/include/linux/user_events.h b/include/linux/user_events.h
index 592a3fbed98e..13689589d36e 100644
--- a/include/linux/user_events.h
+++ b/include/linux/user_events.h
@@ -1,54 +1,14 @@
-/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/* SPDX-License-Identifier: GPL-2.0-only */
/*
- * Copyright (c) 2021, Microsoft Corporation.
+ * Copyright (c) 2022, Microsoft Corporation.
*
* Authors:
* Beau Belgrave <[email protected]>
*/
-#ifndef _UAPI_LINUX_USER_EVENTS_H
-#define _UAPI_LINUX_USER_EVENTS_H

-#include <linux/types.h>
-#include <linux/ioctl.h>
+#ifndef _LINUX_USER_EVENTS_H
+#define _LINUX_USER_EVENTS_H

-#ifdef __KERNEL__
-#include <linux/uio.h>
-#else
-#include <sys/uio.h>
-#endif
+#include <uapi/linux/user_events.h>

-#define USER_EVENTS_SYSTEM "user_events"
-#define USER_EVENTS_PREFIX "u:"
-
-/* Create dynamic location entry within a 32-bit value */
-#define DYN_LOC(offset, size) ((size) << 16 | (offset))
-
-/*
- * Describes an event registration and stores the results of the registration.
- * This structure is passed to the DIAG_IOCSREG ioctl, callers at a minimum
- * must set the size and name_args before invocation.
- */
-struct user_reg {
-
- /* Input: Size of the user_reg structure being used */
- __u32 size;
-
- /* Input: Pointer to string with event name, description and flags */
- __u64 name_args;
-
- /* Output: Bitwise index of the event within the status page */
- __u32 status_bit;
-
- /* Output: Index of the event to use when writing data */
- __u32 write_index;
-} __attribute__((__packed__));
-
-#define DIAG_IOC_MAGIC '*'
-
-/* Requests to register a user_event */
-#define DIAG_IOCSREG _IOWR(DIAG_IOC_MAGIC, 0, struct user_reg*)
-
-/* Requests to delete a user_event */
-#define DIAG_IOCSDEL _IOW(DIAG_IOC_MAGIC, 1, char*)
-
-#endif /* _UAPI_LINUX_USER_EVENTS_H */
+#endif /* _LINUX_USER_EVENTS_H */
diff --git a/include/uapi/linux/user_events.h b/include/uapi/linux/user_events.h
new file mode 100644
index 000000000000..03f92366068d
--- /dev/null
+++ b/include/uapi/linux/user_events.h
@@ -0,0 +1,48 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Copyright (c) 2021-2022, Microsoft Corporation.
+ *
+ * Authors:
+ * Beau Belgrave <[email protected]>
+ */
+#ifndef _UAPI_LINUX_USER_EVENTS_H
+#define _UAPI_LINUX_USER_EVENTS_H
+
+#include <linux/types.h>
+#include <linux/ioctl.h>
+
+#define USER_EVENTS_SYSTEM "user_events"
+#define USER_EVENTS_PREFIX "u:"
+
+/* Create dynamic location entry within a 32-bit value */
+#define DYN_LOC(offset, size) ((size) << 16 | (offset))
+
+/*
+ * Describes an event registration and stores the results of the registration.
+ * This structure is passed to the DIAG_IOCSREG ioctl, callers at a minimum
+ * must set the size and name_args before invocation.
+ */
+struct user_reg {
+
+ /* Input: Size of the user_reg structure being used */
+ __u32 size;
+
+ /* Input: Pointer to string with event name, description and flags */
+ __u64 name_args;
+
+ /* Output: Bitwise index of the event within the status page */
+ __u32 status_bit;
+
+ /* Output: Index of the event to use when writing data */
+ __u32 write_index;
+} __attribute__((__packed__));
+
+#define DIAG_IOC_MAGIC '*'
+
+/* Request to register a user_event */
+#define DIAG_IOCSREG _IOWR(DIAG_IOC_MAGIC, 0, struct user_reg *)
+
+/* Request to delete a user_event */
+#define DIAG_IOCSDEL _IOW(DIAG_IOC_MAGIC, 1, char *)
+
+#endif /* _UAPI_LINUX_USER_EVENTS_H */
diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index 908e8a13c675..070551480747 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -19,12 +19,7 @@
#include <linux/tracefs.h>
#include <linux/types.h>
#include <linux/uaccess.h>
-/* Reminder to move to uapi when everything works */
-#ifdef CONFIG_COMPILE_TEST
#include <linux/user_events.h>
-#else
-#include <uapi/linux/user_events.h>
-#endif
#include "trace.h"
#include "trace_dynevent.h"

--
2.25.1

2023-02-21 21:12:03

by Beau Belgrave

[permalink] [raw]

Subject: [PATCH v8 04/11] tracing/user_events: Fixup enable faults asyncly

When events are enabled within the various tracing facilities, such as
ftrace/perf, the event_mutex is held. As events are enabled pages are
accessed. We do not want page faults to occur under this lock. Instead
queue the fault to a workqueue to be handled in a process context safe
way without the lock.

The enable address is marked faulting while the async fault-in occurs.
This ensures that we don't attempt to fault-in more than is necessary.
Once the page has been faulted in, an address write is re-attempted.
If the page couldn't fault-in, then we wait until the next time the
event is enabled to prevent any potential infinite loops.

Signed-off-by: Beau Belgrave <[email protected]>
---
kernel/trace/trace_events_user.c | 120 +++++++++++++++++++++++++++++--
1 file changed, 114 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index 553a82ee7aeb..86bda1660536 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -99,9 +99,23 @@ struct user_event_enabler {
/* Bits 0-5 are for the bit to update upon enable/disable (0-63 allowed) */
#define ENABLE_VAL_BIT_MASK 0x3F

+/* Bit 6 is for faulting status of enablement */
+#define ENABLE_VAL_FAULTING_BIT 6
+
/* Only duplicate the bit value */
#define ENABLE_VAL_DUP_MASK ENABLE_VAL_BIT_MASK

+#define ENABLE_BITOPS(e) ((unsigned long *)&(e)->values)
+
+/* Used for asynchronous faulting in of pages */
+struct user_event_enabler_fault {
+ struct work_struct work;
+ struct user_event_mm *mm;
+ struct user_event_enabler *enabler;
+};
+
+static struct kmem_cache *fault_cache;
+
/* Global list of memory descriptors using user_events */
static LIST_HEAD(user_event_mms);
static DEFINE_SPINLOCK(user_event_mms_lock);
@@ -263,7 +277,85 @@ static int user_event_mm_fault_in(struct user_event_mm *mm, unsigned long uaddr)
}

static int user_event_enabler_write(struct user_event_mm *mm,
- struct user_event_enabler *enabler)
+ struct user_event_enabler *enabler,
+ bool fixup_fault);
+
+static void user_event_enabler_fault_fixup(struct work_struct *work)
+{
+ struct user_event_enabler_fault *fault = container_of(
+ work, struct user_event_enabler_fault, work);
+ struct user_event_enabler *enabler = fault->enabler;
+ struct user_event_mm *mm = fault->mm;
+ unsigned long uaddr = enabler->addr;
+ int ret;
+
+ ret = user_event_mm_fault_in(mm, uaddr);
+
+ if (ret && ret != -ENOENT) {
+ struct user_event *user = enabler->event;
+
+ pr_warn("user_events: Fault for mm: 0x%pK @ 0x%llx event: %s\n",
+ mm->mm, (unsigned long long)uaddr, EVENT_NAME(user));
+ }
+
+ /* Prevent state changes from racing */
+ mutex_lock(&event_mutex);
+
+ /*
+ * If we managed to get the page, re-issue the write. We do not
+ * want to get into a possible infinite loop, which is why we only
+ * attempt again directly if the page came in. If we couldn't get
+ * the page here, then we will try again the next time the event is
+ * enabled/disabled.
+ */
+ clear_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler));
+
+ if (!ret) {
+ mmap_read_lock(mm->mm);
+ user_event_enabler_write(mm, enabler, true);
+ mmap_read_unlock(mm->mm);
+ }
+
+ mutex_unlock(&event_mutex);
+
+ /* In all cases we no longer need the mm or fault */
+ user_event_mm_put(mm);
+ kmem_cache_free(fault_cache, fault);
+}
+
+static bool user_event_enabler_queue_fault(struct user_event_mm *mm,
+ struct user_event_enabler *enabler)
+{
+ struct user_event_enabler_fault *fault;
+
+ fault = kmem_cache_zalloc(fault_cache, GFP_NOWAIT | __GFP_NOWARN);
+
+ if (!fault)
+ return false;
+
+ INIT_WORK(&fault->work, user_event_enabler_fault_fixup);
+ fault->mm = user_event_mm_get(mm);
+ fault->enabler = enabler;
+
+ /* Don't try to queue in again while we have a pending fault */
+ set_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler));
+
+ if (!schedule_work(&fault->work)) {
+ /* Allow another attempt later */
+ clear_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler));
+
+ user_event_mm_put(mm);
+ kmem_cache_free(fault_cache, fault);
+
+ return false;
+ }
+
+ return true;
+}
+
+static int user_event_enabler_write(struct user_event_mm *mm,
+ struct user_event_enabler *enabler,
+ bool fixup_fault)
{
unsigned long uaddr = enabler->addr;
unsigned long *ptr;
@@ -278,11 +370,19 @@ static int user_event_enabler_write(struct user_event_mm *mm,
if (refcount_read(&mm->tasks) == 0)
return -ENOENT;

+ if (unlikely(test_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler))))
+ return -EBUSY;
+
ret = pin_user_pages_remote(mm->mm, uaddr, 1, FOLL_WRITE | FOLL_NOFAULT,
&page, NULL, NULL);

- if (ret <= 0) {
- pr_warn("user_events: Enable write failed\n");
+ if (unlikely(ret <= 0)) {
+ if (!fixup_fault)
+ return -EFAULT;
+
+ if (!user_event_enabler_queue_fault(mm, enabler))
+ pr_warn("user_events: Unable to queue fault handler\n");
+
return -EFAULT;
}

@@ -314,7 +414,7 @@ static void user_event_enabler_update(struct user_event *user)

list_for_each_entry_rcu(enabler, &mm->enablers, link)
if (enabler->event == user)
- user_event_enabler_write(mm, enabler);
+ user_event_enabler_write(mm, enabler, true);

rcu_read_unlock();
mmap_read_unlock(mm->mm);
@@ -562,7 +662,7 @@ static struct user_event_enabler

/* Attempt to reflect the current state within the process */
mmap_read_lock(user_mm->mm);
- *write_result = user_event_enabler_write(user_mm, enabler);
+ *write_result = user_event_enabler_write(user_mm, enabler, false);
mmap_read_unlock(user_mm->mm);

/*
@@ -2201,16 +2301,24 @@ static int __init trace_events_user_init(void)
{
int ret;

+ fault_cache = KMEM_CACHE(user_event_enabler_fault, 0);
+
+ if (!fault_cache)
+ return -ENOMEM;
+
init_group = user_event_group_create(&init_user_ns);

- if (!init_group)
+ if (!init_group) {
+ kmem_cache_destroy(fault_cache);
return -ENOMEM;
+ }

ret = create_user_tracefs();

if (ret) {
pr_warn("user_events could not register with tracefs\n");
user_event_group_destroy(init_group);
+ kmem_cache_destroy(fault_cache);
init_group = NULL;
return ret;
}
--
2.25.1

2023-02-21 21:12:05

by Beau Belgrave

[permalink] [raw]

Subject: [PATCH v8 05/11] tracing/user_events: Add ioctl for disabling addresses

Enablements are now tracked by the lifetime of the task/mm. User
processes need to be able to disable their addresses if tracing is
requested to be turned off. Before unmapping the page would suffice.
However, we now need a stronger contract. Add an ioctl to enable this.

A new flag bit is added, freeing, to user_event_enabler to ensure that
if the event is attempted to be removed while a fault is being handled
that the remove is delayed until after the fault is reattempted.

Signed-off-by: Beau Belgrave <[email protected]>
---
include/uapi/linux/user_events.h | 24 +++++++++
kernel/trace/trace_events_user.c | 93 +++++++++++++++++++++++++++++++-
2 files changed, 115 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/user_events.h b/include/uapi/linux/user_events.h
index 22521bc622db..3e7275e3234a 100644
--- a/include/uapi/linux/user_events.h
+++ b/include/uapi/linux/user_events.h
@@ -46,6 +46,27 @@ struct user_reg {
__u32 write_index;
} __attribute__((__packed__));

+/*
+ * Describes an event unregister, callers must set the size, address and bit.
+ * This structure is passed to the DIAG_IOCSUNREG ioctl to disable bit updates.
+ */
+struct user_unreg {
+ /* Input: Size of the user_unreg structure being used */
+ __u32 size;
+
+ /* Input: Bit to unregister */
+ __u8 disable_bit;
+
+ /* Input: Reserved, set to 0 */
+ __u8 __reserved;
+
+ /* Input: Reserved, set to 0 */
+ __u16 __reserved2;
+
+ /* Input: Address to unregister */
+ __u64 disable_addr;
+} __attribute__((__packed__));
+
#define DIAG_IOC_MAGIC '*'

/* Request to register a user_event */
@@ -54,4 +75,7 @@ struct user_reg {
/* Request to delete a user_event */
#define DIAG_IOCSDEL _IOW(DIAG_IOC_MAGIC, 1, char *)

+/* Requests to unregister a user_event */
+#define DIAG_IOCSUNREG _IOW(DIAG_IOC_MAGIC, 2, struct user_unreg*)
+
#endif /* _UAPI_LINUX_USER_EVENTS_H */
diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index 86bda1660536..e4ee25d16f3b 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -102,6 +102,9 @@ struct user_event_enabler {
/* Bit 6 is for faulting status of enablement */
#define ENABLE_VAL_FAULTING_BIT 6

+/* Bit 7 is for freeing status of enablement */
+#define ENABLE_VAL_FREEING_BIT 7
+
/* Only duplicate the bit value */
#define ENABLE_VAL_DUP_MASK ENABLE_VAL_BIT_MASK

@@ -301,6 +304,12 @@ static void user_event_enabler_fault_fixup(struct work_struct *work)
/* Prevent state changes from racing */
mutex_lock(&event_mutex);

+ /* User asked for enabler to be removed during fault */
+ if (test_bit(ENABLE_VAL_FREEING_BIT, ENABLE_BITOPS(enabler))) {
+ user_event_enabler_destroy(enabler);
+ goto out;
+ }
+
/*
* If we managed to get the page, re-issue the write. We do not
* want to get into a possible infinite loop, which is why we only
@@ -315,7 +324,7 @@ static void user_event_enabler_fault_fixup(struct work_struct *work)
user_event_enabler_write(mm, enabler, true);
mmap_read_unlock(mm->mm);
}
-
+out:
mutex_unlock(&event_mutex);

/* In all cases we no longer need the mm or fault */
@@ -370,7 +379,8 @@ static int user_event_enabler_write(struct user_event_mm *mm,
if (refcount_read(&mm->tasks) == 0)
return -ENOENT;

- if (unlikely(test_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler))))
+ if (unlikely(test_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler)) ||
+ test_bit(ENABLE_VAL_FREEING_BIT, ENABLE_BITOPS(enabler))))
return -EBUSY;

ret = pin_user_pages_remote(mm->mm, uaddr, 1, FOLL_WRITE | FOLL_NOFAULT,
@@ -428,6 +438,10 @@ static bool user_event_enabler_dup(struct user_event_enabler *orig,
{
struct user_event_enabler *enabler;

+ /* Skip pending frees */
+ if (unlikely(test_bit(ENABLE_VAL_FREEING_BIT, ENABLE_BITOPS(orig))))
+ return true;
+
enabler = kzalloc(sizeof(*enabler), GFP_NOWAIT);

if (!enabler)
@@ -2086,6 +2100,75 @@ static long user_events_ioctl_del(struct user_event_file_info *info,
return ret;
}

+static long user_unreg_get(struct user_unreg __user *ureg,
+ struct user_unreg *kreg)
+{
+ u32 size;
+ long ret;
+
+ ret = get_user(size, &ureg->size);
+
+ if (ret)
+ return ret;
+
+ if (size > PAGE_SIZE)
+ return -E2BIG;
+
+ if (size < offsetofend(struct user_unreg, disable_addr))
+ return -EINVAL;
+
+ ret = copy_struct_from_user(kreg, sizeof(*kreg), ureg, size);
+
+ return ret;
+}
+
+/*
+ * Unregisters an enablement address/bit within a task/user mm.
+ */
+static long user_events_ioctl_unreg(unsigned long uarg)
+{
+ struct user_unreg __user *ureg = (struct user_unreg __user *)uarg;
+ struct user_event_mm *mm = current->user_event_mm;
+ struct user_event_enabler *enabler, *next;
+ struct user_unreg reg;
+ long ret;
+
+ ret = user_unreg_get(ureg, &reg);
+
+ if (ret)
+ return ret;
+
+ if (!mm)
+ return -ENOENT;
+
+ ret = -ENOENT;
+
+ /*
+ * Flags freeing and faulting are used to indicate if the enabler is in
+ * use at all. When faulting is set a page-fault is occurring asyncly.
+ * During async fault if freeing is set, the enabler will be destroyed.
+ * If no async fault is happening, we can destroy it now since we hold
+ * the event_mutex during these checks.
+ */
+ mutex_lock(&event_mutex);
+
+ list_for_each_entry_safe(enabler, next, &mm->enablers, link)
+ if (enabler->addr == reg.disable_addr &&
+ (enabler->values & ENABLE_VAL_BIT_MASK) == reg.disable_bit) {
+ set_bit(ENABLE_VAL_FREEING_BIT, ENABLE_BITOPS(enabler));
+
+ if (!test_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler)))
+ user_event_enabler_destroy(enabler);
+
+ /* Removed at least one */
+ ret = 0;
+ }
+
+ mutex_unlock(&event_mutex);
+
+ return ret;
+}
+
/*
* Handles the ioctl from user mode to register or alter operations.
*/
@@ -2108,6 +2191,12 @@ static long user_events_ioctl(struct file *file, unsigned int cmd,
ret = user_events_ioctl_del(info, uarg);
mutex_unlock(&group->reg_mutex);
break;
+
+ case DIAG_IOCSUNREG:
+ mutex_lock(&group->reg_mutex);
+ ret = user_events_ioctl_unreg(uarg);
+ mutex_unlock(&group->reg_mutex);
+ break;
}

return ret;
--
2.25.1

2023-02-21 21:12:07

by Beau Belgrave

[permalink] [raw]

Subject: [PATCH v8 08/11] tracing/user_events: Use write ABI in example

The ABI has changed to use a remote write approach. Update the example
to show the expected use of this new ABI. Also remove debugfs
path and use tracefs to ensure example works in more environments.

Signed-off-by: Beau Belgrave <[email protected]>
---
samples/user_events/example.c | 47 +++++++----------------------------
1 file changed, 9 insertions(+), 38 deletions(-)

diff --git a/samples/user_events/example.c b/samples/user_events/example.c
index d06dc24156ec..28165a096697 100644
--- a/samples/user_events/example.c
+++ b/samples/user_events/example.c
@@ -9,51 +9,28 @@
#include <errno.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
+#include <sys/uio.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
-#include <asm/bitsperlong.h>
-#include <endian.h>
#include <linux/user_events.h>

-#if __BITS_PER_LONG == 64
-#define endian_swap(x) htole64(x)
-#else
-#define endian_swap(x) htole32(x)
-#endif
+const char *data_file = "/sys/kernel/tracing/user_events_data";
+int enabled = 0;

-/* Assumes debugfs is mounted */
-const char *data_file = "/sys/kernel/debug/tracing/user_events_data";
-const char *status_file = "/sys/kernel/debug/tracing/user_events_status";
-
-static int event_status(long **status)
-{
- int fd = open(status_file, O_RDONLY);
-
- *status = mmap(NULL, sysconf(_SC_PAGESIZE), PROT_READ,
- MAP_SHARED, fd, 0);
-
- close(fd);
-
- if (*status == MAP_FAILED)
- return -1;
-
- return 0;
-}
-
-static int event_reg(int fd, const char *command, long *index, long *mask,
- int *write)
+static int event_reg(int fd, const char *command, int *write, int *enabled)
{
struct user_reg reg = {0};

reg.size = sizeof(reg);
+ reg.enable_bit = 31;
+ reg.enable_size = sizeof(*enabled);
+ reg.enable_addr = (__u64)enabled;
reg.name_args = (__u64)command;

if (ioctl(fd, DIAG_IOCSREG, &reg) == -1)
return -1;

- *index = reg.status_bit / __BITS_PER_LONG;
- *mask = endian_swap(1L << (reg.status_bit % __BITS_PER_LONG));
*write = reg.write_index;

return 0;
@@ -62,17 +39,12 @@ static int event_reg(int fd, const char *command, long *index, long *mask,
int main(int argc, char **argv)
{
int data_fd, write;
- long index, mask;
- long *status_page;
struct iovec io[2];
__u32 count = 0;

- if (event_status(&status_page) == -1)
- return errno;
-
data_fd = open(data_file, O_RDWR);

- if (event_reg(data_fd, "test u32 count", &index, &mask, &write) == -1)
+ if (event_reg(data_fd, "test u32 count", &write, &enabled) == -1)
return errno;

/* Setup iovec */
@@ -80,13 +52,12 @@ int main(int argc, char **argv)
io[0].iov_len = sizeof(write);
io[1].iov_base = &count;
io[1].iov_len = sizeof(count);
-
ask:
printf("Press enter to check status...\n");
getchar();

/* Check if anyone is listening */
- if (status_page[index] & mask) {
+ if (enabled) {
/* Yep, trace out our data */
writev(data_fd, (const struct iovec *)io, 2);

--
2.25.1

2023-02-21 21:12:09

by Beau Belgrave

[permalink] [raw]

Subject: [PATCH v8 07/11] tracing/user_events: Add ABI self-test

Add ABI specific self-test to ensure enablements work in various
scenarios such as fork, VM_CLONE, and basic event enable/disable.
Ensure ABI contracts/limits are also being upheld, such as bit limits
and data size limits.

Signed-off-by: Beau Belgrave <[email protected]>
---
tools/testing/selftests/user_events/Makefile | 2 +-
.../testing/selftests/user_events/abi_test.c | 226 ++++++++++++++++++
2 files changed, 227 insertions(+), 1 deletion(-)
create mode 100644 tools/testing/selftests/user_events/abi_test.c

diff --git a/tools/testing/selftests/user_events/Makefile b/tools/testing/selftests/user_events/Makefile
index c765d8635d9a..d5f64ef93197 100644
--- a/tools/testing/selftests/user_events/Makefile
+++ b/tools/testing/selftests/user_events/Makefile
@@ -2,7 +2,7 @@
CFLAGS += -Wl,-no-as-needed -Wall -I../../../../usr/include
LDLIBS += -lrt -lpthread -lm

-TEST_GEN_PROGS = ftrace_test dyn_test perf_test
+TEST_GEN_PROGS = ftrace_test dyn_test perf_test abi_test

TEST_FILES := settings

diff --git a/tools/testing/selftests/user_events/abi_test.c b/tools/testing/selftests/user_events/abi_test.c
new file mode 100644
index 000000000000..e0323d3777a7
--- /dev/null
+++ b/tools/testing/selftests/user_events/abi_test.c
@@ -0,0 +1,226 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * User Events ABI Test Program
+ *
+ * Copyright (c) 2022 Beau Belgrave <[email protected]>
+ */
+
+#define _GNU_SOURCE
+#include <sched.h>
+
+#include <errno.h>
+#include <linux/user_events.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <sys/ioctl.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <asm/unistd.h>
+
+#include "../kselftest_harness.h"
+
+const char *data_file = "/sys/kernel/tracing/user_events_data";
+const char *enable_file = "/sys/kernel/tracing/events/user_events/__abi_event/enable";
+
+static int change_event(bool enable)
+{
+ int fd = open(enable_file, O_RDWR);
+ int ret;
+
+ if (fd < 0)
+ return -1;
+
+ if (enable)
+ ret = write(fd, "1", 1);
+ else
+ ret = write(fd, "0", 1);
+
+ close(fd);
+
+ if (ret == 1)
+ ret = 0;
+ else
+ ret = -1;
+
+ return ret;
+}
+
+static int reg_enable(long *enable, int size, int bit)
+{
+ struct user_reg reg = {0};
+ int fd = open(data_file, O_RDWR);
+ int ret;
+
+ if (fd < 0)
+ return -1;
+
+ reg.size = sizeof(reg);
+ reg.name_args = (__u64)"__abi_event";
+ reg.enable_bit = bit;
+ reg.enable_addr = (__u64)enable;
+ reg.enable_size = size;
+
+ ret = ioctl(fd, DIAG_IOCSREG, &reg);
+
+ close(fd);
+
+ return ret;
+}
+
+static int reg_disable(long *enable, int bit)
+{
+ struct user_unreg reg = {0};
+ int fd = open(data_file, O_RDWR);
+ int ret;
+
+ if (fd < 0)
+ return -1;
+
+ reg.size = sizeof(reg);
+ reg.disable_bit = bit;
+ reg.disable_addr = (__u64)enable;
+
+ ret = ioctl(fd, DIAG_IOCSUNREG, &reg);
+
+ close(fd);
+
+ return ret;
+}
+
+FIXTURE(user) {
+ long check;
+};
+
+FIXTURE_SETUP(user) {
+ change_event(false);
+ self->check = 0;
+}
+
+FIXTURE_TEARDOWN(user) {
+}
+
+TEST_F(user, enablement) {
+ /* Changes should be reflected immediately */
+ ASSERT_EQ(0, self->check);
+ ASSERT_EQ(0, reg_enable(&self->check, sizeof(int), 0));
+ ASSERT_EQ(0, change_event(true));
+ ASSERT_EQ(1, self->check);
+ ASSERT_EQ(0, change_event(false));
+ ASSERT_EQ(0, self->check);
+
+ /* Should not change after disable */
+ ASSERT_EQ(0, change_event(true));
+ ASSERT_EQ(1, self->check);
+ ASSERT_EQ(0, reg_disable(&self->check, 0));
+ ASSERT_EQ(0, change_event(false));
+ ASSERT_EQ(1, self->check);
+ self->check = 0;
+}
+
+TEST_F(user, bit_sizes) {
+ /* Allow 0-31 bits for 32-bit */
+ ASSERT_EQ(0, reg_enable(&self->check, sizeof(int), 0));
+ ASSERT_EQ(0, reg_enable(&self->check, sizeof(int), 31));
+ ASSERT_NE(0, reg_enable(&self->check, sizeof(int), 32));
+ ASSERT_EQ(0, reg_disable(&self->check, 0));
+ ASSERT_EQ(0, reg_disable(&self->check, 31));
+
+#if BITS_PER_LONG == 8
+ /* Allow 0-64 bits for 64-bit */
+ ASSERT_EQ(0, reg_enable(&self->check, sizeof(long), 63));
+ ASSERT_NE(0, reg_enable(&self->check, sizeof(long), 64));
+ ASSERT_EQ(0, reg_disable(&self->check, 63));
+#endif
+
+ /* Disallowed sizes (everything beside 4 and 8) */
+ ASSERT_NE(0, reg_enable(&self->check, 1, 0));
+ ASSERT_NE(0, reg_enable(&self->check, 2, 0));
+ ASSERT_NE(0, reg_enable(&self->check, 3, 0));
+ ASSERT_NE(0, reg_enable(&self->check, 5, 0));
+ ASSERT_NE(0, reg_enable(&self->check, 6, 0));
+ ASSERT_NE(0, reg_enable(&self->check, 7, 0));
+ ASSERT_NE(0, reg_enable(&self->check, 9, 0));
+ ASSERT_NE(0, reg_enable(&self->check, 128, 0));
+}
+
+TEST_F(user, forks) {
+ int i;
+
+ /* Ensure COW pages get updated after fork */
+ ASSERT_EQ(0, reg_enable(&self->check, sizeof(int), 0));
+ ASSERT_EQ(0, self->check);
+
+ if (fork() == 0) {
+ /* Force COW */
+ self->check = 0;
+
+ /* Up to 1 sec for enablement */
+ for (i = 0; i < 10; ++i) {
+ usleep(100000);
+
+ if (self->check)
+ exit(0);
+ }
+
+ exit(1);
+ }
+
+ /* Allow generous time for COW, then enable */
+ usleep(100000);
+ ASSERT_EQ(0, change_event(true));
+
+ ASSERT_NE(-1, wait(&i));
+ ASSERT_EQ(0, WEXITSTATUS(i));
+
+ /* Ensure child doesn't disable parent */
+ if (fork() == 0)
+ exit(reg_disable(&self->check, 0));
+
+ ASSERT_NE(-1, wait(&i));
+ ASSERT_EQ(0, WEXITSTATUS(i));
+ ASSERT_EQ(1, self->check);
+ ASSERT_EQ(0, change_event(false));
+ ASSERT_EQ(0, self->check);
+}
+
+/* Waits up to 1 sec for enablement */
+static int clone_check(void *check)
+{
+ int i;
+
+ for (i = 0; i < 10; ++i) {
+ usleep(100000);
+
+ if (*(long *)check)
+ return 0;
+ }
+
+ return 1;
+}
+
+TEST_F(user, clones) {
+ int i, stack_size = 4096;
+ void *stack = mmap(NULL, stack_size, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK,
+ -1, 0);
+
+ ASSERT_NE(MAP_FAILED, stack);
+ ASSERT_EQ(0, reg_enable(&self->check, sizeof(int), 0));
+ ASSERT_EQ(0, self->check);
+
+ /* Shared VM should see enablements */
+ ASSERT_NE(-1, clone(&clone_check, stack + stack_size,
+ CLONE_VM | SIGCHLD, &self->check));
+
+ ASSERT_EQ(0, change_event(true));
+ ASSERT_NE(-1, wait(&i));
+ ASSERT_EQ(0, WEXITSTATUS(i));
+ munmap(stack, stack_size);
+ ASSERT_EQ(0, change_event(false));
+}
+
+int main(int argc, char **argv)
+{
+ return test_harness_run(argc, argv);
+}
--
2.25.1

2023-02-21 21:12:11

by Beau Belgrave

[permalink] [raw]

Subject: [PATCH v8 06/11] tracing/user_events: Update self-tests to write ABI

ABI has been changed to remote writes, update existing test cases to use
this new ABI to ensure existing functionality continues to work.

Signed-off-by: Beau Belgrave <[email protected]>
---
.../testing/selftests/user_events/dyn_test.c | 2 +-
.../selftests/user_events/ftrace_test.c | 162 ++++++++++--------
.../testing/selftests/user_events/perf_test.c | 39 ++---
3 files changed, 105 insertions(+), 98 deletions(-)

diff --git a/tools/testing/selftests/user_events/dyn_test.c b/tools/testing/selftests/user_events/dyn_test.c
index d6265d14cd51..8879a7b04c6a 100644
--- a/tools/testing/selftests/user_events/dyn_test.c
+++ b/tools/testing/selftests/user_events/dyn_test.c
@@ -16,7 +16,7 @@

#include "../kselftest_harness.h"

-const char *dyn_file = "/sys/kernel/debug/tracing/dynamic_events";
+const char *dyn_file = "/sys/kernel/tracing/dynamic_events";
const char *clear = "!u:__test_event";

static int Append(const char *value)
diff --git a/tools/testing/selftests/user_events/ftrace_test.c b/tools/testing/selftests/user_events/ftrace_test.c
index 404a2713dcae..aceafacfb126 100644
--- a/tools/testing/selftests/user_events/ftrace_test.c
+++ b/tools/testing/selftests/user_events/ftrace_test.c
@@ -12,20 +12,16 @@
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
+#include <sys/uio.h>
#include <unistd.h>

#include "../kselftest_harness.h"

-const char *data_file = "/sys/kernel/debug/tracing/user_events_data";
-const char *status_file = "/sys/kernel/debug/tracing/user_events_status";
-const char *enable_file = "/sys/kernel/debug/tracing/events/user_events/__test_event/enable";
-const char *trace_file = "/sys/kernel/debug/tracing/trace";
-const char *fmt_file = "/sys/kernel/debug/tracing/events/user_events/__test_event/format";
-
-static inline int status_check(char *status_page, int status_bit)
-{
- return status_page[status_bit >> 3] & (1 << (status_bit & 7));
-}
+const char *data_file = "/sys/kernel/tracing/user_events_data";
+const char *status_file = "/sys/kernel/tracing/user_events_status";
+const char *enable_file = "/sys/kernel/tracing/events/user_events/__test_event/enable";
+const char *trace_file = "/sys/kernel/tracing/trace";
+const char *fmt_file = "/sys/kernel/tracing/events/user_events/__test_event/format";

static int trace_bytes(void)
{
@@ -106,13 +102,23 @@ static int get_print_fmt(char *buffer, int len)
return -1;
}

-static int clear(void)
+static int clear(int *check)
{
+ struct user_unreg unreg = {0};
+
+ unreg.size = sizeof(unreg);
+ unreg.disable_bit = 31;
+ unreg.disable_addr = (__u64)check;
+
int fd = open(data_file, O_RDWR);

if (fd == -1)
return -1;

+ if (ioctl(fd, DIAG_IOCSUNREG, &unreg) == -1)
+ if (errno != ENOENT)
+ return -1;
+
if (ioctl(fd, DIAG_IOCSDEL, "__test_event") == -1)
if (errno != ENOENT)
return -1;
@@ -122,7 +128,7 @@ static int clear(void)
return 0;
}

-static int check_print_fmt(const char *event, const char *expected)
+static int check_print_fmt(const char *event, const char *expected, int *check)
{
struct user_reg reg = {0};
char print_fmt[256];
@@ -130,7 +136,7 @@ static int check_print_fmt(const char *event, const char *expected)
int fd;

/* Ensure cleared */
- ret = clear();
+ ret = clear(check);

if (ret != 0)
return ret;
@@ -142,14 +148,19 @@ static int check_print_fmt(const char *event, const char *expected)

reg.size = sizeof(reg);
reg.name_args = (__u64)event;
+ reg.enable_bit = 31;
+ reg.enable_addr = (__u64)check;
+ reg.enable_size = sizeof(*check);

/* Register should work */
ret = ioctl(fd, DIAG_IOCSREG, &reg);

close(fd);

- if (ret != 0)
+ if (ret != 0) {
+ printf("Reg failed in fmt\n");
return ret;
+ }

/* Ensure correct print_fmt */
ret = get_print_fmt(print_fmt, sizeof(print_fmt));
@@ -164,6 +175,7 @@ FIXTURE(user) {
int status_fd;
int data_fd;
int enable_fd;
+ int check;
};

FIXTURE_SETUP(user) {
@@ -185,59 +197,56 @@ FIXTURE_TEARDOWN(user) {
close(self->enable_fd);
}

- ASSERT_EQ(0, clear());
+ if (clear(&self->check) != 0)
+ printf("WARNING: Clear didn't work!\n");
}

TEST_F(user, register_events) {
struct user_reg reg = {0};
- int page_size = sysconf(_SC_PAGESIZE);
- char *status_page;
+ struct user_unreg unreg = {0};

reg.size = sizeof(reg);
reg.name_args = (__u64)"__test_event u32 field1; u32 field2";
+ reg.enable_bit = 31;
+ reg.enable_addr = (__u64)&self->check;
+ reg.enable_size = sizeof(self->check);

- status_page = mmap(NULL, page_size, PROT_READ, MAP_SHARED,
- self->status_fd, 0);
+ unreg.size = sizeof(unreg);
+ unreg.disable_bit = 31;
+ unreg.disable_addr = (__u64)&self->check;

/* Register should work */
ASSERT_EQ(0, ioctl(self->data_fd, DIAG_IOCSREG, &reg));
ASSERT_EQ(0, reg.write_index);
- ASSERT_NE(0, reg.status_bit);

/* Multiple registers should result in same index */
ASSERT_EQ(0, ioctl(self->data_fd, DIAG_IOCSREG, &reg));
ASSERT_EQ(0, reg.write_index);
- ASSERT_NE(0, reg.status_bit);

/* Ensure disabled */
self->enable_fd = open(enable_file, O_RDWR);
ASSERT_NE(-1, self->enable_fd);
ASSERT_NE(-1, write(self->enable_fd, "0", sizeof("0")))

- /* MMAP should work and be zero'd */
- ASSERT_NE(MAP_FAILED, status_page);
- ASSERT_NE(NULL, status_page);
- ASSERT_EQ(0, status_check(status_page, reg.status_bit));
-
/* Enable event and ensure bits updated in status */
ASSERT_NE(-1, write(self->enable_fd, "1", sizeof("1")))
- ASSERT_NE(0, status_check(status_page, reg.status_bit));
+ ASSERT_EQ(1 << reg.enable_bit, self->check);

/* Disable event and ensure bits updated in status */
ASSERT_NE(-1, write(self->enable_fd, "0", sizeof("0")))
- ASSERT_EQ(0, status_check(status_page, reg.status_bit));
+ ASSERT_EQ(0, self->check);

/* File still open should return -EBUSY for delete */
ASSERT_EQ(-1, ioctl(self->data_fd, DIAG_IOCSDEL, "__test_event"));
ASSERT_EQ(EBUSY, errno);

- /* Delete should work only after close */
+ /* Unregister */
+ ASSERT_EQ(0, ioctl(self->data_fd, DIAG_IOCSUNREG, &unreg));
+
+ /* Delete should work only after close and unregister */
close(self->data_fd);
self->data_fd = open(data_file, O_RDWR);
ASSERT_EQ(0, ioctl(self->data_fd, DIAG_IOCSDEL, "__test_event"));
-
- /* Unmap should work */
- ASSERT_EQ(0, munmap(status_page, page_size));
}

TEST_F(user, write_events) {
@@ -245,11 +254,12 @@ TEST_F(user, write_events) {
struct iovec io[3];
__u32 field1, field2;
int before = 0, after = 0;
- int page_size = sysconf(_SC_PAGESIZE);
- char *status_page;

reg.size = sizeof(reg);
reg.name_args = (__u64)"__test_event u32 field1; u32 field2";
+ reg.enable_bit = 31;
+ reg.enable_addr = (__u64)&self->check;
+ reg.enable_size = sizeof(self->check);

field1 = 1;
field2 = 2;
@@ -261,18 +271,10 @@ TEST_F(user, write_events) {
io[2].iov_base = &field2;
io[2].iov_len = sizeof(field2);

- status_page = mmap(NULL, page_size, PROT_READ, MAP_SHARED,
- self->status_fd, 0);
-
/* Register should work */
ASSERT_EQ(0, ioctl(self->data_fd, DIAG_IOCSREG, &reg));
ASSERT_EQ(0, reg.write_index);
- ASSERT_NE(0, reg.status_bit);
-
- /* MMAP should work and be zero'd */
- ASSERT_NE(MAP_FAILED, status_page);
- ASSERT_NE(NULL, status_page);
- ASSERT_EQ(0, status_check(status_page, reg.status_bit));
+ ASSERT_EQ(0, self->check);

/* Write should fail on invalid slot with ENOENT */
io[0].iov_base = &field2;
@@ -287,7 +289,7 @@ TEST_F(user, write_events) {
ASSERT_NE(-1, write(self->enable_fd, "1", sizeof("1")))

/* Event should now be enabled */
- ASSERT_NE(0, status_check(status_page, reg.status_bit));
+ ASSERT_NE(1 << reg.enable_bit, self->check);

/* Write should make it out to ftrace buffers */
before = trace_bytes();
@@ -304,6 +306,9 @@ TEST_F(user, write_fault) {

reg.size = sizeof(reg);
reg.name_args = (__u64)"__test_event u64 anon";
+ reg.enable_bit = 31;
+ reg.enable_addr = (__u64)&self->check;
+ reg.enable_size = sizeof(self->check);

anon = mmap(NULL, l, PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
ASSERT_NE(MAP_FAILED, anon);
@@ -316,7 +321,6 @@ TEST_F(user, write_fault) {
/* Register should work */
ASSERT_EQ(0, ioctl(self->data_fd, DIAG_IOCSREG, &reg));
ASSERT_EQ(0, reg.write_index);
- ASSERT_NE(0, reg.status_bit);

/* Write should work normally */
ASSERT_NE(-1, writev(self->data_fd, (const struct iovec *)io, 2));
@@ -333,24 +337,17 @@ TEST_F(user, write_validator) {
int loc, bytes;
char data[8];
int before = 0, after = 0;
- int page_size = sysconf(_SC_PAGESIZE);
- char *status_page;
-
- status_page = mmap(NULL, page_size, PROT_READ, MAP_SHARED,
- self->status_fd, 0);

reg.size = sizeof(reg);
reg.name_args = (__u64)"__test_event __rel_loc char[] data";
+ reg.enable_bit = 31;
+ reg.enable_addr = (__u64)&self->check;
+ reg.enable_size = sizeof(self->check);

/* Register should work */
ASSERT_EQ(0, ioctl(self->data_fd, DIAG_IOCSREG, &reg));
ASSERT_EQ(0, reg.write_index);
- ASSERT_NE(0, reg.status_bit);
-
- /* MMAP should work and be zero'd */
- ASSERT_NE(MAP_FAILED, status_page);
- ASSERT_NE(NULL, status_page);
- ASSERT_EQ(0, status_check(status_page, reg.status_bit));
+ ASSERT_EQ(0, self->check);

io[0].iov_base = &reg.write_index;
io[0].iov_len = sizeof(reg.write_index);
@@ -369,7 +366,7 @@ TEST_F(user, write_validator) {
ASSERT_NE(-1, write(self->enable_fd, "1", sizeof("1")))

/* Event should now be enabled */
- ASSERT_NE(0, status_check(status_page, reg.status_bit));
+ ASSERT_EQ(1 << reg.enable_bit, self->check);

/* Full in-bounds write should work */
before = trace_bytes();
@@ -409,71 +406,88 @@ TEST_F(user, print_fmt) {
int ret;

ret = check_print_fmt("__test_event __rel_loc char[] data",
- "print fmt: \"data=%s\", __get_rel_str(data)");
+ "print fmt: \"data=%s\", __get_rel_str(data)",
+ &self->check);
ASSERT_EQ(0, ret);

ret = check_print_fmt("__test_event __data_loc char[] data",
- "print fmt: \"data=%s\", __get_str(data)");
+ "print fmt: \"data=%s\", __get_str(data)",
+ &self->check);
ASSERT_EQ(0, ret);

ret = check_print_fmt("__test_event s64 data",
- "print fmt: \"data=%lld\", REC->data");
+ "print fmt: \"data=%lld\", REC->data",
+ &self->check);
ASSERT_EQ(0, ret);

ret = check_print_fmt("__test_event u64 data",
- "print fmt: \"data=%llu\", REC->data");
+ "print fmt: \"data=%llu\", REC->data",
+ &self->check);
ASSERT_EQ(0, ret);

ret = check_print_fmt("__test_event s32 data",
- "print fmt: \"data=%d\", REC->data");
+ "print fmt: \"data=%d\", REC->data",
+ &self->check);
ASSERT_EQ(0, ret);

ret = check_print_fmt("__test_event u32 data",
- "print fmt: \"data=%u\", REC->data");
+ "print fmt: \"data=%u\", REC->data",
+ &self->check);
ASSERT_EQ(0, ret);

ret = check_print_fmt("__test_event int data",
- "print fmt: \"data=%d\", REC->data");
+ "print fmt: \"data=%d\", REC->data",
+ &self->check);
ASSERT_EQ(0, ret);

ret = check_print_fmt("__test_event unsigned int data",
- "print fmt: \"data=%u\", REC->data");
+ "print fmt: \"data=%u\", REC->data",
+ &self->check);
ASSERT_EQ(0, ret);

ret = check_print_fmt("__test_event s16 data",
- "print fmt: \"data=%d\", REC->data");
+ "print fmt: \"data=%d\", REC->data",
+ &self->check);
ASSERT_EQ(0, ret);

ret = check_print_fmt("__test_event u16 data",
- "print fmt: \"data=%u\", REC->data");
+ "print fmt: \"data=%u\", REC->data",
+ &self->check);
ASSERT_EQ(0, ret);

ret = check_print_fmt("__test_event short data",
- "print fmt: \"data=%d\", REC->data");
+ "print fmt: \"data=%d\", REC->data",
+ &self->check);
ASSERT_EQ(0, ret);

ret = check_print_fmt("__test_event unsigned short data",
- "print fmt: \"data=%u\", REC->data");
+ "print fmt: \"data=%u\", REC->data",
+ &self->check);
ASSERT_EQ(0, ret);

ret = check_print_fmt("__test_event s8 data",
- "print fmt: \"data=%d\", REC->data");
+ "print fmt: \"data=%d\", REC->data",
+ &self->check);
ASSERT_EQ(0, ret);

ret = check_print_fmt("__test_event u8 data",
- "print fmt: \"data=%u\", REC->data");
+ "print fmt: \"data=%u\", REC->data",
+ &self->check);
ASSERT_EQ(0, ret);

ret = check_print_fmt("__test_event char data",
- "print fmt: \"data=%d\", REC->data");
+ "print fmt: \"data=%d\", REC->data",
+ &self->check);
ASSERT_EQ(0, ret);

ret = check_print_fmt("__test_event unsigned char data",
- "print fmt: \"data=%u\", REC->data");
+ "print fmt: \"data=%u\", REC->data",
+ &self->check);
ASSERT_EQ(0, ret);

ret = check_print_fmt("__test_event char[4] data",
- "print fmt: \"data=%s\", REC->data");
+ "print fmt: \"data=%s\", REC->data",
+ &self->check);
ASSERT_EQ(0, ret);
}

diff --git a/tools/testing/selftests/user_events/perf_test.c b/tools/testing/selftests/user_events/perf_test.c
index 8b4c7879d5a7..a070258d4449 100644
--- a/tools/testing/selftests/user_events/perf_test.c
+++ b/tools/testing/selftests/user_events/perf_test.c
@@ -18,10 +18,9 @@

#include "../kselftest_harness.h"

-const char *data_file = "/sys/kernel/debug/tracing/user_events_data";
-const char *status_file = "/sys/kernel/debug/tracing/user_events_status";
-const char *id_file = "/sys/kernel/debug/tracing/events/user_events/__test_event/id";
-const char *fmt_file = "/sys/kernel/debug/tracing/events/user_events/__test_event/format";
+const char *data_file = "/sys/kernel/tracing/user_events_data";
+const char *id_file = "/sys/kernel/tracing/events/user_events/__test_event/id";
+const char *fmt_file = "/sys/kernel/tracing/events/user_events/__test_event/format";

struct event {
__u32 index;
@@ -35,11 +34,6 @@ static long perf_event_open(struct perf_event_attr *pe, pid_t pid,
return syscall(__NR_perf_event_open, pe, pid, cpu, group_fd, flags);
}

-static inline int status_check(char *status_page, int status_bit)
-{
- return status_page[status_bit >> 3] & (1 << (status_bit & 7));
-}
-
static int get_id(void)
{
FILE *fp = fopen(id_file, "r");
@@ -88,45 +82,38 @@ static int get_offset(void)
}

FIXTURE(user) {
- int status_fd;
int data_fd;
+ int check;
};

FIXTURE_SETUP(user) {
- self->status_fd = open(status_file, O_RDONLY);
- ASSERT_NE(-1, self->status_fd);
-
self->data_fd = open(data_file, O_RDWR);
ASSERT_NE(-1, self->data_fd);
}

FIXTURE_TEARDOWN(user) {
- close(self->status_fd);
close(self->data_fd);
}

TEST_F(user, perf_write) {
struct perf_event_attr pe = {0};
struct user_reg reg = {0};
- int page_size = sysconf(_SC_PAGESIZE);
- char *status_page;
struct event event;
struct perf_event_mmap_page *perf_page;
+ int page_size = sysconf(_SC_PAGESIZE);
int id, fd, offset;
__u32 *val;

reg.size = sizeof(reg);
reg.name_args = (__u64)"__test_event u32 field1; u32 field2";
-
- status_page = mmap(NULL, page_size, PROT_READ, MAP_SHARED,
- self->status_fd, 0);
- ASSERT_NE(MAP_FAILED, status_page);
+ reg.enable_bit = 31;
+ reg.enable_addr = (__u64)&self->check;
+ reg.enable_size = sizeof(self->check);

/* Register should work */
ASSERT_EQ(0, ioctl(self->data_fd, DIAG_IOCSREG, &reg));
ASSERT_EQ(0, reg.write_index);
- ASSERT_NE(0, reg.status_bit);
- ASSERT_EQ(0, status_check(status_page, reg.status_bit));
+ ASSERT_EQ(0, self->check);

/* Id should be there */
id = get_id();
@@ -149,7 +136,7 @@ TEST_F(user, perf_write) {
ASSERT_NE(MAP_FAILED, perf_page);

/* Status should be updated */
- ASSERT_NE(0, status_check(status_page, reg.status_bit));
+ ASSERT_EQ(1 << reg.enable_bit, self->check);

event.index = reg.write_index;
event.field1 = 0xc001;
@@ -165,6 +152,12 @@ TEST_F(user, perf_write) {
/* Ensure correct */
ASSERT_EQ(event.field1, *val++);
ASSERT_EQ(event.field2, *val++);
+
+ munmap(perf_page, page_size * 2);
+ close(fd);
+
+ /* Status should be updated */
+ ASSERT_EQ(0, self->check);
}

int main(int argc, char **argv)
--
2.25.1

2023-02-21 21:12:14

by Beau Belgrave

[permalink] [raw]

Subject: [PATCH v8 10/11] tracing/user_events: Charge event allocs to cgroups

Operators need a way to limit how much memory cgroups use. User events need
to be included into that accounting. Fix this by using GFP_KERNEL_ACCOUNT
for allocations generated by user programs for user_event tracing.

Signed-off-by: Beau Belgrave <[email protected]>
---
kernel/trace/trace_events_user.c | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index e4ee25d16f3b..222f2eb59c7c 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -442,7 +442,7 @@ static bool user_event_enabler_dup(struct user_event_enabler *orig,
if (unlikely(test_bit(ENABLE_VAL_FREEING_BIT, ENABLE_BITOPS(orig))))
return true;

- enabler = kzalloc(sizeof(*enabler), GFP_NOWAIT);
+ enabler = kzalloc(sizeof(*enabler), GFP_NOWAIT | __GFP_ACCOUNT);

if (!enabler)
return false;
@@ -502,7 +502,7 @@ static struct user_event_mm *user_event_mm_create(struct task_struct *t)
struct user_event_mm *user_mm;
unsigned long flags;

- user_mm = kzalloc(sizeof(*user_mm), GFP_KERNEL);
+ user_mm = kzalloc(sizeof(*user_mm), GFP_KERNEL_ACCOUNT);

if (!user_mm)
return NULL;
@@ -662,7 +662,7 @@ static struct user_event_enabler
if (!user_mm)
return NULL;

- enabler = kzalloc(sizeof(*enabler), GFP_KERNEL);
+ enabler = kzalloc(sizeof(*enabler), GFP_KERNEL_ACCOUNT);

if (!enabler)
goto out;
@@ -870,7 +870,7 @@ static int user_event_add_field(struct user_event *user, const char *type,
struct ftrace_event_field *field;
int validator_flags = 0;

- field = kmalloc(sizeof(*field), GFP_KERNEL);
+ field = kmalloc(sizeof(*field), GFP_KERNEL_ACCOUNT);

if (!field)
return -ENOMEM;
@@ -889,7 +889,7 @@ static int user_event_add_field(struct user_event *user, const char *type,
if (strstr(type, "char") != NULL)
validator_flags |= VALIDATOR_ENSURE_NULL;

- validator = kmalloc(sizeof(*validator), GFP_KERNEL);
+ validator = kmalloc(sizeof(*validator), GFP_KERNEL_ACCOUNT);

if (!validator) {
kfree(field);
@@ -1175,7 +1175,7 @@ static int user_event_create_print_fmt(struct user_event *user)

len = user_event_set_print_fmt(user, NULL, 0);

- print_fmt = kmalloc(len, GFP_KERNEL);
+ print_fmt = kmalloc(len, GFP_KERNEL_ACCOUNT);

if (!print_fmt)
return -ENOMEM;
@@ -1508,7 +1508,7 @@ static int user_event_create(const char *raw_command)
raw_command += USER_EVENTS_PREFIX_LEN;
raw_command = skip_spaces(raw_command);

- name = kstrdup(raw_command, GFP_KERNEL);
+ name = kstrdup(raw_command, GFP_KERNEL_ACCOUNT);

if (!name)
return -ENOMEM;
@@ -1704,7 +1704,7 @@ static int user_event_parse(struct user_event_group *group, char *name,
return 0;
}

- user = kzalloc(sizeof(*user), GFP_KERNEL);
+ user = kzalloc(sizeof(*user), GFP_KERNEL_ACCOUNT);

if (!user)
return -ENOMEM;
@@ -1874,7 +1874,7 @@ static int user_events_open(struct inode *node, struct file *file)
if (!group)
return -ENOENT;

- info = kzalloc(sizeof(*info), GFP_KERNEL);
+ info = kzalloc(sizeof(*info), GFP_KERNEL_ACCOUNT);

if (!info)
return -ENOMEM;
@@ -1927,7 +1927,7 @@ static int user_events_ref_add(struct user_event_file_info *info,

size = struct_size(refs, events, count + 1);

- new_refs = kzalloc(size, GFP_KERNEL);
+ new_refs = kzalloc(size, GFP_KERNEL_ACCOUNT);

if (!new_refs)
return -ENOMEM;
--
2.25.1

2023-02-21 21:12:18

by Beau Belgrave

[permalink] [raw]

Subject: [PATCH v8 03/11] tracing/user_events: Use remote writes for event enablement

As part of the discussions for user_events aligned with user space
tracers, it was determined that user programs should register a aligned
value to set or clear a bit when an event becomes enabled. Currently a
shared page is being used that requires mmap(). Remove the shared page
implementation and move to a user registered address implementation.

In this new model during the event registration from user programs 3 new
values are specified. The first is the address to update when the event
is either enabled or disabled. The second is the bit to set/clear to
reflect the event being enabled. The third is the size of the value at
the specified address.

This allows for a local 32/64-bit value in user programs to support
both kernel and user tracers. As an example, setting bit 31 for kernel
tracers when the event becomes enabled allows for user tracers to use
the other bits for ref counts or other flags. The kernel side updates
the bit atomically, user programs need to also update these values
atomically.

User provided addresses must be aligned on a natural boundary, this
allows for single page checking and prevents odd behaviors such as a
enable value straddling 2 pages instead of a single page. Currently
page faults are only logged, future patches will handle these.

Suggested-by: Mathieu Desnoyers <[email protected]>
Signed-off-by: Beau Belgrave <[email protected]>
---
include/linux/user_events.h | 53 ++-
include/uapi/linux/user_events.h | 15 +-
kernel/trace/Kconfig | 5 +-
kernel/trace/trace_events_user.c | 586 ++++++++++++++++++++++++-------
4 files changed, 517 insertions(+), 142 deletions(-)

diff --git a/include/linux/user_events.h b/include/linux/user_events.h
index 3d747c45d2fa..0120b3dd5b03 100644
--- a/include/linux/user_events.h
+++ b/include/linux/user_events.h
@@ -9,13 +9,63 @@
#ifndef _LINUX_USER_EVENTS_H
#define _LINUX_USER_EVENTS_H

+#include <linux/list.h>
+#include <linux/refcount.h>
+#include <linux/mm_types.h>
+#include <linux/workqueue.h>
#include <uapi/linux/user_events.h>

#ifdef CONFIG_USER_EVENTS
struct user_event_mm {
+ struct list_head link;
+ struct list_head enablers;
+ struct mm_struct *mm;
+ struct user_event_mm *next;
+ refcount_t refcnt;
+ refcount_t tasks;
+ struct rcu_work put_rwork;
};
-#endif

+extern void user_event_mm_dup(struct task_struct *t,
+ struct user_event_mm *old_mm);
+
+extern void user_event_mm_remove(struct task_struct *t);
+
+static inline void user_events_fork(struct task_struct *t,
+ unsigned long clone_flags)
+{
+ struct user_event_mm *old_mm;
+
+ if (!t || !current->user_event_mm)
+ return;
+
+ old_mm = current->user_event_mm;
+
+ if (clone_flags & CLONE_VM) {
+ t->user_event_mm = old_mm;
+ refcount_inc(&old_mm->tasks);
+ return;
+ }
+
+ user_event_mm_dup(t, old_mm);
+}
+
+static inline void user_events_execve(struct task_struct *t)
+{
+ if (!t || !t->user_event_mm)
+ return;
+
+ user_event_mm_remove(t);
+}
+
+static inline void user_events_exit(struct task_struct *t)
+{
+ if (!t || !t->user_event_mm)
+ return;
+
+ user_event_mm_remove(t);
+}
+#else
static inline void user_events_fork(struct task_struct *t,
unsigned long clone_flags)
{
@@ -28,5 +78,6 @@ static inline void user_events_execve(struct task_struct *t)
static inline void user_events_exit(struct task_struct *t)
{
}
+#endif /* CONFIG_USER_EVENTS */

#endif /* _LINUX_USER_EVENTS_H */
diff --git a/include/uapi/linux/user_events.h b/include/uapi/linux/user_events.h
index 03f92366068d..22521bc622db 100644
--- a/include/uapi/linux/user_events.h
+++ b/include/uapi/linux/user_events.h
@@ -27,12 +27,21 @@ struct user_reg {
/* Input: Size of the user_reg structure being used */
__u32 size;

+ /* Input: Bit in enable address to use */
+ __u8 enable_bit;
+
+ /* Input: Enable size in bytes at address */
+ __u8 enable_size;
+
+ /* Input: Flags for future use, set to 0 */
+ __u16 flags;
+
+ /* Input: Address to update when enabled */
+ __u64 enable_addr;
+
/* Input: Pointer to string with event name, description and flags */
__u64 name_args;

- /* Output: Bitwise index of the event within the status page */
- __u32 status_bit;
-
/* Output: Index of the event to use when writing data */
__u32 write_index;
} __attribute__((__packed__));
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index d7043043f59c..b61a1bfbfc22 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -791,9 +791,10 @@ config USER_EVENTS
can be used like an existing kernel trace event. User trace
events are generated by writing to a tracefs file. User
processes can determine if their tracing events should be
- generated by memory mapping a tracefs file and checking for
- an associated byte being non-zero.
+ generated by registering a value and bit with the kernel
+ that reflects when it is enabled or not.

+ See Documentation/trace/user_events.rst.
If in doubt, say N.

config HIST_TRIGGERS
diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index 070551480747..553a82ee7aeb 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -19,6 +19,7 @@
#include <linux/tracefs.h>
#include <linux/types.h>
#include <linux/uaccess.h>
+#include <linux/highmem.h>
#include <linux/user_events.h>
#include "trace.h"
#include "trace_dynevent.h"
@@ -29,34 +30,11 @@
#define FIELD_DEPTH_NAME 1
#define FIELD_DEPTH_SIZE 2

-/*
- * Limits how many trace_event calls user processes can create:
- * Must be a power of two of PAGE_SIZE.
- */
-#define MAX_PAGE_ORDER 0
-#define MAX_PAGES (1 << MAX_PAGE_ORDER)
-#define MAX_BYTES (MAX_PAGES * PAGE_SIZE)
-#define MAX_EVENTS (MAX_BYTES * 8)
-
/* Limit how long of an event name plus args within the subsystem. */
#define MAX_EVENT_DESC 512
#define EVENT_NAME(user_event) ((user_event)->tracepoint.name)
#define MAX_FIELD_ARRAY_SIZE 1024

-/*
- * The MAP_STATUS_* macros are used for taking a index and determining the
- * appropriate byte and the bit in the byte to set/reset for an event.
- *
- * The lower 3 bits of the index decide which bit to set.
- * The remaining upper bits of the index decide which byte to use for the bit.
- *
- * This is used when an event has a probe attached/removed to reflect live
- * status of the event wanting tracing or not to user-programs via shared
- * memory maps.
- */
-#define MAP_STATUS_BYTE(index) ((index) >> 3)
-#define MAP_STATUS_MASK(index) BIT((index) & 7)
-
/*
* Internal bits (kernel side only) to keep track of connected probes:
* These are used when status is requested in text form about an event. These
@@ -70,20 +48,14 @@
#define EVENT_STATUS_OTHER BIT(7)

/*
- * Stores the pages, tables, and locks for a group of events.
- * Each logical grouping of events has its own group, with a
- * matching page for status checks within user programs. This
- * allows for isolation of events to user programs by various
- * means.
+ * Stores the system name, tables, and locks for a group of events. This
+ * allows isolation for events by various means.
*/
struct user_event_group {
- struct page *pages;
- char *register_page_data;
char *system_name;
struct hlist_node node;
struct mutex reg_mutex;
DECLARE_HASHTABLE(register_table, 8);
- DECLARE_BITMAP(page_bitmap, MAX_EVENTS);
};

/* Group for init_user_ns mapping, top-most group */
@@ -106,12 +78,34 @@ struct user_event {
struct list_head fields;
struct list_head validators;
refcount_t refcnt;
- int index;
- int flags;
int min_size;
char status;
};

+/*
+ * Stores per-mm/event properties that enable an address to be
+ * updated properly for each task. As tasks are forked, we use
+ * these to track enablement sites that are tied to an event.
+ */
+struct user_event_enabler {
+ struct list_head link;
+ struct user_event *event;
+ unsigned long addr;
+
+ /* Track enable bit, flags, etc. Aligned for bitops. */
+ unsigned int values;
+};
+
+/* Bits 0-5 are for the bit to update upon enable/disable (0-63 allowed) */
+#define ENABLE_VAL_BIT_MASK 0x3F
+
+/* Only duplicate the bit value */
+#define ENABLE_VAL_DUP_MASK ENABLE_VAL_BIT_MASK
+
+/* Global list of memory descriptors using user_events */
+static LIST_HEAD(user_event_mms);
+static DEFINE_SPINLOCK(user_event_mms_lock);
+
/*
* Stores per-file events references, as users register events
* within a file this structure is modified and freed via RCU.
@@ -145,33 +139,17 @@ static int user_event_parse(struct user_event_group *group, char *name,
char *args, char *flags,
struct user_event **newuser);

+static struct user_event_mm *user_event_mm_get(struct user_event_mm *mm);
+static struct user_event_mm *user_event_mm_get_all(struct user_event *user);
+static void user_event_mm_put(struct user_event_mm *mm);
+
static u32 user_event_key(char *name)
{
return jhash(name, strlen(name), 0);
}

-static void set_page_reservations(char *pages, bool set)
-{
- int page;
-
- for (page = 0; page < MAX_PAGES; ++page) {
- void *addr = pages + (PAGE_SIZE * page);
-
- if (set)
- SetPageReserved(virt_to_page(addr));
- else
- ClearPageReserved(virt_to_page(addr));
- }
-}
-
static void user_event_group_destroy(struct user_event_group *group)
{
- if (group->register_page_data)
- set_page_reservations(group->register_page_data, false);
-
- if (group->pages)
- __free_pages(group->pages, MAX_PAGE_ORDER);
-
kfree(group->system_name);
kfree(group);
}
@@ -242,19 +220,6 @@ static struct user_event_group
if (!group->system_name)
goto error;

- group->pages = alloc_pages(GFP_KERNEL | __GFP_ZERO, MAX_PAGE_ORDER);
-
- if (!group->pages)
- goto error;
-
- group->register_page_data = page_address(group->pages);
-
- set_page_reservations(group->register_page_data, true);
-
- /* Zero all bits beside 0 (which is reserved for failures) */
- bitmap_zero(group->page_bitmap, MAX_EVENTS);
- set_bit(0, group->page_bitmap);
-
mutex_init(&group->reg_mutex);
hash_init(group->register_table);

@@ -266,20 +231,367 @@ static struct user_event_group
return NULL;
};

-static __always_inline
-void user_event_register_set(struct user_event *user)
+static void user_event_enabler_destroy(struct user_event_enabler *enabler)
+{
+ list_del_rcu(&enabler->link);
+
+ /* No longer tracking the event via the enabler */
+ refcount_dec(&enabler->event->refcnt);
+
+ kfree(enabler);
+}
+
+static int user_event_mm_fault_in(struct user_event_mm *mm, unsigned long uaddr)
+{
+ bool unlocked;
+ int ret;
+
+ mmap_read_lock(mm->mm);
+
+ /* Ensure MM has tasks, cannot use after exit_mm() */
+ if (refcount_read(&mm->tasks) == 0) {
+ ret = -ENOENT;
+ goto out;
+ }
+
+ ret = fixup_user_fault(mm->mm, uaddr, FAULT_FLAG_WRITE | FAULT_FLAG_REMOTE,
+ &unlocked);
+out:
+ mmap_read_unlock(mm->mm);
+
+ return ret;
+}
+
+static int user_event_enabler_write(struct user_event_mm *mm,
+ struct user_event_enabler *enabler)
+{
+ unsigned long uaddr = enabler->addr;
+ unsigned long *ptr;
+ struct page *page;
+ void *kaddr;
+ int ret;
+
+ lockdep_assert_held(&event_mutex);
+ mmap_assert_locked(mm->mm);
+
+ /* Ensure MM has tasks, cannot use after exit_mm() */
+ if (refcount_read(&mm->tasks) == 0)
+ return -ENOENT;
+
+ ret = pin_user_pages_remote(mm->mm, uaddr, 1, FOLL_WRITE | FOLL_NOFAULT,
+ &page, NULL, NULL);
+
+ if (ret <= 0) {
+ pr_warn("user_events: Enable write failed\n");
+ return -EFAULT;
+ }
+
+ kaddr = kmap_local_page(page);
+ ptr = kaddr + (uaddr & ~PAGE_MASK);
+
+ /* Update bit atomically, user tracers must be atomic as well */
+ if (enabler->event && enabler->event->status)
+ set_bit(enabler->values & ENABLE_VAL_BIT_MASK, ptr);
+ else
+ clear_bit(enabler->values & ENABLE_VAL_BIT_MASK, ptr);
+
+ kunmap_local(kaddr);
+ unpin_user_pages_dirty_lock(&page, 1, true);
+
+ return 0;
+}
+
+static void user_event_enabler_update(struct user_event *user)
+{
+ struct user_event_enabler *enabler;
+ struct user_event_mm *mm = user_event_mm_get_all(user);
+ struct user_event_mm *next;
+
+ while (mm) {
+ next = mm->next;
+ mmap_read_lock(mm->mm);
+ rcu_read_lock();
+
+ list_for_each_entry_rcu(enabler, &mm->enablers, link)
+ if (enabler->event == user)
+ user_event_enabler_write(mm, enabler);
+
+ rcu_read_unlock();
+ mmap_read_unlock(mm->mm);
+ user_event_mm_put(mm);
+ mm = next;
+ }
+}
+
+static bool user_event_enabler_dup(struct user_event_enabler *orig,
+ struct user_event_mm *mm)
+{
+ struct user_event_enabler *enabler;
+
+ enabler = kzalloc(sizeof(*enabler), GFP_NOWAIT);
+
+ if (!enabler)
+ return false;
+
+ enabler->event = orig->event;
+ enabler->addr = orig->addr;
+
+ /* Only dup part of value (ignore future flags, etc) */
+ enabler->values = orig->values & ENABLE_VAL_DUP_MASK;
+
+ refcount_inc(&enabler->event->refcnt);
+ list_add_rcu(&enabler->link, &mm->enablers);
+
+ return true;
+}
+
+static struct user_event_mm *user_event_mm_get(struct user_event_mm *mm)
+{
+ refcount_inc(&mm->refcnt);
+
+ return mm;
+}
+
+static struct user_event_mm *user_event_mm_get_all(struct user_event *user)
+{
+ struct user_event_mm *found = NULL;
+ struct user_event_enabler *enabler;
+ struct user_event_mm *mm;
+
+ /*
+ * We do not want to block fork/exec while enablements are being
+ * updated, so we use RCU to walk the current tasks that have used
+ * user_events ABI for 1 or more events. Each enabler found in each
+ * task that matches the event being updated has a write to reflect
+ * the kernel state back into the process. Waits/faults must not occur
+ * during this. So we scan the list under RCU for all the mm that have
+ * the event within it. This is needed because mm_read_lock() can wait.
+ * Each user mm returned has a ref inc to handle remove RCU races.
+ */
+ rcu_read_lock();
+
+ list_for_each_entry_rcu(mm, &user_event_mms, link)
+ list_for_each_entry_rcu(enabler, &mm->enablers, link)
+ if (enabler->event == user) {
+ mm->next = found;
+ found = user_event_mm_get(mm);
+ break;
+ }
+
+ rcu_read_unlock();
+
+ return found;
+}
+
+static struct user_event_mm *user_event_mm_create(struct task_struct *t)
+{
+ struct user_event_mm *user_mm;
+ unsigned long flags;
+
+ user_mm = kzalloc(sizeof(*user_mm), GFP_KERNEL);
+
+ if (!user_mm)
+ return NULL;
+
+ user_mm->mm = t->mm;
+ INIT_LIST_HEAD(&user_mm->enablers);
+ refcount_set(&user_mm->refcnt, 1);
+ refcount_set(&user_mm->tasks, 1);
+
+ spin_lock_irqsave(&user_event_mms_lock, flags);
+ list_add_rcu(&user_mm->link, &user_event_mms);
+ spin_unlock_irqrestore(&user_event_mms_lock, flags);
+
+ t->user_event_mm = user_mm;
+
+ /*
+ * The lifetime of the memory descriptor can slightly outlast
+ * the task lifetime if a ref to the user_event_mm is taken
+ * between list_del_rcu() and call_rcu(). Therefore we need
+ * to take a reference to it to ensure it can live this long
+ * under this corner case. This can also occur in clones that
+ * outlast the parent.
+ */
+ mmgrab(user_mm->mm);
+
+ return user_mm;
+}
+
+static struct user_event_mm *current_user_event_mm(void)
+{
+ struct user_event_mm *user_mm = current->user_event_mm;
+
+ if (user_mm)
+ goto inc;
+
+ user_mm = user_event_mm_create(current);
+
+ if (!user_mm)
+ goto error;
+inc:
+ refcount_inc(&user_mm->refcnt);
+error:
+ return user_mm;
+}
+
+static void user_event_mm_destroy(struct user_event_mm *mm)
+{
+ struct user_event_enabler *enabler, *next;
+
+ list_for_each_entry_safe(enabler, next, &mm->enablers, link)
+ user_event_enabler_destroy(enabler);
+
+ mmdrop(mm->mm);
+ kfree(mm);
+}
+
+static void user_event_mm_put(struct user_event_mm *mm)
+{
+ if (mm && refcount_dec_and_test(&mm->refcnt))
+ user_event_mm_destroy(mm);
+}
+
+static void delayed_user_event_mm_put(struct work_struct *work)
+{
+ struct user_event_mm *mm;
+
+ mm = container_of(to_rcu_work(work), struct user_event_mm, put_rwork);
+ user_event_mm_put(mm);
+}
+
+void user_event_mm_remove(struct task_struct *t)
{
- int i = user->index;
+ struct user_event_mm *mm;
+ unsigned long flags;
+
+ might_sleep();
+
+ mm = t->user_event_mm;
+ t->user_event_mm = NULL;
+
+ /* Clone will increment the tasks, only remove if last clone */
+ if (!refcount_dec_and_test(&mm->tasks))
+ return;
+
+ /* Remove the mm from the list, so it can no longer be enabled */
+ spin_lock_irqsave(&user_event_mms_lock, flags);
+ list_del_rcu(&mm->link);
+ spin_unlock_irqrestore(&user_event_mms_lock, flags);
+
+ /*
+ * We need to wait for currently occurring writes to stop within
+ * the mm. This is required since exit_mm() snaps the current rss
+ * stats and clears them. On the final mmdrop(), check_mm() will
+ * report a bug if these increment.
+ *
+ * All writes/pins are done under mmap_read lock, take the write
+ * lock to ensure in-progress faults have completed. Faults that
+ * are pending but yet to run will check the task count and skip
+ * the fault since the mm is going away.
+ */
+ mmap_write_lock(mm->mm);
+ mmap_write_unlock(mm->mm);

- user->group->register_page_data[MAP_STATUS_BYTE(i)] |= MAP_STATUS_MASK(i);
+ /*
+ * Put for mm must be done after RCU delay to handle new refs in
+ * between the list_del_rcu() and now. This ensures any get refs
+ * during rcu_read_lock() are accounted for during list removal.
+ *
+ * CPU A | CPU B
+ * ---------------------------------------------------------------
+ * user_event_mm_remove() | rcu_read_lock();
+ * list_del_rcu() | list_for_each_entry_rcu();
+ * call_rcu() | refcount_inc();
+ * . | rcu_read_unlock();
+ * schedule_work() | .
+ * user_event_mm_put() | .
+ *
+ * mmdrop() cannot be called in the softirq context of call_rcu()
+ * so we use a work queue after call_rcu() to run within.
+ */
+ INIT_RCU_WORK(&mm->put_rwork, delayed_user_event_mm_put);
+ queue_rcu_work(system_wq, &mm->put_rwork);
}

-static __always_inline
-void user_event_register_clear(struct user_event *user)
+void user_event_mm_dup(struct task_struct *t, struct user_event_mm *old_mm)
{
- int i = user->index;
+ struct user_event_mm *mm = user_event_mm_create(t);
+ struct user_event_enabler *enabler;

- user->group->register_page_data[MAP_STATUS_BYTE(i)] &= ~MAP_STATUS_MASK(i);
+ if (!mm)
+ return;
+
+ rcu_read_lock();
+
+ list_for_each_entry_rcu(enabler, &old_mm->enablers, link)
+ if (!user_event_enabler_dup(enabler, mm))
+ goto error;
+
+ rcu_read_unlock();
+
+ return;
+error:
+ rcu_read_unlock();
+ user_event_mm_remove(t);
+}
+
+static struct user_event_enabler
+*user_event_enabler_create(struct user_reg *reg, struct user_event *user,
+ int *write_result)
+{
+ struct user_event_enabler *enabler;
+ struct user_event_mm *user_mm;
+ unsigned long uaddr = (unsigned long)reg->enable_addr;
+
+ user_mm = current_user_event_mm();
+
+ if (!user_mm)
+ return NULL;
+
+ enabler = kzalloc(sizeof(*enabler), GFP_KERNEL);
+
+ if (!enabler)
+ goto out;
+
+ enabler->event = user;
+ enabler->addr = uaddr;
+ enabler->values = reg->enable_bit;
+retry:
+ /* Prevents state changes from racing with new enablers */
+ mutex_lock(&event_mutex);
+
+ /* Attempt to reflect the current state within the process */
+ mmap_read_lock(user_mm->mm);
+ *write_result = user_event_enabler_write(user_mm, enabler);
+ mmap_read_unlock(user_mm->mm);
+
+ /*
+ * If the write works, then we will track the enabler. A ref to the
+ * underlying user_event is held by the enabler to prevent it going
+ * away while the enabler is still in use by a process. The ref is
+ * removed when the enabler is destroyed. This means a event cannot
+ * be forcefully deleted from the system until all tasks using it
+ * exit or run exec(), which includes forks and clones.
+ */
+ if (!*write_result) {
+ refcount_inc(&enabler->event->refcnt);
+ list_add_rcu(&enabler->link, &user_mm->enablers);
+ }
+
+ mutex_unlock(&event_mutex);
+
+ if (*write_result) {
+ /* Attempt to fault-in and retry if it worked */
+ if (!user_event_mm_fault_in(user_mm, uaddr))
+ goto retry;
+
+ kfree(enabler);
+ enabler = NULL;
+ }
+out:
+ user_event_mm_put(user_mm);
+
+ return enabler;
}

static __always_inline __must_check
@@ -824,9 +1136,6 @@ static int destroy_user_event(struct user_event *user)
return ret;

dyn_event_remove(&user->devent);
-
- user_event_register_clear(user);
- clear_bit(user->index, user->group->page_bitmap);
hash_del(&user->node);

user_event_destroy_validators(user);
@@ -972,9 +1281,9 @@ static void user_event_perf(struct user_event *user, struct iov_iter *i,
#endif

/*
- * Update the register page that is shared between user processes.
+ * Update the enabled bit among all user processes.
*/
-static void update_reg_page_for(struct user_event *user)
+static void update_enable_bit_for(struct user_event *user)
{
struct tracepoint *tp = &user->tracepoint;
char status = 0;
@@ -1005,12 +1314,9 @@ static void update_reg_page_for(struct user_event *user)
rcu_read_unlock_sched();
}

- if (status)
- user_event_register_set(user);
- else
- user_event_register_clear(user);
-
user->status = status;
+
+ user_event_enabler_update(user);
}

/*
@@ -1067,10 +1373,10 @@ static int user_event_reg(struct trace_event_call *call,
return ret;
inc:
refcount_inc(&user->refcnt);
- update_reg_page_for(user);
+ update_enable_bit_for(user);
return 0;
dec:
- update_reg_page_for(user);
+ update_enable_bit_for(user);
refcount_dec(&user->refcnt);
return 0;
}
@@ -1266,7 +1572,6 @@ static int user_event_parse(struct user_event_group *group, char *name,
struct user_event **newuser)
{
int ret;
- int index;
u32 key;
struct user_event *user;

@@ -1285,11 +1590,6 @@ static int user_event_parse(struct user_event_group *group, char *name,
return 0;
}

- index = find_first_zero_bit(group->page_bitmap, MAX_EVENTS);
-
- if (index == MAX_EVENTS)
- return -EMFILE;
-
user = kzalloc(sizeof(*user), GFP_KERNEL);

if (!user)
@@ -1335,14 +1635,11 @@ static int user_event_parse(struct user_event_group *group, char *name,
if (ret)
goto put_user_lock;

- user->index = index;
-
/* Ensure we track self ref and caller ref (2) */
refcount_set(&user->refcnt, 2);

dyn_event_init(&user->devent, &user_event_dops);
dyn_event_add(&user->devent, &user->call);
- set_bit(user->index, group->page_bitmap);
hash_add(group->register_table, &user->node, key);

mutex_unlock(&event_mutex);
@@ -1559,6 +1856,37 @@ static long user_reg_get(struct user_reg __user *ureg, struct user_reg *kreg)
if (ret)
return ret;

+ /* Ensure no flags, since we don't support any yet */
+ if (kreg->flags != 0)
+ return -EINVAL;
+
+ /* Ensure supported size */
+ switch (kreg->enable_size) {
+ case 4:
+ /* 32-bit */
+ break;
+#if BITS_PER_LONG >= 64
+ case 8:
+ /* 64-bit */
+ break;
+#endif
+ default:
+ return -EINVAL;
+ }
+
+ /* Ensure natural alignment */
+ if (kreg->enable_addr % kreg->enable_size)
+ return -EINVAL;
+
+ /* Ensure bit range for size */
+ if (kreg->enable_bit > (kreg->enable_size * BITS_PER_BYTE) - 1)
+ return -EINVAL;
+
+ /* Ensure accessible */
+ if (!access_ok((const void __user *)(uintptr_t)kreg->enable_addr,
+ kreg->enable_size))
+ return -EFAULT;
+
kreg->size = size;

return 0;
@@ -1573,8 +1901,10 @@ static long user_events_ioctl_reg(struct user_event_file_info *info,
struct user_reg __user *ureg = (struct user_reg __user *)uarg;
struct user_reg reg;
struct user_event *user;
+ struct user_event_enabler *enabler;
char *name;
long ret;
+ int write_result;

ret = user_reg_get(ureg, &reg);

@@ -1605,8 +1935,28 @@ static long user_events_ioctl_reg(struct user_event_file_info *info,
if (ret < 0)
return ret;

+ /*
+ * user_events_ref_add succeeded:
+ * At this point we have a user_event, it's lifetime is bound by the
+ * reference count, not this file. If anything fails, the user_event
+ * still has a reference until the file is released. During release
+ * any remaining references (from user_events_ref_add) are decremented.
+ *
+ * Attempt to create an enabler, which too has a lifetime tied in the
+ * same way for the event. Once the task that caused the enabler to be
+ * created exits or issues exec() then the enablers it has created
+ * will be destroyed and the ref to the event will be decremented.
+ */
+ enabler = user_event_enabler_create(&reg, user, &write_result);
+
+ if (!enabler)
+ return -ENOMEM;
+
+ /* Write failed/faulted, give error back to caller */
+ if (write_result)
+ return write_result;
+
put_user((u32)ret, &ureg->write_index);
- put_user(user->index, &ureg->status_bit);

return 0;
}
@@ -1720,38 +2070,6 @@ static const struct file_operations user_data_fops = {
.release = user_events_release,
};

-static struct user_event_group *user_status_group(struct file *file)
-{
- struct seq_file *m = file->private_data;
-
- if (!m)
- return NULL;
-
- return m->private;
-}
-
-/*
- * Maps the shared page into the user process for checking if event is enabled.
- */
-static int user_status_mmap(struct file *file, struct vm_area_struct *vma)
-{
- char *pages;
- struct user_event_group *group = user_status_group(file);
- unsigned long size = vma->vm_end - vma->vm_start;
-
- if (size != MAX_BYTES)
- return -EINVAL;
-
- if (!group)
- return -EINVAL;
-
- pages = group->register_page_data;
-
- return remap_pfn_range(vma, vma->vm_start,
- virt_to_phys(pages) >> PAGE_SHIFT,
- size, vm_get_page_prot(VM_READ));
-}
-
static void *user_seq_start(struct seq_file *m, loff_t *pos)
{
if (*pos)
@@ -1775,7 +2093,7 @@ static int user_seq_show(struct seq_file *m, void *p)
struct user_event_group *group = m->private;
struct user_event *user;
char status;
- int i, active = 0, busy = 0, flags;
+ int i, active = 0, busy = 0;

if (!group)
return -EINVAL;
@@ -1784,11 +2102,10 @@ static int user_seq_show(struct seq_file *m, void *p)

hash_for_each(group->register_table, i, user, node) {
status = user->status;
- flags = user->flags;

- seq_printf(m, "%d:%s", user->index, EVENT_NAME(user));
+ seq_printf(m, "%s", EVENT_NAME(user));

- if (flags != 0 || status != 0)
+ if (status != 0)
seq_puts(m, " #");

if (status != 0) {
@@ -1811,7 +2128,6 @@ static int user_seq_show(struct seq_file *m, void *p)
seq_puts(m, "\n");
seq_printf(m, "Active: %d\n", active);
seq_printf(m, "Busy: %d\n", busy);
- seq_printf(m, "Max: %ld\n", MAX_EVENTS);

return 0;
}
@@ -1847,7 +2163,6 @@ static int user_status_open(struct inode *node, struct file *file)

static const struct file_operations user_status_fops = {
.open = user_status_open,
- .mmap = user_status_mmap,
.read = seq_read,
.llseek = seq_lseek,
.release = seq_release,
@@ -1868,8 +2183,7 @@ static int create_user_tracefs(void)
goto err;
}

- /* mmap with MAP_SHARED requires writable fd */
- emmap = tracefs_create_file("user_events_status", TRACE_MODE_WRITE,
+ emmap = tracefs_create_file("user_events_status", TRACE_MODE_READ,
NULL, NULL, &user_status_fops);

if (!emmap) {
--
2.25.1

2023-02-21 21:12:47

by Beau Belgrave

[permalink] [raw]

Subject: [PATCH v8 09/11] tracing/user_events: Update documentation for ABI

The ABI for user_events has changed from mmap() based to remote writes.
Update the documentation to reflect these changes, add new section for
unregistering events since lifetime is now tied to tasks instead of
files.

Signed-off-by: Beau Belgrave <[email protected]>
---
Documentation/trace/user_events.rst | 177 ++++++++++++++++------------
1 file changed, 102 insertions(+), 75 deletions(-)

diff --git a/Documentation/trace/user_events.rst b/Documentation/trace/user_events.rst
index 9f181f342a70..0180714f10e3 100644
--- a/Documentation/trace/user_events.rst
+++ b/Documentation/trace/user_events.rst
@@ -11,20 +11,19 @@ that can be viewed via existing tools, such as ftrace and perf.
To enable this feature, build your kernel with CONFIG_USER_EVENTS=y.

Programs can view status of the events via
-/sys/kernel/debug/tracing/user_events_status and can both register and write
-data out via /sys/kernel/debug/tracing/user_events_data.
+/sys/kernel/tracing/user_events_status and can both register and write
+data out via /sys/kernel/tracing/user_events_data.

-Programs can also use /sys/kernel/debug/tracing/dynamic_events to register and
+Programs can also use /sys/kernel/tracing/dynamic_events to register and
delete user based events via the u: prefix. The format of the command to
dynamic_events is the same as the ioctl with the u: prefix applied.

Typically programs will register a set of events that they wish to expose to
tools that can read trace_events (such as ftrace and perf). The registration
-process gives back two ints to the program for each event. The first int is
-the status bit. This describes which bit in little-endian format in the
-/sys/kernel/debug/tracing/user_events_status file represents this event. The
-second int is the write index which describes the data when a write() or
-writev() is called on the /sys/kernel/debug/tracing/user_events_data file.
+process tells the kernel which address and bit to reflect if any tool has
+enabled the event and data should be written. The registration will give back
+a write index which describes the data when a write() or writev() is called
+on the /sys/kernel/tracing/user_events_data file.

The structures referenced in this document are contained within the
/include/uapi/linux/user_events.h file in the source tree.
@@ -35,29 +34,70 @@ filesystem and may be mounted at different paths than above.*
Registering
-----------
Registering within a user process is done via ioctl() out to the
-/sys/kernel/debug/tracing/user_events_data file. The command to issue is
+/sys/kernel/tracing/user_events_data file. The command to issue is
DIAG_IOCSREG.

This command takes a packed struct user_reg as an argument::

struct user_reg {
- u32 size;
- u64 name_args;
- u32 status_bit;
- u32 write_index;
- };
+ /* Input: Size of the user_reg structure being used */
+ __u32 size;
+
+ /* Input: Bit in enable address to use */
+ __u8 enable_bit;
+
+ /* Input: Enable size in bytes at address */
+ __u8 enable_size;
+
+ /* Input: Flags for future use, set to 0 */
+ __u16 flags;
+
+ /* Input: Address to update when enabled */
+ __u64 enable_addr;
+
+ /* Input: Pointer to string with event name, description and flags */
+ __u64 name_args;
+
+ /* Output: Index of the event to use when writing data */
+ __u32 write_index;
+ } __attribute__((__packed__));
+
+The struct user_reg requires all the above inputs to be set appropriately.

-The struct user_reg requires two inputs, the first is the size of the structure
-to ensure forward and backward compatibility. The second is the command string
-to issue for registering. Upon success two outputs are set, the status bit
-and the write index.
++ size: This must be set to sizeof(struct user_reg).
+
++ enable_bit: The bit to reflect the event status at the address specified by
+ enable_addr.
+
++ enable_size: The size of the value specified by enable_addr.
+ This must be 4 (32-bit) or 8 (64-bit). 64-bit values are only allowed to be
+ used on 64-bit kernels, however, 32-bit can be used on all kernels.
+
++ flags: The flags to use, if any. For the initial version this must be 0.
+ Callers should first attempt to use flags and retry without flags to ensure
+ support for lower versions of the kernel. If a flag is not supported -EINVAL
+ is returned.
+
++ enable_addr: The address of the value to use to reflect event status. This
+ must be naturally aligned and write accessible within the user program.
+
++ name_args: The name and arguments to describe the event, see command format
+ for details.
+
+Upon successful registration the following is set.
+
++ write_index: The index to use for this file descriptor that represents this
+ event when writing out data. The index is unique to this instance of the file
+ descriptor that was used for the registration. See writing data for details.

User based events show up under tracefs like any other event under the
subsystem named "user_events". This means tools that wish to attach to the
-events need to use /sys/kernel/debug/tracing/events/user_events/[name]/enable
+events need to use /sys/kernel/tracing/events/user_events/[name]/enable
or perf record -e user_events:[name] when attaching/recording.

-**NOTE:** *The write_index returned is only valid for the FD that was used*
+**NOTE:** The event subsystem name by default is "user_events". Callers should
+not assume it will always be "user_events". Operators reserve the right in the
+future to change the subsystem name per-process to accomodate event isolation.

Command Format
^^^^^^^^^^^^^^
@@ -94,9 +134,9 @@ Would be represented by the following field::
struct mytype myname 20

Deleting
------------
+--------
Deleting an event from within a user process is done via ioctl() out to the
-/sys/kernel/debug/tracing/user_events_data file. The command to issue is
+/sys/kernel/tracing/user_events_data file. The command to issue is
DIAG_IOCSDEL.

This command only requires a single string specifying the event to delete by
@@ -104,92 +144,79 @@ its name. Delete will only succeed if there are no references left to the
event (in both user and kernel space). User programs should use a separate file
to request deletes than the one used for registration due to this.

-Status
-------
-When tools attach/record user based events the status of the event is updated
-in realtime. This allows user programs to only incur the cost of the write() or
-writev() calls when something is actively attached to the event.
-
-User programs call mmap() on /sys/kernel/debug/tracing/user_events_status to
-check the status for each event that is registered. The bit to check in the
-file is given back after the register ioctl() via user_reg.status_bit. The bit
-is always in little-endian format. Programs can check if the bit is set either
-using a byte-wise index with a mask or a long-wise index with a little-endian
-mask.
-
-Currently the size of user_events_status is a single page, however, custom
-kernel configurations can change this size to allow more user based events. In
-all cases the size of the file is a multiple of a page size.
+Unregistering
+-------------
+If after registering an event it is no longer wanted to be updated then it can
+be disabled via ioctl() out to the /sys/kernel/tracing/user_events_data file.
+The command to issue is DIAG_IOCSUNREG. This is different than deleting, where
+deleting actually removes the event from the system. Unregistering simply tells
+the kernel your process is no longer interested in updates to the event.

-For example, if the register ioctl() gives back a status_bit of 3 you would
-check byte 0 (3 / 8) of the returned mmap data and then AND the result with 8
-(1 << (3 % 8)) to see if anything is attached to that event.
+This command takes a packed struct user_unreg as an argument::

-A byte-wise index check is performed as follows::
+ struct user_unreg {
+ /* Input: Size of the user_unreg structure being used */
+ __u32 size;

- int index, mask;
- char *status_page;
+ /* Input: Bit to unregister */
+ __u8 disable_bit;

- index = status_bit / 8;
- mask = 1 << (status_bit % 8);
+ /* Input: Reserved, set to 0 */
+ __u8 __reserved;

- ...
+ /* Input: Reserved, set to 0 */
+ __u16 __reserved2;

- if (status_page[index] & mask) {
- /* Enabled */
- }
+ /* Input: Address to unregister */
+ __u64 disable_addr;
+ } __attribute__((__packed__));

-A long-wise index check is performed as follows::
+The struct user_unreg requires all the above inputs to be set appropriately.

- #include <asm/bitsperlong.h>
- #include <endian.h>
++ size: This must be set to sizeof(struct user_unreg).

- #if __BITS_PER_LONG == 64
- #define endian_swap(x) htole64(x)
- #else
- #define endian_swap(x) htole32(x)
- #endif
++ disable_bit: This must be set to the bit to disable (same bit that was
+ previously registered via enable_bit).

- long index, mask, *status_page;
++ disable_addr: This must be set to the address to disable (same address that was
+ previously registered via enable_addr).

- index = status_bit / __BITS_PER_LONG;
- mask = 1L << (status_bit % __BITS_PER_LONG);
- mask = endian_swap(mask);
+**NOTE:** Events are automatically unregistered when execve() is invoked. During
+fork() the registered events will be retained and must be unregistered manually
+in each process if wanted.

- ...
+Status
+------
+When tools attach/record user based events the status of the event is updated
+in realtime. This allows user programs to only incur the cost of the write() or
+writev() calls when something is actively attached to the event.

- if (status_page[index] & mask) {
- /* Enabled */
- }
+The kernel will update the specified bit that was registered for the event as
+tools attach/detach from the event. User programs simply check if the bit is set
+to see if something is attached or not.

Administrators can easily check the status of all registered events by reading
the user_events_status file directly via a terminal. The output is as follows::

- Byte:Name [# Comments]
+ Name [# Comments]
...

Active: ActiveCount
Busy: BusyCount
- Max: MaxCount

For example, on a system that has a single event the output looks like this::

- 1:test
+ test

Active: 1
Busy: 0
- Max: 32768

If a user enables the user event via ftrace, the output would change to this::

- 1:test # Used by ftrace
+ test # Used by ftrace

Active: 1
Busy: 1
- Max: 32768
-
-**NOTE:** *A status bit of 0 will never be returned. This allows user programs
-to have a bit that can be used on error cases.*

Writing Data
------------
--
2.25.1

2023-02-21 21:12:47

by Beau Belgrave

[permalink] [raw]

Subject: [PATCH v8 11/11] tracing/user_events: Limit global user_event count

Operators want to be able to ensure enough tracepoints exist on the
system for kernel components as well as for user components. Since there
are only up to 64K events, by default allow up to half to be used by
user events.

Add a boot parameter (user_events_max=%d) and a kernel sysctl parameter
(kernel.user_events_max) to set a global limit that is honored among all
groups on the system. This ensures hard limits can be setup to prevent
user processes from consuming all event IDs on the system.

Signed-off-by: Beau Belgrave <[email protected]>
---
kernel/trace/trace_events_user.c | 59 ++++++++++++++++++++++++++++++++
1 file changed, 59 insertions(+)

diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index 222f2eb59c7c..6a5ebe243999 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -20,6 +20,7 @@
#include <linux/types.h>
#include <linux/uaccess.h>
#include <linux/highmem.h>
+#include <linux/init.h>
#include <linux/user_events.h>
#include "trace.h"
#include "trace_dynevent.h"
@@ -61,6 +62,12 @@ struct user_event_group {
/* Group for init_user_ns mapping, top-most group */
static struct user_event_group *init_group;

+/* Max allowed events for the whole system */
+static unsigned int max_user_events = 32768;
+
+/* Current number of events on the whole system */
+static unsigned int current_user_events;
+
/*
* Stores per-event properties, as users register events
* within a file a user_event might be created if it does not
@@ -1241,6 +1248,8 @@ static int destroy_user_event(struct user_event *user)
{
int ret = 0;

+ lockdep_assert_held(&event_mutex);
+
/* Must destroy fields before call removal */
user_event_destroy_fields(user);

@@ -1257,6 +1266,11 @@ static int destroy_user_event(struct user_event *user)
kfree(EVENT_NAME(user));
kfree(user);

+ if (current_user_events > 0)
+ current_user_events--;
+ else
+ pr_alert("BUG: Bad current_user_events\n");
+
return ret;
}

@@ -1744,6 +1758,11 @@ static int user_event_parse(struct user_event_group *group, char *name,

mutex_lock(&event_mutex);

+ if (current_user_events >= max_user_events) {
+ ret = -EMFILE;
+ goto put_user_lock;
+ }
+
ret = user_event_trace_register(user);

if (ret)
@@ -1755,6 +1774,7 @@ static int user_event_parse(struct user_event_group *group, char *name,
dyn_event_init(&user->devent, &user_event_dops);
dyn_event_add(&user->devent, &user->call);
hash_add(group->register_table, &user->node, key);
+ current_user_events++;

mutex_unlock(&event_mutex);

@@ -2386,6 +2406,43 @@ static int create_user_tracefs(void)
return -ENODEV;
}

+static int __init set_max_user_events(char *str)
+{
+ if (!str)
+ return 0;
+
+ if (kstrtouint(str, 0, &max_user_events))
+ return 0;
+
+ return 1;
+}
+__setup("user_events_max=", set_max_user_events);
+
+static int set_max_user_events_sysctl(struct ctl_table *table, int write,
+ void *buffer, size_t *lenp, loff_t *ppos)
+{
+ int ret;
+
+ mutex_lock(&event_mutex);
+
+ ret = proc_douintvec(table, write, buffer, lenp, ppos);
+
+ mutex_unlock(&event_mutex);
+
+ return ret;
+}
+
+static struct ctl_table user_event_sysctls[] = {
+ {
+ .procname = "user_events_max",
+ .data = &max_user_events,
+ .maxlen = sizeof(unsigned int),
+ .mode = 0644,
+ .proc_handler = set_max_user_events_sysctl,
+ },
+ {}
+};
+
static int __init trace_events_user_init(void)
{
int ret;
@@ -2415,6 +2472,8 @@ static int __init trace_events_user_init(void)
if (dyn_event_register(&user_event_dops))
pr_warn("user_events could not register with dyn_events\n");

+ register_sysctl_init("kernel", user_event_sysctls);
+
return 0;
}

--
2.25.1

2023-03-24 00:07:59

by Masami Hiramatsu

[permalink] [raw]

Subject: Re: [PATCH v8 00/11] tracing/user_events: Remote write ABI

Hi Beau,

Sorry for replying so late.
I reviewed the series and I think it looks good to me.
This direction is good from the user/kernel interaction viewpoint.
I have just a couple of comments, and reply to the each mail.

Thank you!

On Tue, 21 Feb 2023 13:11:32 -0800
Beau Belgrave <[email protected]> wrote:

> As part of the discussions for user_events aligned with user space
> tracers, it was determined that user programs should register a aligned
> value to set or clear a bit when an event becomes enabled. Currently a
> shared page is being used that requires mmap(). Remove the shared page
> implementation and move to a user registered address implementation.
>
> In this new model during the event registration from user programs 3 new
> values are specified. The first is the address to update when the event
> is either enabled or disabled. The second is the bit to set/clear to
> reflect the event being enabled. The third is the size of the value at
> the specified address.
>
> This allows for a local 32/64-bit value in user programs to support
> both kernel and user tracers. As an example, setting bit 31 for kernel
> tracers when the event becomes enabled allows for user tracers to use
> the other bits for ref counts or other flags. The kernel side updates
> the bit atomically, user programs need to also update these values
> atomically.
>
> User provided addresses must be aligned on a natural boundary, this
> allows for single page checking and prevents odd behaviors such as a
> enable value straddling 2 pages instead of a single page.
>
> When page faults are encountered they are done asyncly via a workqueue.
> If the page faults back in, the write update is attempted again. If the
> page cannot fault-in, then we log and wait until the next time the event
> is enabled/disabled. This is to prevent possible infinite loops resulting
> from bad user processes unmapping or changing protection values after
> registering the address.
>
> Change history
>
> V8:
> Rebase to 6.2-rc8.
>
> V7:
> Rebase to 6.2-rc4.
>
> Added flags to register ioctl, validates it's 0 for now. Future patches
> will enable other types of formats/options as needed.
>
> V6:
> Rebase to 6.2-rc2.
>
> Fixed small typos, code style.
>
> Changed from synchronize_rcu() to queue_rcu_work() to allow an rcu
> delay asyncly when mm is being removed and in an appropriate context
> for mmdrop().
>
> V5:
> GFP_NOWAIT is still needed in user_event_enabler_dup(), due to rcu lock.
>
> V4:
> Rebase to 6.1-rc7.
>
> Moved user_events_fork() out of task signal lock and dropped use of
> GFP_NOWAIT. All allocations are now GFP_KERNEL or GFP_KERNEL_ACCOUNT.
>
> Added boot parameter user_events_max= to limit global events.
>
> Added sysctl value kernel.user_events_max to limit global events.
>
> Added cgroup tracking of memory allocated for events.
>
> V3:
> Rebase to 6.1-rc6.
>
> Removed RFC tag on series.
>
> Updated documentation to reflect ABI changes.
>
> Added self-test for ABI specific clone/fork cases.
>
> Moved user_event_mm removal into do_exit() to ensure RSS task accounting
> is done properly in async fault paths. Also lets us remove the delayed
> mmdrop(), saving memory in each user_event_mm struct.
>
> Fixed timing window where task exits, but write could be in-progress.
> During exit we now take mmap_write_lock to ensure we drain writes.
>
> V2:
> Rebase to 6.1-rc5.
>
> Added various comments based on feedback.
>
> Added enable_size to register struct, allows 32/64 bit addresses
> as long as the enable_bit fits and the address is naturally aligned.
>
> Changed user_event_enabler_write to accept a new flag indicating if a
> fault fixup should be done or not. This allows user_event_enabler_create
> to return back failures to the user ioctl reg call and retry to fault
> in data.
>
> Added tracking fork/exec/exit of tasks to have the user_event_mm lifetime
> tied more to the task than the file. This came with extra requirements
> around when you can lock, such as softirq cases, as well as a RCU
> pattern to ensure fork/exec/exit take minimal lock times.
>
> Changed enablers to use a single word-aligned value for saving the bit
> to set and any flags, such as faulting asyncly or being freed. This was
> required to ensure atomic bit set/test for fork cases where taking the
> event_mutex is not a good scalability decision.
>
> Added unregister IOCTL, since file lifetime no longer limits the enable
> time for any events (the mm does).
>
> Updated sample code to reflect the new remote write based ABI.
>
> Updated self-test code to reflect the new remote write based ABI.
>
> Beau Belgrave (11):
> tracing/user_events: Split header into uapi and kernel
> tracing/user_events: Track fork/exec/exit for mm lifetime
> tracing/user_events: Use remote writes for event enablement
> tracing/user_events: Fixup enable faults asyncly
> tracing/user_events: Add ioctl for disabling addresses
> tracing/user_events: Update self-tests to write ABI
> tracing/user_events: Add ABI self-test
> tracing/user_events: Use write ABI in example
> tracing/user_events: Update documentation for ABI
> tracing/user_events: Charge event allocs to cgroups
> tracing/user_events: Limit global user_event count
>
> Documentation/trace/user_events.rst | 177 ++--
> fs/exec.c | 2 +
> include/linux/sched.h | 5 +
> include/linux/user_events.h | 101 +-
> include/uapi/linux/user_events.h | 81 ++
> kernel/exit.c | 2 +
> kernel/fork.c | 2 +
> kernel/trace/Kconfig | 5 +-
> kernel/trace/trace_events_user.c | 863 +++++++++++++++---
> samples/user_events/example.c | 47 +-
> tools/testing/selftests/user_events/Makefile | 2 +-
> .../testing/selftests/user_events/abi_test.c | 226 +++++
> .../testing/selftests/user_events/dyn_test.c | 2 +-
> .../selftests/user_events/ftrace_test.c | 162 ++--
> .../testing/selftests/user_events/perf_test.c | 39 +-
> 15 files changed, 1317 insertions(+), 399 deletions(-)
> create mode 100644 include/uapi/linux/user_events.h
> create mode 100644 tools/testing/selftests/user_events/abi_test.c
>
>
> base-commit: ceaa837f96adb69c0df0397937cd74991d5d821a
> --
> 2.25.1
>

--
Masami Hiramatsu (Google) <[email protected]>

2023-03-24 00:08:04

by Masami Hiramatsu

[permalink] [raw]

Subject: Re: [PATCH v8 09/11] tracing/user_events: Update documentation for ABI

Hi Beau,

On Tue, 21 Feb 2023 13:11:41 -0800
Beau Belgrave <[email protected]> wrote:

> The ABI for user_events has changed from mmap() based to remote writes.
> Update the documentation to reflect these changes, add new section for
> unregistering events since lifetime is now tied to tasks instead of
> files.

Thanks for updating the document. This is good. And I would like to
ask you to update one more thing in the document.

In "the Writing Data" Section,

-----
For example, if I have a struct like this::

struct payload {
int src;
int dst;
int flags;
};
-----

This payload has to be packed too.

This may be a split patch as a fix because it is not related to this
series.

Thank you,

>
> Signed-off-by: Beau Belgrave <[email protected]>
> ---
> Documentation/trace/user_events.rst | 177 ++++++++++++++++------------
> 1 file changed, 102 insertions(+), 75 deletions(-)
>
> diff --git a/Documentation/trace/user_events.rst b/Documentation/trace/user_events.rst
> index 9f181f342a70..0180714f10e3 100644
> --- a/Documentation/trace/user_events.rst
> +++ b/Documentation/trace/user_events.rst
> @@ -11,20 +11,19 @@ that can be viewed via existing tools, such as ftrace and perf.
> To enable this feature, build your kernel with CONFIG_USER_EVENTS=y.
>
> Programs can view status of the events via
> -/sys/kernel/debug/tracing/user_events_status and can both register and write
> -data out via /sys/kernel/debug/tracing/user_events_data.
> +/sys/kernel/tracing/user_events_status and can both register and write
> +data out via /sys/kernel/tracing/user_events_data.
>
> -Programs can also use /sys/kernel/debug/tracing/dynamic_events to register and
> +Programs can also use /sys/kernel/tracing/dynamic_events to register and
> delete user based events via the u: prefix. The format of the command to
> dynamic_events is the same as the ioctl with the u: prefix applied.
>
> Typically programs will register a set of events that they wish to expose to
> tools that can read trace_events (such as ftrace and perf). The registration
> -process gives back two ints to the program for each event. The first int is
> -the status bit. This describes which bit in little-endian format in the
> -/sys/kernel/debug/tracing/user_events_status file represents this event. The
> -second int is the write index which describes the data when a write() or
> -writev() is called on the /sys/kernel/debug/tracing/user_events_data file.
> +process tells the kernel which address and bit to reflect if any tool has
> +enabled the event and data should be written. The registration will give back
> +a write index which describes the data when a write() or writev() is called
> +on the /sys/kernel/tracing/user_events_data file.
>
> The structures referenced in this document are contained within the
> /include/uapi/linux/user_events.h file in the source tree.
> @@ -35,29 +34,70 @@ filesystem and may be mounted at different paths than above.*
> Registering
> -----------
> Registering within a user process is done via ioctl() out to the
> -/sys/kernel/debug/tracing/user_events_data file. The command to issue is
> +/sys/kernel/tracing/user_events_data file. The command to issue is
> DIAG_IOCSREG.
>
> This command takes a packed struct user_reg as an argument::
>
> struct user_reg {
> - u32 size;
> - u64 name_args;
> - u32 status_bit;
> - u32 write_index;
> - };
> + /* Input: Size of the user_reg structure being used */
> + __u32 size;
> +
> + /* Input: Bit in enable address to use */
> + __u8 enable_bit;
> +
> + /* Input: Enable size in bytes at address */
> + __u8 enable_size;
> +
> + /* Input: Flags for future use, set to 0 */
> + __u16 flags;
> +
> + /* Input: Address to update when enabled */
> + __u64 enable_addr;
> +
> + /* Input: Pointer to string with event name, description and flags */
> + __u64 name_args;
> +
> + /* Output: Index of the event to use when writing data */
> + __u32 write_index;
> + } __attribute__((__packed__));
> +
> +The struct user_reg requires all the above inputs to be set appropriately.
>
> -The struct user_reg requires two inputs, the first is the size of the structure
> -to ensure forward and backward compatibility. The second is the command string
> -to issue for registering. Upon success two outputs are set, the status bit
> -and the write index.
> ++ size: This must be set to sizeof(struct user_reg).
> +
> ++ enable_bit: The bit to reflect the event status at the address specified by
> + enable_addr.
> +
> ++ enable_size: The size of the value specified by enable_addr.
> + This must be 4 (32-bit) or 8 (64-bit). 64-bit values are only allowed to be
> + used on 64-bit kernels, however, 32-bit can be used on all kernels.
> +
> ++ flags: The flags to use, if any. For the initial version this must be 0.
> + Callers should first attempt to use flags and retry without flags to ensure
> + support for lower versions of the kernel. If a flag is not supported -EINVAL
> + is returned.
> +
> ++ enable_addr: The address of the value to use to reflect event status. This
> + must be naturally aligned and write accessible within the user program.
> +
> ++ name_args: The name and arguments to describe the event, see command format
> + for details.
> +
> +Upon successful registration the following is set.
> +
> ++ write_index: The index to use for this file descriptor that represents this
> + event when writing out data. The index is unique to this instance of the file
> + descriptor that was used for the registration. See writing data for details.
>
> User based events show up under tracefs like any other event under the
> subsystem named "user_events". This means tools that wish to attach to the
> -events need to use /sys/kernel/debug/tracing/events/user_events/[name]/enable
> +events need to use /sys/kernel/tracing/events/user_events/[name]/enable
> or perf record -e user_events:[name] when attaching/recording.
>
> -**NOTE:** *The write_index returned is only valid for the FD that was used*
> +**NOTE:** The event subsystem name by default is "user_events". Callers should
> +not assume it will always be "user_events". Operators reserve the right in the
> +future to change the subsystem name per-process to accomodate event isolation.
>
> Command Format
> ^^^^^^^^^^^^^^
> @@ -94,9 +134,9 @@ Would be represented by the following field::
> struct mytype myname 20
>
> Deleting
> ------------
> +--------
> Deleting an event from within a user process is done via ioctl() out to the
> -/sys/kernel/debug/tracing/user_events_data file. The command to issue is
> +/sys/kernel/tracing/user_events_data file. The command to issue is
> DIAG_IOCSDEL.
>
> This command only requires a single string specifying the event to delete by
> @@ -104,92 +144,79 @@ its name. Delete will only succeed if there are no references left to the
> event (in both user and kernel space). User programs should use a separate file
> to request deletes than the one used for registration due to this.
>
> -Status
> -------
> -When tools attach/record user based events the status of the event is updated
> -in realtime. This allows user programs to only incur the cost of the write() or
> -writev() calls when something is actively attached to the event.
> -
> -User programs call mmap() on /sys/kernel/debug/tracing/user_events_status to
> -check the status for each event that is registered. The bit to check in the
> -file is given back after the register ioctl() via user_reg.status_bit. The bit
> -is always in little-endian format. Programs can check if the bit is set either
> -using a byte-wise index with a mask or a long-wise index with a little-endian
> -mask.
> -
> -Currently the size of user_events_status is a single page, however, custom
> -kernel configurations can change this size to allow more user based events. In
> -all cases the size of the file is a multiple of a page size.
> +Unregistering
> +-------------
> +If after registering an event it is no longer wanted to be updated then it can
> +be disabled via ioctl() out to the /sys/kernel/tracing/user_events_data file.
> +The command to issue is DIAG_IOCSUNREG. This is different than deleting, where
> +deleting actually removes the event from the system. Unregistering simply tells
> +the kernel your process is no longer interested in updates to the event.
>
> -For example, if the register ioctl() gives back a status_bit of 3 you would
> -check byte 0 (3 / 8) of the returned mmap data and then AND the result with 8
> -(1 << (3 % 8)) to see if anything is attached to that event.
> +This command takes a packed struct user_unreg as an argument::
>
> -A byte-wise index check is performed as follows::
> + struct user_unreg {
> + /* Input: Size of the user_unreg structure being used */
> + __u32 size;
>
> - int index, mask;
> - char *status_page;
> + /* Input: Bit to unregister */
> + __u8 disable_bit;
>
> - index = status_bit / 8;
> - mask = 1 << (status_bit % 8);
> + /* Input: Reserved, set to 0 */
> + __u8 __reserved;
>
> - ...
> + /* Input: Reserved, set to 0 */
> + __u16 __reserved2;
>
> - if (status_page[index] & mask) {
> - /* Enabled */
> - }
> + /* Input: Address to unregister */
> + __u64 disable_addr;
> + } __attribute__((__packed__));
>
> -A long-wise index check is performed as follows::
> +The struct user_unreg requires all the above inputs to be set appropriately.
>
> - #include <asm/bitsperlong.h>
> - #include <endian.h>
> ++ size: This must be set to sizeof(struct user_unreg).
>
> - #if __BITS_PER_LONG == 64
> - #define endian_swap(x) htole64(x)
> - #else
> - #define endian_swap(x) htole32(x)
> - #endif
> ++ disable_bit: This must be set to the bit to disable (same bit that was
> + previously registered via enable_bit).
>
> - long index, mask, *status_page;
> ++ disable_addr: This must be set to the address to disable (same address that was
> + previously registered via enable_addr).
>
> - index = status_bit / __BITS_PER_LONG;
> - mask = 1L << (status_bit % __BITS_PER_LONG);
> - mask = endian_swap(mask);
> +**NOTE:** Events are automatically unregistered when execve() is invoked. During
> +fork() the registered events will be retained and must be unregistered manually
> +in each process if wanted.
>
> - ...
> +Status
> +------
> +When tools attach/record user based events the status of the event is updated
> +in realtime. This allows user programs to only incur the cost of the write() or
> +writev() calls when something is actively attached to the event.
>
> - if (status_page[index] & mask) {
> - /* Enabled */
> - }
> +The kernel will update the specified bit that was registered for the event as
> +tools attach/detach from the event. User programs simply check if the bit is set
> +to see if something is attached or not.
>
> Administrators can easily check the status of all registered events by reading
> the user_events_status file directly via a terminal. The output is as follows::
>
> - Byte:Name [# Comments]
> + Name [# Comments]
> ...
>
> Active: ActiveCount
> Busy: BusyCount
> - Max: MaxCount
>
> For example, on a system that has a single event the output looks like this::
>
> - 1:test
> + test
>
> Active: 1
> Busy: 0
> - Max: 32768
>
> If a user enables the user event via ftrace, the output would change to this::
>
> - 1:test # Used by ftrace
> + test # Used by ftrace
>
> Active: 1
> Busy: 1
> - Max: 32768
> -
> -**NOTE:** *A status bit of 0 will never be returned. This allows user programs
> -to have a bit that can be used on error cases.*
>
> Writing Data
> ------------
> --
> 2.25.1
>

--
Masami Hiramatsu (Google) <[email protected]>

2023-03-24 00:20:21

by Masami Hiramatsu

[permalink] [raw]

Subject: Re: [PATCH v8 11/11] tracing/user_events: Limit global user_event count

Hi Beau,

On Tue, 21 Feb 2023 13:11:43 -0800
Beau Belgrave <[email protected]> wrote:

> Operators want to be able to ensure enough tracepoints exist on the
> system for kernel components as well as for user components. Since there
> are only up to 64K events, by default allow up to half to be used by
> user events.
>
> Add a boot parameter (user_events_max=%d) and a kernel sysctl parameter
> (kernel.user_events_max) to set a global limit that is honored among all
> groups on the system. This ensures hard limits can be setup to prevent
> user processes from consuming all event IDs on the system.

sysctl is good to me, but would we really need the kernel parameter?
The user_events starts using when user-space is up, so I think setting
the limit with sysctl is enough.

BTW, Vlastimil tried to add 'sysctl.*' kernel parameter support(*). If we
need a kernel cmdline support, I think this is more generic way. But it
seems the discussion has been stopped.

(*) https://patchwork.kernel.org/project/linux-mm/patch/[email protected]/

Thank you,

>
> Signed-off-by: Beau Belgrave <[email protected]>
> ---
> kernel/trace/trace_events_user.c | 59 ++++++++++++++++++++++++++++++++
> 1 file changed, 59 insertions(+)
>
> diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
> index 222f2eb59c7c..6a5ebe243999 100644
> --- a/kernel/trace/trace_events_user.c
> +++ b/kernel/trace/trace_events_user.c
> @@ -20,6 +20,7 @@
> #include <linux/types.h>
> #include <linux/uaccess.h>
> #include <linux/highmem.h>
> +#include <linux/init.h>
> #include <linux/user_events.h>
> #include "trace.h"
> #include "trace_dynevent.h"
> @@ -61,6 +62,12 @@ struct user_event_group {
> /* Group for init_user_ns mapping, top-most group */
> static struct user_event_group *init_group;
>
> +/* Max allowed events for the whole system */
> +static unsigned int max_user_events = 32768;
> +
> +/* Current number of events on the whole system */
> +static unsigned int current_user_events;
> +
> /*
> * Stores per-event properties, as users register events
> * within a file a user_event might be created if it does not
> @@ -1241,6 +1248,8 @@ static int destroy_user_event(struct user_event *user)
> {
> int ret = 0;
>
> + lockdep_assert_held(&event_mutex);
> +
> /* Must destroy fields before call removal */
> user_event_destroy_fields(user);
>
> @@ -1257,6 +1266,11 @@ static int destroy_user_event(struct user_event *user)
> kfree(EVENT_NAME(user));
> kfree(user);
>
> + if (current_user_events > 0)
> + current_user_events--;
> + else
> + pr_alert("BUG: Bad current_user_events\n");
> +
> return ret;
> }
>
> @@ -1744,6 +1758,11 @@ static int user_event_parse(struct user_event_group *group, char *name,
>
> mutex_lock(&event_mutex);
>
> + if (current_user_events >= max_user_events) {
> + ret = -EMFILE;
> + goto put_user_lock;
> + }
> +
> ret = user_event_trace_register(user);
>
> if (ret)
> @@ -1755,6 +1774,7 @@ static int user_event_parse(struct user_event_group *group, char *name,
> dyn_event_init(&user->devent, &user_event_dops);
> dyn_event_add(&user->devent, &user->call);
> hash_add(group->register_table, &user->node, key);
> + current_user_events++;
>
> mutex_unlock(&event_mutex);
>
> @@ -2386,6 +2406,43 @@ static int create_user_tracefs(void)
> return -ENODEV;
> }
>
> +static int __init set_max_user_events(char *str)
> +{
> + if (!str)
> + return 0;
> +
> + if (kstrtouint(str, 0, &max_user_events))
> + return 0;
> +
> + return 1;
> +}
> +__setup("user_events_max=", set_max_user_events);
> +
> +static int set_max_user_events_sysctl(struct ctl_table *table, int write,
> + void *buffer, size_t *lenp, loff_t *ppos)
> +{
> + int ret;
> +
> + mutex_lock(&event_mutex);
> +
> + ret = proc_douintvec(table, write, buffer, lenp, ppos);
> +
> + mutex_unlock(&event_mutex);
> +
> + return ret;
> +}
> +
> +static struct ctl_table user_event_sysctls[] = {
> + {
> + .procname = "user_events_max",
> + .data = &max_user_events,
> + .maxlen = sizeof(unsigned int),
> + .mode = 0644,
> + .proc_handler = set_max_user_events_sysctl,
> + },
> + {}
> +};
> +
> static int __init trace_events_user_init(void)
> {
> int ret;
> @@ -2415,6 +2472,8 @@ static int __init trace_events_user_init(void)
> if (dyn_event_register(&user_event_dops))
> pr_warn("user_events could not register with dyn_events\n");
>
> + register_sysctl_init("kernel", user_event_sysctls);
> +
> return 0;
> }
>
> --
> 2.25.1
>

--
Masami Hiramatsu (Google) <[email protected]>

2023-03-24 08:56:14

by Vlastimil Babka

[permalink] [raw]

Subject: Re: [PATCH v8 11/11] tracing/user_events: Limit global user_event count

On 3/24/23 01:18, Masami Hiramatsu (Google) wrote:
> Hi Beau,
>
> On Tue, 21 Feb 2023 13:11:43 -0800
> Beau Belgrave <[email protected]> wrote:
>
>> Operators want to be able to ensure enough tracepoints exist on the
>> system for kernel components as well as for user components. Since there
>> are only up to 64K events, by default allow up to half to be used by
>> user events.
>>
>> Add a boot parameter (user_events_max=%d) and a kernel sysctl parameter
>> (kernel.user_events_max) to set a global limit that is honored among all
>> groups on the system. This ensures hard limits can be setup to prevent
>> user processes from consuming all event IDs on the system.
>
> sysctl is good to me, but would we really need the kernel parameter?
> The user_events starts using when user-space is up, so I think setting
> the limit with sysctl is enough.
>
> BTW, Vlastimil tried to add 'sysctl.*' kernel parameter support(*). If we
> need a kernel cmdline support, I think this is more generic way. But it
> seems the discussion has been stopped.

It was actually merged in 5.8. So sysctl should be sufficient with that.
But maybe it's weird to start adding sysctls, when the rest of tracing
tunables is AFAIK under /sys/kernel/tracing/ ?

> (*) https://patchwork.kernel.org/project/linux-mm/patch/[email protected]/
>
> Thank you,
>
>>
>> Signed-off-by: Beau Belgrave <[email protected]>
>> ---
>> kernel/trace/trace_events_user.c | 59 ++++++++++++++++++++++++++++++++
>> 1 file changed, 59 insertions(+)
>>
>> diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
>> index 222f2eb59c7c..6a5ebe243999 100644
>> --- a/kernel/trace/trace_events_user.c
>> +++ b/kernel/trace/trace_events_user.c
>> @@ -20,6 +20,7 @@
>> #include <linux/types.h>
>> #include <linux/uaccess.h>
>> #include <linux/highmem.h>
>> +#include <linux/init.h>
>> #include <linux/user_events.h>
>> #include "trace.h"
>> #include "trace_dynevent.h"
>> @@ -61,6 +62,12 @@ struct user_event_group {
>> /* Group for init_user_ns mapping, top-most group */
>> static struct user_event_group *init_group;
>>
>> +/* Max allowed events for the whole system */
>> +static unsigned int max_user_events = 32768;
>> +
>> +/* Current number of events on the whole system */
>> +static unsigned int current_user_events;
>> +
>> /*
>> * Stores per-event properties, as users register events
>> * within a file a user_event might be created if it does not
>> @@ -1241,6 +1248,8 @@ static int destroy_user_event(struct user_event *user)
>> {
>> int ret = 0;
>>
>> + lockdep_assert_held(&event_mutex);
>> +
>> /* Must destroy fields before call removal */
>> user_event_destroy_fields(user);
>>
>> @@ -1257,6 +1266,11 @@ static int destroy_user_event(struct user_event *user)
>> kfree(EVENT_NAME(user));
>> kfree(user);
>>
>> + if (current_user_events > 0)
>> + current_user_events--;
>> + else
>> + pr_alert("BUG: Bad current_user_events\n");
>> +
>> return ret;
>> }
>>
>> @@ -1744,6 +1758,11 @@ static int user_event_parse(struct user_event_group *group, char *name,
>>
>> mutex_lock(&event_mutex);
>>
>> + if (current_user_events >= max_user_events) {
>> + ret = -EMFILE;
>> + goto put_user_lock;
>> + }
>> +
>> ret = user_event_trace_register(user);
>>
>> if (ret)
>> @@ -1755,6 +1774,7 @@ static int user_event_parse(struct user_event_group *group, char *name,
>> dyn_event_init(&user->devent, &user_event_dops);
>> dyn_event_add(&user->devent, &user->call);
>> hash_add(group->register_table, &user->node, key);
>> + current_user_events++;
>>
>> mutex_unlock(&event_mutex);
>>
>> @@ -2386,6 +2406,43 @@ static int create_user_tracefs(void)
>> return -ENODEV;
>> }
>>
>> +static int __init set_max_user_events(char *str)
>> +{
>> + if (!str)
>> + return 0;
>> +
>> + if (kstrtouint(str, 0, &max_user_events))
>> + return 0;
>> +
>> + return 1;
>> +}
>> +__setup("user_events_max=", set_max_user_events);
>> +
>> +static int set_max_user_events_sysctl(struct ctl_table *table, int write,
>> + void *buffer, size_t *lenp, loff_t *ppos)
>> +{
>> + int ret;
>> +
>> + mutex_lock(&event_mutex);
>> +
>> + ret = proc_douintvec(table, write, buffer, lenp, ppos);
>> +
>> + mutex_unlock(&event_mutex);
>> +
>> + return ret;
>> +}
>> +
>> +static struct ctl_table user_event_sysctls[] = {
>> + {
>> + .procname = "user_events_max",
>> + .data = &max_user_events,
>> + .maxlen = sizeof(unsigned int),
>> + .mode = 0644,
>> + .proc_handler = set_max_user_events_sysctl,
>> + },
>> + {}
>> +};
>> +
>> static int __init trace_events_user_init(void)
>> {
>> int ret;
>> @@ -2415,6 +2472,8 @@ static int __init trace_events_user_init(void)
>> if (dyn_event_register(&user_event_dops))
>> pr_warn("user_events could not register with dyn_events\n");
>>
>> + register_sysctl_init("kernel", user_event_sysctls);
>> +
>> return 0;
>> }
>>
>> --
>> 2.25.1
>>
>
>

2023-03-24 16:49:40

by Beau Belgrave

[permalink] [raw]

Subject: Re: [PATCH v8 11/11] tracing/user_events: Limit global user_event count

On Fri, Mar 24, 2023 at 09:54:48AM +0100, Vlastimil Babka wrote:
> On 3/24/23 01:18, Masami Hiramatsu (Google) wrote:
> > Hi Beau,
> >
> > On Tue, 21 Feb 2023 13:11:43 -0800
> > Beau Belgrave <[email protected]> wrote:
> >
> >> Operators want to be able to ensure enough tracepoints exist on the
> >> system for kernel components as well as for user components. Since there
> >> are only up to 64K events, by default allow up to half to be used by
> >> user events.
> >>
> >> Add a boot parameter (user_events_max=%d) and a kernel sysctl parameter
> >> (kernel.user_events_max) to set a global limit that is honored among all
> >> groups on the system. This ensures hard limits can be setup to prevent
> >> user processes from consuming all event IDs on the system.
> >
> > sysctl is good to me, but would we really need the kernel parameter?
> > The user_events starts using when user-space is up, so I think setting
> > the limit with sysctl is enough.
> >
> > BTW, Vlastimil tried to add 'sysctl.*' kernel parameter support(*). If we
> > need a kernel cmdline support, I think this is more generic way. But it
> > seems the discussion has been stopped.
>
> It was actually merged in 5.8. So sysctl should be sufficient with that.
> But maybe it's weird to start adding sysctls, when the rest of tracing
> tunables is AFAIK under /sys/kernel/tracing/ ?
>

During the TraceFS meetings Steven runs I was asked to add a boot
parameter and sysctl for user_events to limit the max.

To me, it seems when user_events moves toward namespace awareness
sysctl might be easier to use from within a namespace to turn knobs.

Happy to change to whatever, but I want to see Steven and Masami agree
on the approach before doing so.

Steven, do you agree with Masami to move to just sysctl?

Thanks,
-Beau

>
> > (*) https://patchwork.kernel.org/project/linux-mm/patch/[email protected]/
> >
> > Thank you,
> >
> >>
> >> Signed-off-by: Beau Belgrave <[email protected]>
> >> ---
> >> kernel/trace/trace_events_user.c | 59 ++++++++++++++++++++++++++++++++
> >> 1 file changed, 59 insertions(+)
> >>
> >> diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
> >> index 222f2eb59c7c..6a5ebe243999 100644
> >> --- a/kernel/trace/trace_events_user.c
> >> +++ b/kernel/trace/trace_events_user.c
> >> @@ -20,6 +20,7 @@
> >> #include <linux/types.h>
> >> #include <linux/uaccess.h>
> >> #include <linux/highmem.h>
> >> +#include <linux/init.h>
> >> #include <linux/user_events.h>
> >> #include "trace.h"
> >> #include "trace_dynevent.h"
> >> @@ -61,6 +62,12 @@ struct user_event_group {
> >> /* Group for init_user_ns mapping, top-most group */
> >> static struct user_event_group *init_group;
> >>
> >> +/* Max allowed events for the whole system */
> >> +static unsigned int max_user_events = 32768;
> >> +
> >> +/* Current number of events on the whole system */
> >> +static unsigned int current_user_events;
> >> +
> >> /*
> >> * Stores per-event properties, as users register events
> >> * within a file a user_event might be created if it does not
> >> @@ -1241,6 +1248,8 @@ static int destroy_user_event(struct user_event *user)
> >> {
> >> int ret = 0;
> >>
> >> + lockdep_assert_held(&event_mutex);
> >> +
> >> /* Must destroy fields before call removal */
> >> user_event_destroy_fields(user);
> >>
> >> @@ -1257,6 +1266,11 @@ static int destroy_user_event(struct user_event *user)
> >> kfree(EVENT_NAME(user));
> >> kfree(user);
> >>
> >> + if (current_user_events > 0)
> >> + current_user_events--;
> >> + else
> >> + pr_alert("BUG: Bad current_user_events\n");
> >> +
> >> return ret;
> >> }
> >>
> >> @@ -1744,6 +1758,11 @@ static int user_event_parse(struct user_event_group *group, char *name,
> >>
> >> mutex_lock(&event_mutex);
> >>
> >> + if (current_user_events >= max_user_events) {
> >> + ret = -EMFILE;
> >> + goto put_user_lock;
> >> + }
> >> +
> >> ret = user_event_trace_register(user);
> >>
> >> if (ret)
> >> @@ -1755,6 +1774,7 @@ static int user_event_parse(struct user_event_group *group, char *name,
> >> dyn_event_init(&user->devent, &user_event_dops);
> >> dyn_event_add(&user->devent, &user->call);
> >> hash_add(group->register_table, &user->node, key);
> >> + current_user_events++;
> >>
> >> mutex_unlock(&event_mutex);
> >>
> >> @@ -2386,6 +2406,43 @@ static int create_user_tracefs(void)
> >> return -ENODEV;
> >> }
> >>
> >> +static int __init set_max_user_events(char *str)
> >> +{
> >> + if (!str)
> >> + return 0;
> >> +
> >> + if (kstrtouint(str, 0, &max_user_events))
> >> + return 0;
> >> +
> >> + return 1;
> >> +}
> >> +__setup("user_events_max=", set_max_user_events);
> >> +
> >> +static int set_max_user_events_sysctl(struct ctl_table *table, int write,
> >> + void *buffer, size_t *lenp, loff_t *ppos)
> >> +{
> >> + int ret;
> >> +
> >> + mutex_lock(&event_mutex);
> >> +
> >> + ret = proc_douintvec(table, write, buffer, lenp, ppos);
> >> +
> >> + mutex_unlock(&event_mutex);
> >> +
> >> + return ret;
> >> +}
> >> +
> >> +static struct ctl_table user_event_sysctls[] = {
> >> + {
> >> + .procname = "user_events_max",
> >> + .data = &max_user_events,
> >> + .maxlen = sizeof(unsigned int),
> >> + .mode = 0644,
> >> + .proc_handler = set_max_user_events_sysctl,
> >> + },
> >> + {}
> >> +};
> >> +
> >> static int __init trace_events_user_init(void)
> >> {
> >> int ret;
> >> @@ -2415,6 +2472,8 @@ static int __init trace_events_user_init(void)
> >> if (dyn_event_register(&user_event_dops))
> >> pr_warn("user_events could not register with dyn_events\n");
> >>
> >> + register_sysctl_init("kernel", user_event_sysctls);
> >> +
> >> return 0;
> >> }
> >>
> >> --
> >> 2.25.1
> >>
> >
> >

2023-03-24 16:53:01

by Beau Belgrave

[permalink] [raw]

Subject: Re: [PATCH v8 09/11] tracing/user_events: Update documentation for ABI

On Fri, Mar 24, 2023 at 08:06:07AM +0800, Masami Hiramatsu wrote:
> Hi Beau,
>
> On Tue, 21 Feb 2023 13:11:41 -0800
> Beau Belgrave <[email protected]> wrote:
>
> > The ABI for user_events has changed from mmap() based to remote writes.
> > Update the documentation to reflect these changes, add new section for
> > unregistering events since lifetime is now tied to tasks instead of
> > files.
>
> Thanks for updating the document. This is good. And I would like to
> ask you to update one more thing in the document.
>
> In "the Writing Data" Section,
>
> -----
> For example, if I have a struct like this::
>
> struct payload {
> int src;
> int dst;
> int flags;
> };
> -----
>
> This payload has to be packed too.
>

Good catch, I'll add this.

> This may be a split patch as a fix because it is not related to this
> series.
>

If I spin another version for the sysctl feedback I'll include it there.
Otherwise, I'll push as a separate fix.

Thanks,
-Beau

> Thank you,
>
> >
> > Signed-off-by: Beau Belgrave <[email protected]>
> > ---
> > Documentation/trace/user_events.rst | 177 ++++++++++++++++------------
> > 1 file changed, 102 insertions(+), 75 deletions(-)
> >
> > diff --git a/Documentation/trace/user_events.rst b/Documentation/trace/user_events.rst
> > index 9f181f342a70..0180714f10e3 100644
> > --- a/Documentation/trace/user_events.rst
> > +++ b/Documentation/trace/user_events.rst
> > @@ -11,20 +11,19 @@ that can be viewed via existing tools, such as ftrace and perf.
> > To enable this feature, build your kernel with CONFIG_USER_EVENTS=y.
> >
> > Programs can view status of the events via
> > -/sys/kernel/debug/tracing/user_events_status and can both register and write
> > -data out via /sys/kernel/debug/tracing/user_events_data.
> > +/sys/kernel/tracing/user_events_status and can both register and write
> > +data out via /sys/kernel/tracing/user_events_data.
> >
> > -Programs can also use /sys/kernel/debug/tracing/dynamic_events to register and
> > +Programs can also use /sys/kernel/tracing/dynamic_events to register and
> > delete user based events via the u: prefix. The format of the command to
> > dynamic_events is the same as the ioctl with the u: prefix applied.
> >
> > Typically programs will register a set of events that they wish to expose to
> > tools that can read trace_events (such as ftrace and perf). The registration
> > -process gives back two ints to the program for each event. The first int is
> > -the status bit. This describes which bit in little-endian format in the
> > -/sys/kernel/debug/tracing/user_events_status file represents this event. The
> > -second int is the write index which describes the data when a write() or
> > -writev() is called on the /sys/kernel/debug/tracing/user_events_data file.
> > +process tells the kernel which address and bit to reflect if any tool has
> > +enabled the event and data should be written. The registration will give back
> > +a write index which describes the data when a write() or writev() is called
> > +on the /sys/kernel/tracing/user_events_data file.
> >
> > The structures referenced in this document are contained within the
> > /include/uapi/linux/user_events.h file in the source tree.
> > @@ -35,29 +34,70 @@ filesystem and may be mounted at different paths than above.*
> > Registering
> > -----------
> > Registering within a user process is done via ioctl() out to the
> > -/sys/kernel/debug/tracing/user_events_data file. The command to issue is
> > +/sys/kernel/tracing/user_events_data file. The command to issue is
> > DIAG_IOCSREG.
> >
> > This command takes a packed struct user_reg as an argument::
> >
> > struct user_reg {
> > - u32 size;
> > - u64 name_args;
> > - u32 status_bit;
> > - u32 write_index;
> > - };
> > + /* Input: Size of the user_reg structure being used */
> > + __u32 size;
> > +
> > + /* Input: Bit in enable address to use */
> > + __u8 enable_bit;
> > +
> > + /* Input: Enable size in bytes at address */
> > + __u8 enable_size;
> > +
> > + /* Input: Flags for future use, set to 0 */
> > + __u16 flags;
> > +
> > + /* Input: Address to update when enabled */
> > + __u64 enable_addr;
> > +
> > + /* Input: Pointer to string with event name, description and flags */
> > + __u64 name_args;
> > +
> > + /* Output: Index of the event to use when writing data */
> > + __u32 write_index;
> > + } __attribute__((__packed__));
> > +
> > +The struct user_reg requires all the above inputs to be set appropriately.
> >
> > -The struct user_reg requires two inputs, the first is the size of the structure
> > -to ensure forward and backward compatibility. The second is the command string
> > -to issue for registering. Upon success two outputs are set, the status bit
> > -and the write index.
> > ++ size: This must be set to sizeof(struct user_reg).
> > +
> > ++ enable_bit: The bit to reflect the event status at the address specified by
> > + enable_addr.
> > +
> > ++ enable_size: The size of the value specified by enable_addr.
> > + This must be 4 (32-bit) or 8 (64-bit). 64-bit values are only allowed to be
> > + used on 64-bit kernels, however, 32-bit can be used on all kernels.
> > +
> > ++ flags: The flags to use, if any. For the initial version this must be 0.
> > + Callers should first attempt to use flags and retry without flags to ensure
> > + support for lower versions of the kernel. If a flag is not supported -EINVAL
> > + is returned.
> > +
> > ++ enable_addr: The address of the value to use to reflect event status. This
> > + must be naturally aligned and write accessible within the user program.
> > +
> > ++ name_args: The name and arguments to describe the event, see command format
> > + for details.
> > +
> > +Upon successful registration the following is set.
> > +
> > ++ write_index: The index to use for this file descriptor that represents this
> > + event when writing out data. The index is unique to this instance of the file
> > + descriptor that was used for the registration. See writing data for details.
> >
> > User based events show up under tracefs like any other event under the
> > subsystem named "user_events". This means tools that wish to attach to the
> > -events need to use /sys/kernel/debug/tracing/events/user_events/[name]/enable
> > +events need to use /sys/kernel/tracing/events/user_events/[name]/enable
> > or perf record -e user_events:[name] when attaching/recording.
> >
> > -**NOTE:** *The write_index returned is only valid for the FD that was used*
> > +**NOTE:** The event subsystem name by default is "user_events". Callers should
> > +not assume it will always be "user_events". Operators reserve the right in the
> > +future to change the subsystem name per-process to accomodate event isolation.
> >
> > Command Format
> > ^^^^^^^^^^^^^^
> > @@ -94,9 +134,9 @@ Would be represented by the following field::
> > struct mytype myname 20
> >
> > Deleting
> > ------------
> > +--------
> > Deleting an event from within a user process is done via ioctl() out to the
> > -/sys/kernel/debug/tracing/user_events_data file. The command to issue is
> > +/sys/kernel/tracing/user_events_data file. The command to issue is
> > DIAG_IOCSDEL.
> >
> > This command only requires a single string specifying the event to delete by
> > @@ -104,92 +144,79 @@ its name. Delete will only succeed if there are no references left to the
> > event (in both user and kernel space). User programs should use a separate file
> > to request deletes than the one used for registration due to this.
> >
> > -Status
> > -------
> > -When tools attach/record user based events the status of the event is updated
> > -in realtime. This allows user programs to only incur the cost of the write() or
> > -writev() calls when something is actively attached to the event.
> > -
> > -User programs call mmap() on /sys/kernel/debug/tracing/user_events_status to
> > -check the status for each event that is registered. The bit to check in the
> > -file is given back after the register ioctl() via user_reg.status_bit. The bit
> > -is always in little-endian format. Programs can check if the bit is set either
> > -using a byte-wise index with a mask or a long-wise index with a little-endian
> > -mask.
> > -
> > -Currently the size of user_events_status is a single page, however, custom
> > -kernel configurations can change this size to allow more user based events. In
> > -all cases the size of the file is a multiple of a page size.
> > +Unregistering
> > +-------------
> > +If after registering an event it is no longer wanted to be updated then it can
> > +be disabled via ioctl() out to the /sys/kernel/tracing/user_events_data file.
> > +The command to issue is DIAG_IOCSUNREG. This is different than deleting, where
> > +deleting actually removes the event from the system. Unregistering simply tells
> > +the kernel your process is no longer interested in updates to the event.
> >
> > -For example, if the register ioctl() gives back a status_bit of 3 you would
> > -check byte 0 (3 / 8) of the returned mmap data and then AND the result with 8
> > -(1 << (3 % 8)) to see if anything is attached to that event.
> > +This command takes a packed struct user_unreg as an argument::
> >
> > -A byte-wise index check is performed as follows::
> > + struct user_unreg {
> > + /* Input: Size of the user_unreg structure being used */
> > + __u32 size;
> >
> > - int index, mask;
> > - char *status_page;
> > + /* Input: Bit to unregister */
> > + __u8 disable_bit;
> >
> > - index = status_bit / 8;
> > - mask = 1 << (status_bit % 8);
> > + /* Input: Reserved, set to 0 */
> > + __u8 __reserved;
> >
> > - ...
> > + /* Input: Reserved, set to 0 */
> > + __u16 __reserved2;
> >
> > - if (status_page[index] & mask) {
> > - /* Enabled */
> > - }
> > + /* Input: Address to unregister */
> > + __u64 disable_addr;
> > + } __attribute__((__packed__));
> >
> > -A long-wise index check is performed as follows::
> > +The struct user_unreg requires all the above inputs to be set appropriately.
> >
> > - #include <asm/bitsperlong.h>
> > - #include <endian.h>
> > ++ size: This must be set to sizeof(struct user_unreg).
> >
> > - #if __BITS_PER_LONG == 64
> > - #define endian_swap(x) htole64(x)
> > - #else
> > - #define endian_swap(x) htole32(x)
> > - #endif
> > ++ disable_bit: This must be set to the bit to disable (same bit that was
> > + previously registered via enable_bit).
> >
> > - long index, mask, *status_page;
> > ++ disable_addr: This must be set to the address to disable (same address that was
> > + previously registered via enable_addr).
> >
> > - index = status_bit / __BITS_PER_LONG;
> > - mask = 1L << (status_bit % __BITS_PER_LONG);
> > - mask = endian_swap(mask);
> > +**NOTE:** Events are automatically unregistered when execve() is invoked. During
> > +fork() the registered events will be retained and must be unregistered manually
> > +in each process if wanted.
> >
> > - ...
> > +Status
> > +------
> > +When tools attach/record user based events the status of the event is updated
> > +in realtime. This allows user programs to only incur the cost of the write() or
> > +writev() calls when something is actively attached to the event.
> >
> > - if (status_page[index] & mask) {
> > - /* Enabled */
> > - }
> > +The kernel will update the specified bit that was registered for the event as
> > +tools attach/detach from the event. User programs simply check if the bit is set
> > +to see if something is attached or not.
> >
> > Administrators can easily check the status of all registered events by reading
> > the user_events_status file directly via a terminal. The output is as follows::
> >
> > - Byte:Name [# Comments]
> > + Name [# Comments]
> > ...
> >
> > Active: ActiveCount
> > Busy: BusyCount
> > - Max: MaxCount
> >
> > For example, on a system that has a single event the output looks like this::
> >
> > - 1:test
> > + test
> >
> > Active: 1
> > Busy: 0
> > - Max: 32768
> >
> > If a user enables the user event via ftrace, the output would change to this::
> >
> > - 1:test # Used by ftrace
> > + test # Used by ftrace
> >
> > Active: 1
> > Busy: 1
> > - Max: 32768
> > -
> > -**NOTE:** *A status bit of 0 will never be returned. This allows user programs
> > -to have a bit that can be used on error cases.*
> >
> > Writing Data
> > ------------
> > --
> > 2.25.1
> >
>
>
> --
> Masami Hiramatsu (Google) <[email protected]>

2023-03-24 17:09:01

by Steven Rostedt

[permalink] [raw]

Subject: Re: [PATCH v8 11/11] tracing/user_events: Limit global user_event count

On Fri, 24 Mar 2023 09:43:53 -0700
Beau Belgrave <[email protected]> wrote:

> > It was actually merged in 5.8. So sysctl should be sufficient with that.
> > But maybe it's weird to start adding sysctls, when the rest of tracing
> > tunables is AFAIK under /sys/kernel/tracing/ ?
> >
>
> During the TraceFS meetings Steven runs I was asked to add a boot
> parameter and sysctl for user_events to limit the max.
>
> To me, it seems when user_events moves toward namespace awareness
> sysctl might be easier to use from within a namespace to turn knobs.
>
> Happy to change to whatever, but I want to see Steven and Masami agree
> on the approach before doing so.
>
> Steven, do you agree with Masami to move to just sysctl?

We do have some tracing related sysctls already:

# cd /proc/sys/kernel
# ls *trace*
ftrace_dump_on_oops oops_all_cpu_backtrace traceoff_on_warning
ftrace_enabled stack_tracer_enabled tracepoint_printk

Although I would love to deprecated ftrace_enable as that now has a
control in tracefs, but it's not unprecedented to have tracing tunables as
sysctl.

And if we get cmdline boot parameters for free from sysctls then all the
better.

-- Steve

2023-03-26 15:40:57

by Masami Hiramatsu

[permalink] [raw]

Subject: Re: [PATCH v8 11/11] tracing/user_events: Limit global user_event count

On Fri, 24 Mar 2023 13:06:59 -0400
Steven Rostedt <[email protected]> wrote:

> On Fri, 24 Mar 2023 09:43:53 -0700
> Beau Belgrave <[email protected]> wrote:
>
> > > It was actually merged in 5.8. So sysctl should be sufficient with that.
> > > But maybe it's weird to start adding sysctls, when the rest of tracing
> > > tunables is AFAIK under /sys/kernel/tracing/ ?
> > >
> >
> > During the TraceFS meetings Steven runs I was asked to add a boot
> > parameter and sysctl for user_events to limit the max.
> >
> > To me, it seems when user_events moves toward namespace awareness
> > sysctl might be easier to use from within a namespace to turn knobs.
> >
> > Happy to change to whatever, but I want to see Steven and Masami agree
> > on the approach before doing so.
> >
> > Steven, do you agree with Masami to move to just sysctl?
>
> We do have some tracing related sysctls already:
>
> # cd /proc/sys/kernel
> # ls *trace*
> ftrace_dump_on_oops oops_all_cpu_backtrace traceoff_on_warning
> ftrace_enabled stack_tracer_enabled tracepoint_printk
>
> Although I would love to deprecated ftrace_enable as that now has a
> control in tracefs, but it's not unprecedented to have tracing tunables as
> sysctl.
>
> And if we get cmdline boot parameters for free from sysctls then all the
> better.

Yeah, I confirmed that sysctl can be set via kernel parameter. So it is OK
for me to add a sysctl.

Thank you,

>
> -- Steve

--
Masami Hiramatsu (Google) <[email protected]>

2023-03-28 21:02:12

by Steven Rostedt

[permalink] [raw]

Subject: Re: [PATCH v8 03/11] tracing/user_events: Use remote writes for event enablement

On Tue, 21 Feb 2023 13:11:35 -0800
Beau Belgrave <[email protected]> wrote:

> include/linux/user_events.h | 53 ++-
> include/uapi/linux/user_events.h | 15 +-
> kernel/trace/Kconfig | 5 +-
> kernel/trace/trace_events_user.c | 586 ++++++++++++++++++++++++-------
> 4 files changed, 517 insertions(+), 142 deletions(-)
>
> diff --git a/include/linux/user_events.h b/include/linux/user_events.h
> index 3d747c45d2fa..0120b3dd5b03 100644
> --- a/include/linux/user_events.h
> +++ b/include/linux/user_events.h
> @@ -9,13 +9,63 @@
> #ifndef _LINUX_USER_EVENTS_H
> #define _LINUX_USER_EVENTS_H
>
> +#include <linux/list.h>
> +#include <linux/refcount.h>
> +#include <linux/mm_types.h>
> +#include <linux/workqueue.h>
> #include <uapi/linux/user_events.h>
>
> #ifdef CONFIG_USER_EVENTS
> struct user_event_mm {
> + struct list_head link;
> + struct list_head enablers;
> + struct mm_struct *mm;
> + struct user_event_mm *next;
> + refcount_t refcnt;
> + refcount_t tasks;
> + struct rcu_work put_rwork;
> };

This is more of a nit, and not something to change unless there's more real
content to change, but please when making structures tab out the field
names:

struct user_event_mm {
struct list_head link;
struct list_head enablers;
struct mm_struct *mm;
struct user_event_mm *next;
refcount_t refcnt;
refcount_t tasks;
struct rcu_work put_rwork;
};

See how much easier it is to read (and know what fields exist).

> -#endif
>

> #endif /* _LINUX_USER_EVENTS_H */
> diff --git a/include/uapi/linux/user_events.h b/include/uapi/linux/user_events.h
> index 03f92366068d..22521bc622db 100644
> --- a/include/uapi/linux/user_events.h
> +++ b/include/uapi/linux/user_events.h
> @@ -27,12 +27,21 @@ struct user_reg {
> /* Input: Size of the user_reg structure being used */
> __u32 size;
>
> + /* Input: Bit in enable address to use */
> + __u8 enable_bit;
> +
> + /* Input: Enable size in bytes at address */
> + __u8 enable_size;
> +
> + /* Input: Flags for future use, set to 0 */
> + __u16 flags;
> +
> + /* Input: Address to update when enabled */
> + __u64 enable_addr;
> +
> /* Input: Pointer to string with event name, description and flags */
> __u64 name_args;
>
> - /* Output: Bitwise index of the event within the status page */
> - __u32 status_bit;
> -
> /* Output: Index of the event to use when writing data */
> __u32 write_index;
> } __attribute__((__packed__));

May want to tab the above too, but as each field is commented, it's not as
big of an issue.

> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> index d7043043f59c..b61a1bfbfc22 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -791,9 +791,10 @@ config USER_EVENTS
> can be used like an existing kernel trace event. User trace
> events are generated by writing to a tracefs file. User
> processes can determine if their tracing events should be
> - generated by memory mapping a tracefs file and checking for
> - an associated byte being non-zero.
> + generated by registering a value and bit with the kernel
> + that reflects when it is enabled or not.
>
> + See Documentation/trace/user_events.rst.
> If in doubt, say N.
>
> config HIST_TRIGGERS
> diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
> index 070551480747..553a82ee7aeb 100644
> --- a/kernel/trace/trace_events_user.c
> +++ b/kernel/trace/trace_events_user.c
> @@ -19,6 +19,7 @@
> #include <linux/tracefs.h>
> #include <linux/types.h>
> #include <linux/uaccess.h>
> +#include <linux/highmem.h>
> #include <linux/user_events.h>
> #include "trace.h"
> #include "trace_dynevent.h"
> @@ -29,34 +30,11 @@
> #define FIELD_DEPTH_NAME 1
> #define FIELD_DEPTH_SIZE 2
>
> -/*
> - * Limits how many trace_event calls user processes can create:
> - * Must be a power of two of PAGE_SIZE.
> - */
> -#define MAX_PAGE_ORDER 0
> -#define MAX_PAGES (1 << MAX_PAGE_ORDER)
> -#define MAX_BYTES (MAX_PAGES * PAGE_SIZE)
> -#define MAX_EVENTS (MAX_BYTES * 8)
> -
> /* Limit how long of an event name plus args within the subsystem. */
> #define MAX_EVENT_DESC 512
> #define EVENT_NAME(user_event) ((user_event)->tracepoint.name)
> #define MAX_FIELD_ARRAY_SIZE 1024
>
> -/*
> - * The MAP_STATUS_* macros are used for taking a index and determining the
> - * appropriate byte and the bit in the byte to set/reset for an event.
> - *
> - * The lower 3 bits of the index decide which bit to set.
> - * The remaining upper bits of the index decide which byte to use for the bit.
> - *
> - * This is used when an event has a probe attached/removed to reflect live
> - * status of the event wanting tracing or not to user-programs via shared
> - * memory maps.
> - */
> -#define MAP_STATUS_BYTE(index) ((index) >> 3)
> -#define MAP_STATUS_MASK(index) BIT((index) & 7)
> -
> /*
> * Internal bits (kernel side only) to keep track of connected probes:
> * These are used when status is requested in text form about an event. These
> @@ -70,20 +48,14 @@
> #define EVENT_STATUS_OTHER BIT(7)
>
> /*
> - * Stores the pages, tables, and locks for a group of events.
> - * Each logical grouping of events has its own group, with a
> - * matching page for status checks within user programs. This
> - * allows for isolation of events to user programs by various
> - * means.
> + * Stores the system name, tables, and locks for a group of events. This
> + * allows isolation for events by various means.
> */
> struct user_event_group {
> - struct page *pages;
> - char *register_page_data;
> char *system_name;
> struct hlist_node node;
> struct mutex reg_mutex;
> DECLARE_HASHTABLE(register_table, 8);
> - DECLARE_BITMAP(page_bitmap, MAX_EVENTS);
> };
>
> /* Group for init_user_ns mapping, top-most group */
> @@ -106,12 +78,34 @@ struct user_event {
> struct list_head fields;
> struct list_head validators;
> refcount_t refcnt;
> - int index;
> - int flags;
> int min_size;
> char status;
> };

But these should be tabbed out.

>
> +/*
> + * Stores per-mm/event properties that enable an address to be
> + * updated properly for each task. As tasks are forked, we use
> + * these to track enablement sites that are tied to an event.
> + */
> +struct user_event_enabler {
> + struct list_head link;
> + struct user_event *event;
> + unsigned long addr;
> +
> + /* Track enable bit, flags, etc. Aligned for bitops. */
> + unsigned int values;
> +};
> +

And the above.

> +/* Bits 0-5 are for the bit to update upon enable/disable (0-63 allowed) */
> +#define ENABLE_VAL_BIT_MASK 0x3F
> +

This is something that can be added later as a clean up, but if there's a
real issue found with these patches, then make the next version have the
updates.

If you do another version, update the tabs of existing structures in a
separate patch from any content change.

-- Steve

2023-03-28 21:35:44

by Steven Rostedt

[permalink] [raw]

Subject: Re: [PATCH v8 04/11] tracing/user_events: Fixup enable faults asyncly

On Tue, 21 Feb 2023 13:11:36 -0800
Beau Belgrave <[email protected]> wrote:

> @@ -263,7 +277,85 @@ static int user_event_mm_fault_in(struct user_event_mm *mm, unsigned long uaddr)
> }
>
> static int user_event_enabler_write(struct user_event_mm *mm,
> - struct user_event_enabler *enabler)
> + struct user_event_enabler *enabler,
> + bool fixup_fault);
> +
> +static void user_event_enabler_fault_fixup(struct work_struct *work)
> +{
> + struct user_event_enabler_fault *fault = container_of(
> + work, struct user_event_enabler_fault, work);
> + struct user_event_enabler *enabler = fault->enabler;
> + struct user_event_mm *mm = fault->mm;
> + unsigned long uaddr = enabler->addr;
> + int ret;
> +
> + ret = user_event_mm_fault_in(mm, uaddr);
> +
> + if (ret && ret != -ENOENT) {
> + struct user_event *user = enabler->event;
> +
> + pr_warn("user_events: Fault for mm: 0x%pK @ 0x%llx event: %s\n",
> + mm->mm, (unsigned long long)uaddr, EVENT_NAME(user));
> + }
> +
> + /* Prevent state changes from racing */
> + mutex_lock(&event_mutex);
> +
> + /*
> + * If we managed to get the page, re-issue the write. We do not
> + * want to get into a possible infinite loop, which is why we only
> + * attempt again directly if the page came in. If we couldn't get
> + * the page here, then we will try again the next time the event is
> + * enabled/disabled.
> + */

What case would we not get the page? A bad page mapping? User space doing
something silly?

Or something else, for which how can it go into an infinite loop? Can that
only happen if userspace is doing something mischievous?

-- Steve

> + clear_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler));
> +
> + if (!ret) {
> + mmap_read_lock(mm->mm);
> + user_event_enabler_write(mm, enabler, true);
> + mmap_read_unlock(mm->mm);
> + }
> +
> + mutex_unlock(&event_mutex);
> +
> + /* In all cases we no longer need the mm or fault */
> + user_event_mm_put(mm);
> + kmem_cache_free(fault_cache, fault);
> +}
> +
> +static bool user_event_enabler_queue_fault(struct user_event_mm *mm,
> + struct user_event_enabler *enabler)
> +{
> + struct user_event_enabler_fault *fault;
> +
> + fault = kmem_cache_zalloc(fault_cache, GFP_NOWAIT | __GFP_NOWARN);
> +
> + if (!fault)
> + return false;
> +
> + INIT_WORK(&fault->work, user_event_enabler_fault_fixup);
> + fault->mm = user_event_mm_get(mm);
> + fault->enabler = enabler;
> +
> + /* Don't try to queue in again while we have a pending fault */
> + set_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler));
> +
> + if (!schedule_work(&fault->work)) {
> + /* Allow another attempt later */
> + clear_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler));
> +
> + user_event_mm_put(mm);
> + kmem_cache_free(fault_cache, fault);
> +
> + return false;
> + }
> +
> + return true;
> +}
> +

2023-03-28 21:46:47

by Beau Belgrave

[permalink] [raw]

Subject: Re: [PATCH v8 04/11] tracing/user_events: Fixup enable faults asyncly

On Tue, Mar 28, 2023 at 05:20:49PM -0400, Steven Rostedt wrote:
> On Tue, 21 Feb 2023 13:11:36 -0800
> Beau Belgrave <[email protected]> wrote:
>
> > @@ -263,7 +277,85 @@ static int user_event_mm_fault_in(struct user_event_mm *mm, unsigned long uaddr)
> > }
> >
> > static int user_event_enabler_write(struct user_event_mm *mm,
> > - struct user_event_enabler *enabler)
> > + struct user_event_enabler *enabler,
> > + bool fixup_fault);
> > +
> > +static void user_event_enabler_fault_fixup(struct work_struct *work)
> > +{
> > + struct user_event_enabler_fault *fault = container_of(
> > + work, struct user_event_enabler_fault, work);
> > + struct user_event_enabler *enabler = fault->enabler;
> > + struct user_event_mm *mm = fault->mm;
> > + unsigned long uaddr = enabler->addr;
> > + int ret;
> > +
> > + ret = user_event_mm_fault_in(mm, uaddr);
> > +
> > + if (ret && ret != -ENOENT) {
> > + struct user_event *user = enabler->event;
> > +
> > + pr_warn("user_events: Fault for mm: 0x%pK @ 0x%llx event: %s\n",
> > + mm->mm, (unsigned long long)uaddr, EVENT_NAME(user));
> > + }
> > +
> > + /* Prevent state changes from racing */
> > + mutex_lock(&event_mutex);
> > +
> > + /*
> > + * If we managed to get the page, re-issue the write. We do not
> > + * want to get into a possible infinite loop, which is why we only
> > + * attempt again directly if the page came in. If we couldn't get
> > + * the page here, then we will try again the next time the event is
> > + * enabled/disabled.
> > + */
>
> What case would we not get the page? A bad page mapping? User space doing
> something silly?
>

A user space program unmapping the page is the most common I can think
of. A silly action would be unmapping the page while forgetting to call
the unregister IOCTL. We would then possibly see this if the event was
enabled in perf/ftrace before the process exited (and the mm getting
cleaned up).

> Or something else, for which how can it go into an infinite loop? Can that
> only happen if userspace is doing something mischievous?
>

I'm not sure if changing page permissions on the user side would prevent
write permitted mapping in the kernel, but I wanted to ensure if that
type of thing did occur, we wouldn't loop forever. The code lets the mm
decide if a page is ever coming in via fixup_user_fault() with
FAULT_FLAG_WRITE | FAULT_FLAG_REMOTE set.

My understanding is that fixup_user_fault() will retry to get the page
up until it's decided it's either capable of coming in or not. It will
do this since we pass the unlocked bool as a parameter. I used
fixup_user_fault() since it was created for the futex code to handle
this scenario better.

From what I gather, the fault in should only fail for these reasons:
#define VM_FAULT_ERROR (VM_FAULT_OOM | VM_FAULT_SIGBUS | \
VM_FAULT_SIGSEGV | VM_FAULT_HWPOISON | \
VM_FAULT_HWPOISON_LARGE | VM_FAULT_FALLBACK)

If these are hit, I don't believe we want to retry as they aren't likely
to ever get corrected.

Thanks,
-Beau

> -- Steve
>
>
> > + clear_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler));
> > +
> > + if (!ret) {
> > + mmap_read_lock(mm->mm);
> > + user_event_enabler_write(mm, enabler, true);
> > + mmap_read_unlock(mm->mm);
> > + }
> > +
> > + mutex_unlock(&event_mutex);
> > +
> > + /* In all cases we no longer need the mm or fault */
> > + user_event_mm_put(mm);
> > + kmem_cache_free(fault_cache, fault);
> > +}
> > +
> > +static bool user_event_enabler_queue_fault(struct user_event_mm *mm,
> > + struct user_event_enabler *enabler)
> > +{
> > + struct user_event_enabler_fault *fault;
> > +
> > + fault = kmem_cache_zalloc(fault_cache, GFP_NOWAIT | __GFP_NOWARN);
> > +
> > + if (!fault)
> > + return false;
> > +
> > + INIT_WORK(&fault->work, user_event_enabler_fault_fixup);
> > + fault->mm = user_event_mm_get(mm);
> > + fault->enabler = enabler;
> > +
> > + /* Don't try to queue in again while we have a pending fault */
> > + set_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler));
> > +
> > + if (!schedule_work(&fault->work)) {
> > + /* Allow another attempt later */
> > + clear_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler));
> > +
> > + user_event_mm_put(mm);
> > + kmem_cache_free(fault_cache, fault);
> > +
> > + return false;
> > + }
> > +
> > + return true;
> > +}
> > +