Changes v3 => v4:
1. Fix build errors for different config. (kernel test robot)
Changes v2 => v3:
1. Major rewrite after discussions with Steven Rostedt. [1]
2. Remove SHARE_IPMODIFY flag from ftrace code. Instead use the callback
function to communicate this information. (Steven)
3. Add cleanup_direct_functions_after_ipmodify() to clear SHARE_IPMODIFY
on the DIRECT ops when the IPMODIFY ops is removed.
Changes v1 => v2:
1. Fix build errors for different config. (kernel test robot)
Kernel Live Patch (livepatch, or klp) and bpf trampoline are important
features for modern systems. This set allows the two to work on the same
kernel function as the same time.
live patch uses ftrace with IPMODIFY, while bpf trampoline use direct
ftrace. Existing policy does not allow the two to attach to the same kernel
function. This is changed by fine tuning ftrace IPMODIFY policy, and allows
one IPMODIFY ftrace_ops and one DIRECT ftrace_ops on the same kernel
function at the same time. Please see patch 2 and 4 for more details.
Note that, one of the constraint here is to let bpf trampoline use direct
call when it is not working on the same function as live patch. This is
achieved by allowing ftrace code to ask bpf trampoline to make changes.
[1] https://lore.kernel.org/all/[email protected]/
Jiri Olsa (1):
bpf, x64: Allow to use caller address from stack
Song Liu (3):
ftrace: add modify_ftrace_direct_multi_nolock
ftrace: allow IPMODIFY and DIRECT ops on the same function
bpf: support bpf_trampoline on functions with IPMODIFY (e.g.
livepatch)
arch/x86/net/bpf_jit_comp.c | 13 +-
include/linux/bpf.h | 13 ++
include/linux/ftrace.h | 43 +++++
kernel/bpf/trampoline.c | 158 +++++++++++++++++--
kernel/trace/ftrace.c | 306 +++++++++++++++++++++++++++++++-----
5 files changed, 473 insertions(+), 60 deletions(-)
--
2.30.2
IPMODIFY (livepatch) and DIRECT (bpf trampoline) ops are both important
users of ftrace. It is necessary to allow them work on the same function
at the same time.
First, DIRECT ops no longer specify IPMODIFY flag. Instead, DIRECT flag is
handled together with IPMODIFY flag in __ftrace_hash_update_ipmodify().
The, a callback function, ops_func, is added to ftrace_ops. This is used
by ftrace core code to understand whether the DIRECT ops can share with an
IPMODIFY ops. To share with IPMODIFY ops, the DIRECT ops need to implement
the callback function and adjust the direct trampoline accordingly.
If DIRECT ops is attached before the IPMODIFY ops, ftrace core code calls
ENABLE_SHARE_IPMODIFY_PEER on the DIRECT ops before registering the
IPMODIFY ops.
If IPMODIFY ops is attached before the DIRECT ops, ftrace core code calls
ENABLE_SHARE_IPMODIFY_SELF in __ftrace_hash_update_ipmodify. Owner of the
DIRECT ops may return 0 if the DIRECT trampoline can share with IPMODIFY,
so error code otherwise. The error code is propagated to
register_ftrace_direct_multi so that onwer of the DIRECT trampoline can
handle it properly.
For more details, please refer to comment before enum ftrace_ops_cmd.
Link: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Song Liu <[email protected]>
---
include/linux/ftrace.h | 38 +++++++
kernel/trace/ftrace.c | 221 ++++++++++++++++++++++++++++++++++++++---
2 files changed, 243 insertions(+), 16 deletions(-)
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index acb35243ce5d..306bf08acda6 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -208,6 +208,43 @@ enum {
FTRACE_OPS_FL_DIRECT = BIT(17),
};
+/*
+ * FTRACE_OPS_CMD_* commands allow the ftrace core logic to request changes
+ * to a ftrace_ops. Note, the requests may fail.
+ *
+ * ENABLE_SHARE_IPMODIFY_SELF - enable a DIRECT ops to work on the same
+ * function as an ops with IPMODIFY. Called
+ * when the DIRECT ops is being registered.
+ * This is called with both direct_mutex and
+ * ftrace_lock are locked.
+ *
+ * ENABLE_SHARE_IPMODIFY_PEER - enable a DIRECT ops to work on the same
+ * function as an ops with IPMODIFY. Called
+ * when the other ops (the one with IPMODIFY)
+ * is being registered.
+ * This is called with direct_mutex locked.
+ *
+ * DISABLE_SHARE_IPMODIFY_PEER - disable a DIRECT ops to work on the same
+ * function as an ops with IPMODIFY. Called
+ * when the other ops (the one with IPMODIFY)
+ * is being unregistered.
+ * This is called with direct_mutex locked.
+ */
+enum ftrace_ops_cmd {
+ FTRACE_OPS_CMD_ENABLE_SHARE_IPMODIFY_SELF,
+ FTRACE_OPS_CMD_ENABLE_SHARE_IPMODIFY_PEER,
+ FTRACE_OPS_CMD_DISABLE_SHARE_IPMODIFY_PEER,
+};
+
+/*
+ * For most ftrace_ops_cmd,
+ * Returns:
+ * 0 - Success.
+ * -EBUSY - The operation cannot process
+ * -EAGAIN - The operation cannot process tempoorarily.
+ */
+typedef int (*ftrace_ops_func_t)(struct ftrace_ops *op, enum ftrace_ops_cmd cmd);
+
#ifdef CONFIG_DYNAMIC_FTRACE
/* The hash used to know what functions callbacks trace */
struct ftrace_ops_hash {
@@ -250,6 +287,7 @@ struct ftrace_ops {
unsigned long trampoline;
unsigned long trampoline_size;
struct list_head list;
+ ftrace_ops_func_t ops_func;
#endif
};
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 0c15ec997c13..f52efbd13e51 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1861,6 +1861,8 @@ static void ftrace_hash_rec_enable_modify(struct ftrace_ops *ops,
ftrace_hash_rec_update_modify(ops, filter_hash, 1);
}
+static bool ops_references_ip(struct ftrace_ops *ops, unsigned long ip);
+
/*
* Try to update IPMODIFY flag on each ftrace_rec. Return 0 if it is OK
* or no-needed to update, -EBUSY if it detects a conflict of the flag
@@ -1869,6 +1871,13 @@ static void ftrace_hash_rec_enable_modify(struct ftrace_ops *ops,
* - If the hash is NULL, it hits all recs (if IPMODIFY is set, this is rejected)
* - If the hash is EMPTY_HASH, it hits nothing
* - Anything else hits the recs which match the hash entries.
+ *
+ * DIRECT ops does not have IPMODIFY flag, but we still need to check it
+ * against functions with FTRACE_FL_IPMODIFY. If there is any overlap, call
+ * ops_func(SHARE_IPMODIFY_SELF) to make sure current ops can share with
+ * IPMODIFY. If ops_func(SHARE_IPMODIFY_SELF) returns non-zero, propagate
+ * the return value to the caller and eventually to the owner of the DIRECT
+ * ops.
*/
static int __ftrace_hash_update_ipmodify(struct ftrace_ops *ops,
struct ftrace_hash *old_hash,
@@ -1877,17 +1886,23 @@ static int __ftrace_hash_update_ipmodify(struct ftrace_ops *ops,
struct ftrace_page *pg;
struct dyn_ftrace *rec, *end = NULL;
int in_old, in_new;
+ bool is_ipmodify, is_direct;
/* Only update if the ops has been registered */
if (!(ops->flags & FTRACE_OPS_FL_ENABLED))
return 0;
- if (!(ops->flags & FTRACE_OPS_FL_IPMODIFY))
+ is_ipmodify = ops->flags & FTRACE_OPS_FL_IPMODIFY;
+ is_direct = ops->flags & FTRACE_OPS_FL_DIRECT;
+
+ /* either IPMODIFY nor DIRECT, skip */
+ if (!is_ipmodify && !is_direct)
return 0;
/*
- * Since the IPMODIFY is a very address sensitive action, we do not
- * allow ftrace_ops to set all functions to new hash.
+ * Since the IPMODIFY and DIRECT are very address sensitive
+ * actions, we do not allow ftrace_ops to set all functions to new
+ * hash.
*/
if (!new_hash || !old_hash)
return -EINVAL;
@@ -1905,12 +1920,30 @@ static int __ftrace_hash_update_ipmodify(struct ftrace_ops *ops,
continue;
if (in_new) {
- /* New entries must ensure no others are using it */
- if (rec->flags & FTRACE_FL_IPMODIFY)
- goto rollback;
- rec->flags |= FTRACE_FL_IPMODIFY;
- } else /* Removed entry */
+ if (rec->flags & FTRACE_FL_IPMODIFY) {
+ int ret;
+
+ /* Cannot have two ipmodify on same rec */
+ if (is_ipmodify)
+ goto rollback;
+
+ /*
+ * Another ops with IPMODIFY is already
+ * attached. We are now attaching a direct
+ * ops. Run SHARE_IPMODIFY_SELF, to check
+ * whether sharing is supported.
+ */
+ if (!ops->ops_func)
+ return -EBUSY;
+ ret = ops->ops_func(ops, FTRACE_OPS_CMD_ENABLE_SHARE_IPMODIFY_SELF);
+ if (ret)
+ return ret;
+ } else if (is_ipmodify) {
+ rec->flags |= FTRACE_FL_IPMODIFY;
+ }
+ } else if (is_ipmodify) {
rec->flags &= ~FTRACE_FL_IPMODIFY;
+ }
} while_for_each_ftrace_rec();
return 0;
@@ -2455,7 +2488,7 @@ static void call_direct_funcs(unsigned long ip, unsigned long pip,
struct ftrace_ops direct_ops = {
.func = call_direct_funcs,
.flags = FTRACE_OPS_FL_IPMODIFY
- | FTRACE_OPS_FL_DIRECT | FTRACE_OPS_FL_SAVE_REGS
+ | FTRACE_OPS_FL_SAVE_REGS
| FTRACE_OPS_FL_PERMANENT,
/*
* By declaring the main trampoline as this trampoline
@@ -3072,14 +3105,14 @@ static inline int ops_traces_mod(struct ftrace_ops *ops)
}
/*
- * Check if the current ops references the record.
+ * Check if the current ops references the given ip.
*
* If the ops traces all functions, then it was already accounted for.
* If the ops does not trace the current record function, skip it.
* If the ops ignores the function via notrace filter, skip it.
*/
-static inline bool
-ops_references_rec(struct ftrace_ops *ops, struct dyn_ftrace *rec)
+static bool
+ops_references_ip(struct ftrace_ops *ops, unsigned long ip)
{
/* If ops isn't enabled, ignore it */
if (!(ops->flags & FTRACE_OPS_FL_ENABLED))
@@ -3091,16 +3124,29 @@ ops_references_rec(struct ftrace_ops *ops, struct dyn_ftrace *rec)
/* The function must be in the filter */
if (!ftrace_hash_empty(ops->func_hash->filter_hash) &&
- !__ftrace_lookup_ip(ops->func_hash->filter_hash, rec->ip))
+ !__ftrace_lookup_ip(ops->func_hash->filter_hash, ip))
return false;
/* If in notrace hash, we ignore it too */
- if (ftrace_lookup_ip(ops->func_hash->notrace_hash, rec->ip))
+ if (ftrace_lookup_ip(ops->func_hash->notrace_hash, ip))
return false;
return true;
}
+/*
+ * Check if the current ops references the record.
+ *
+ * If the ops traces all functions, then it was already accounted for.
+ * If the ops does not trace the current record function, skip it.
+ * If the ops ignores the function via notrace filter, skip it.
+ */
+static bool
+ops_references_rec(struct ftrace_ops *ops, struct dyn_ftrace *rec)
+{
+ return ops_references_ip(ops, rec->ip);
+}
+
static int ftrace_update_code(struct module *mod, struct ftrace_page *new_pgs)
{
bool init_nop = ftrace_need_init_nop();
@@ -5545,8 +5591,7 @@ int modify_ftrace_direct(unsigned long ip,
}
EXPORT_SYMBOL_GPL(modify_ftrace_direct);
-#define MULTI_FLAGS (FTRACE_OPS_FL_IPMODIFY | FTRACE_OPS_FL_DIRECT | \
- FTRACE_OPS_FL_SAVE_REGS)
+#define MULTI_FLAGS (FTRACE_OPS_FL_DIRECT | FTRACE_OPS_FL_SAVE_REGS)
static int check_direct_multi(struct ftrace_ops *ops)
{
@@ -8004,6 +8049,137 @@ int ftrace_is_dead(void)
return ftrace_disabled;
}
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
+/*
+ * When registering ftrace_ops with IPMODIFY, it is necessary to make sure
+ * it doesn't conflict with any direct ftrace_ops. If there is existing
+ * direct ftrace_ops on a kernel function being patched, call
+ * FTRACE_OPS_CMD_ENABLE_SHARE_IPMODIFY_PEER on it to enable sharing.
+ *
+ * @ops: ftrace_ops being registered.
+ *
+ * Returns:
+ * 0 - @ops does not have IPMODIFY or @ops itself is DIRECT, no
+ * change needed;
+ * 1 - @ops has IPMODIFY, hold direct_mutex;
+ * -EBUSY - currently registered DIRECT ftrace_ops cannot share the
+ * same function with IPMODIFY, abort the register.
+ * -EAGAIN - cannot make changes to currently registered DIRECT
+ * ftrace_ops due to rare race conditions. Should retry
+ * later. This is needed to avoid potential deadlocks
+ * on the DIRECT ftrace_ops side.
+ */
+static int prepare_direct_functions_for_ipmodify(struct ftrace_ops *ops)
+ __acquires(&direct_mutex)
+{
+ struct ftrace_func_entry *entry;
+ struct ftrace_hash *hash;
+ struct ftrace_ops *op;
+ int size, i, ret;
+
+ if (!(ops->flags & FTRACE_OPS_FL_IPMODIFY))
+ return 0;
+
+ mutex_lock(&direct_mutex);
+
+ hash = ops->func_hash->filter_hash;
+ size = 1 << hash->size_bits;
+ for (i = 0; i < size; i++) {
+ hlist_for_each_entry(entry, &hash->buckets[i], hlist) {
+ unsigned long ip = entry->ip;
+ bool found_op = false;
+
+ mutex_lock(&ftrace_lock);
+ do_for_each_ftrace_op(op, ftrace_ops_list) {
+ if (!(op->flags & FTRACE_OPS_FL_DIRECT))
+ continue;
+ if (ops_references_ip(op, ip)) {
+ found_op = true;
+ break;
+ }
+ } while_for_each_ftrace_op(op);
+ mutex_unlock(&ftrace_lock);
+
+ if (found_op) {
+ if (!op->ops_func) {
+ ret = -EBUSY;
+ goto err_out;
+ }
+ ret = op->ops_func(op, FTRACE_OPS_CMD_ENABLE_SHARE_IPMODIFY_PEER);
+ if (ret)
+ goto err_out;
+ }
+ }
+ }
+
+ /*
+ * Didn't find any overlap with direct ftrace_ops, or the direct
+ * function can share with ipmodify. Hold direct_mutex to make sure
+ * this doesn't change until we are done.
+ */
+ return 1;
+
+err_out:
+ mutex_unlock(&direct_mutex);
+ return ret;
+}
+
+/*
+ * Similar to prepare_direct_functions_for_ipmodify, clean up after ops
+ * with IPMODIFY is unregistered. The cleanup is optional for most DIRECT
+ * ops.
+ */
+static void cleanup_direct_functions_after_ipmodify(struct ftrace_ops *ops)
+{
+ struct ftrace_func_entry *entry;
+ struct ftrace_hash *hash;
+ struct ftrace_ops *op;
+ int size, i;
+
+ if (!(ops->flags & FTRACE_OPS_FL_IPMODIFY))
+ return;
+
+ mutex_lock(&direct_mutex);
+
+ hash = ops->func_hash->filter_hash;
+ size = 1 << hash->size_bits;
+ for (i = 0; i < size; i++) {
+ hlist_for_each_entry(entry, &hash->buckets[i], hlist) {
+ unsigned long ip = entry->ip;
+ bool found_op = false;
+
+ mutex_lock(&ftrace_lock);
+ do_for_each_ftrace_op(op, ftrace_ops_list) {
+ if (!(op->flags & FTRACE_OPS_FL_DIRECT))
+ continue;
+ if (ops_references_ip(op, ip)) {
+ found_op = true;
+ break;
+ }
+ } while_for_each_ftrace_op(op);
+ mutex_unlock(&ftrace_lock);
+
+ /* The cleanup is optional, iggore any errors */
+ if (found_op && op->ops_func)
+ op->ops_func(op, FTRACE_OPS_CMD_DISABLE_SHARE_IPMODIFY_PEER);
+ }
+ }
+ mutex_unlock(&direct_mutex);
+}
+
+#else /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
+
+static int prepare_direct_functions_for_ipmodify(struct ftrace_ops *ops)
+{
+ return 0;
+}
+
+static void cleanup_direct_functions_after_ipmodify(struct ftrace_ops *ops)
+{
+}
+
+#endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
+
/**
* register_ftrace_function - register a function for profiling
* @ops: ops structure that holds the function for profiling.
@@ -8016,17 +8192,29 @@ int ftrace_is_dead(void)
* recursive loop.
*/
int register_ftrace_function(struct ftrace_ops *ops)
+ __releases(&direct_mutex)
{
+ bool direct_mutex_locked = false;
int ret;
ftrace_ops_init(ops);
+ ret = prepare_direct_functions_for_ipmodify(ops);
+ if (ret < 0)
+ return ret;
+ else if (ret == 1)
+ direct_mutex_locked = true;
+
mutex_lock(&ftrace_lock);
ret = ftrace_startup(ops, 0);
mutex_unlock(&ftrace_lock);
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
+ if (direct_mutex_locked)
+ mutex_unlock(&direct_mutex);
+#endif
return ret;
}
EXPORT_SYMBOL_GPL(register_ftrace_function);
@@ -8045,6 +8233,7 @@ int unregister_ftrace_function(struct ftrace_ops *ops)
ret = ftrace_shutdown(ops, 0);
mutex_unlock(&ftrace_lock);
+ cleanup_direct_functions_after_ipmodify(ops);
return ret;
}
EXPORT_SYMBOL_GPL(unregister_ftrace_function);
--
2.30.2
When tracing a function with IPMODIFY ftrace_ops (livepatch), the bpf
trampoline must follow the instruction pointer saved on stack. This needs
extra handling for bpf trampolines with BPF_TRAMP_F_CALL_ORIG flag.
Implement bpf_tramp_ftrace_ops_func and use it for the ftrace_ops used
by BPF trampoline. This enables tracing functions with livepatch.
This also requires moving bpf trampoline to *_ftrace_direct_mult APIs.
Link: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Song Liu <[email protected]>
---
include/linux/bpf.h | 8 ++
kernel/bpf/trampoline.c | 158 +++++++++++++++++++++++++++++++++++-----
2 files changed, 149 insertions(+), 17 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 7496842a4671..f35c59e0b742 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -47,6 +47,7 @@ struct kobject;
struct mem_cgroup;
struct module;
struct bpf_func_state;
+struct ftrace_ops;
extern struct idr btf_idr;
extern spinlock_t btf_idr_lock;
@@ -756,6 +757,11 @@ struct btf_func_model {
*/
#define BPF_TRAMP_F_ORIG_STACK BIT(5)
+/* This trampoline is on a function with another ftrace_ops with IPMODIFY,
+ * e.g., a live patch. This flag is set and cleared by ftrace call backs,
+ */
+#define BPF_TRAMP_F_SHARE_IPMODIFY BIT(6)
+
/* Each call __bpf_prog_enter + call bpf_func + call __bpf_prog_exit is ~50
* bytes on x86.
*/
@@ -838,9 +844,11 @@ struct bpf_tramp_image {
struct bpf_trampoline {
/* hlist for trampoline_table */
struct hlist_node hlist;
+ struct ftrace_ops *fops;
/* serializes access to fields of this trampoline */
struct mutex mutex;
refcount_t refcnt;
+ u32 flags;
u64 key;
struct {
struct btf_func_model model;
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index fd69812412ca..fa901aef7930 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -13,6 +13,7 @@
#include <linux/static_call.h>
#include <linux/bpf_verifier.h>
#include <linux/bpf_lsm.h>
+#include <linux/delay.h>
/* dummy _ops. The verifier will operate on target program's ops. */
const struct bpf_verifier_ops bpf_extension_verifier_ops = {
@@ -29,6 +30,81 @@ static struct hlist_head trampoline_table[TRAMPOLINE_TABLE_SIZE];
/* serializes access to trampoline_table */
static DEFINE_MUTEX(trampoline_mutex);
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
+static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mutex);
+
+static int bpf_tramp_ftrace_ops_func(struct ftrace_ops *ops, enum ftrace_ops_cmd cmd)
+{
+ struct bpf_trampoline *tr = ops->private;
+ int ret = 0;
+
+ if (cmd == FTRACE_OPS_CMD_ENABLE_SHARE_IPMODIFY_SELF) {
+ /* This is called inside register_ftrace_direct_multi(), so
+ * tr->mutex is already locked.
+ */
+ WARN_ON_ONCE(!mutex_is_locked(&tr->mutex));
+
+ /* Instead of updating the trampoline here, we propagate
+ * -EAGAIN to register_ftrace_direct_multi(). Then we can
+ * retry register_ftrace_direct_multi() after updating the
+ * trampoline.
+ */
+ if ((tr->flags & BPF_TRAMP_F_CALL_ORIG) &&
+ !(tr->flags & BPF_TRAMP_F_ORIG_STACK)) {
+ if (WARN_ON_ONCE(tr->flags & BPF_TRAMP_F_SHARE_IPMODIFY))
+ return -EBUSY;
+
+ tr->flags |= BPF_TRAMP_F_SHARE_IPMODIFY;
+ return -EAGAIN;
+ }
+
+ return 0;
+ }
+
+ /* The normal locking order is
+ * tr->mutex => direct_mutex (ftrace.c) => ftrace_lock (ftrace.c)
+ *
+ * The following two commands are called from
+ *
+ * prepare_direct_functions_for_ipmodify
+ * cleanup_direct_functions_after_ipmodify
+ *
+ * In both cases, direct_mutex is already locked. Use
+ * mutex_trylock(&tr->mutex) to avoid deadlock in race condition
+ * (something else is making changes to this same trampoline).
+ */
+ if (!mutex_trylock(&tr->mutex)) {
+ /* sleep 1 ms to make sure whatever holding tr->mutex makes
+ * some progress.
+ */
+ msleep(1);
+ return -EAGAIN;
+ }
+
+ switch (cmd) {
+ case FTRACE_OPS_CMD_ENABLE_SHARE_IPMODIFY_PEER:
+ tr->flags |= BPF_TRAMP_F_SHARE_IPMODIFY;
+
+ if ((tr->flags & BPF_TRAMP_F_CALL_ORIG) &&
+ !(tr->flags & BPF_TRAMP_F_ORIG_STACK))
+ ret = bpf_trampoline_update(tr, false /* lock_direct_mutex */);
+ break;
+ case FTRACE_OPS_CMD_DISABLE_SHARE_IPMODIFY_PEER:
+ tr->flags &= ~BPF_TRAMP_F_SHARE_IPMODIFY;
+
+ if (tr->flags & BPF_TRAMP_F_ORIG_STACK)
+ ret = bpf_trampoline_update(tr, false /* lock_direct_mutex */);
+ break;
+ default:
+ ret = -EINVAL;
+ break;
+ };
+
+ mutex_unlock(&tr->mutex);
+ return ret;
+}
+#endif
+
bool bpf_prog_has_trampoline(const struct bpf_prog *prog)
{
enum bpf_attach_type eatype = prog->expected_attach_type;
@@ -89,6 +165,16 @@ static struct bpf_trampoline *bpf_trampoline_lookup(u64 key)
tr = kzalloc(sizeof(*tr), GFP_KERNEL);
if (!tr)
goto out;
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
+ tr->fops = kzalloc(sizeof(struct ftrace_ops), GFP_KERNEL);
+ if (!tr->fops) {
+ kfree(tr);
+ tr = NULL;
+ goto out;
+ }
+ tr->fops->private = tr;
+ tr->fops->ops_func = bpf_tramp_ftrace_ops_func;
+#endif
tr->key = key;
INIT_HLIST_NODE(&tr->hlist);
@@ -128,7 +214,7 @@ static int unregister_fentry(struct bpf_trampoline *tr, void *old_addr)
int ret;
if (tr->func.ftrace_managed)
- ret = unregister_ftrace_direct((long)ip, (long)old_addr);
+ ret = unregister_ftrace_direct_multi(tr->fops, (long)old_addr);
else
ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, NULL);
@@ -137,15 +223,20 @@ static int unregister_fentry(struct bpf_trampoline *tr, void *old_addr)
return ret;
}
-static int modify_fentry(struct bpf_trampoline *tr, void *old_addr, void *new_addr)
+static int modify_fentry(struct bpf_trampoline *tr, void *old_addr, void *new_addr,
+ bool lock_direct_mutex)
{
void *ip = tr->func.addr;
int ret;
- if (tr->func.ftrace_managed)
- ret = modify_ftrace_direct((long)ip, (long)old_addr, (long)new_addr);
- else
+ if (tr->func.ftrace_managed) {
+ if (lock_direct_mutex)
+ ret = modify_ftrace_direct_multi(tr->fops, (long)new_addr);
+ else
+ ret = modify_ftrace_direct_multi_nolock(tr->fops, (long)new_addr);
+ } else {
ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, new_addr);
+ }
return ret;
}
@@ -163,10 +254,12 @@ static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
if (bpf_trampoline_module_get(tr))
return -ENOENT;
- if (tr->func.ftrace_managed)
- ret = register_ftrace_direct((long)ip, (long)new_addr);
- else
+ if (tr->func.ftrace_managed) {
+ ftrace_set_filter_ip(tr->fops, (unsigned long)ip, 0, 0);
+ ret = register_ftrace_direct_multi(tr->fops, (long)new_addr);
+ } else {
ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, NULL, new_addr);
+ }
if (ret)
bpf_trampoline_module_put(tr);
@@ -332,11 +425,11 @@ static struct bpf_tramp_image *bpf_tramp_image_alloc(u64 key, u32 idx)
return ERR_PTR(err);
}
-static int bpf_trampoline_update(struct bpf_trampoline *tr)
+static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mutex)
{
struct bpf_tramp_image *im;
struct bpf_tramp_links *tlinks;
- u32 flags = BPF_TRAMP_F_RESTORE_REGS;
+ u32 orig_flags = tr->flags;
bool ip_arg = false;
int err, total;
@@ -358,18 +451,31 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr)
goto out;
}
+ /* clear all bits except SHARE_IPMODIFY */
+ tr->flags &= BPF_TRAMP_F_SHARE_IPMODIFY;
+
if (tlinks[BPF_TRAMP_FEXIT].nr_links ||
- tlinks[BPF_TRAMP_MODIFY_RETURN].nr_links)
+ tlinks[BPF_TRAMP_MODIFY_RETURN].nr_links) {
/* NOTE: BPF_TRAMP_F_RESTORE_REGS and BPF_TRAMP_F_SKIP_FRAME
* should not be set together.
*/
- flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME;
+ tr->flags |= BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME;
+ } else {
+ tr->flags |= BPF_TRAMP_F_RESTORE_REGS;
+ }
if (ip_arg)
- flags |= BPF_TRAMP_F_IP_ARG;
+ tr->flags |= BPF_TRAMP_F_IP_ARG;
+
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
+again:
+ if ((tr->flags & BPF_TRAMP_F_SHARE_IPMODIFY) &&
+ (tr->flags & BPF_TRAMP_F_CALL_ORIG))
+ tr->flags |= BPF_TRAMP_F_ORIG_STACK;
+#endif
err = arch_prepare_bpf_trampoline(im, im->image, im->image + PAGE_SIZE,
- &tr->func.model, flags, tlinks,
+ &tr->func.model, tr->flags, tlinks,
tr->func.addr);
if (err < 0)
goto out;
@@ -378,17 +484,34 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr)
WARN_ON(!tr->cur_image && tr->selector);
if (tr->cur_image)
/* progs already running at this address */
- err = modify_fentry(tr, tr->cur_image->image, im->image);
+ err = modify_fentry(tr, tr->cur_image->image, im->image, lock_direct_mutex);
else
/* first time registering */
err = register_fentry(tr, im->image);
+
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
+ if (err == -EAGAIN) {
+ /* -EAGAIN from bpf_tramp_ftrace_ops_func. Now
+ * BPF_TRAMP_F_SHARE_IPMODIFY is set, we can generate the
+ * trampoline again, and retry register.
+ */
+ /* reset fops->func and fops->trampoline for re-register */
+ tr->fops->func = NULL;
+ tr->fops->trampoline = 0;
+ goto again;
+ }
+#endif
if (err)
goto out;
+
if (tr->cur_image)
bpf_tramp_image_put(tr->cur_image);
tr->cur_image = im;
tr->selector++;
out:
+ /* If any error happens, restore previous flags */
+ if (err)
+ tr->flags = orig_flags;
kfree(tlinks);
return err;
}
@@ -454,7 +577,7 @@ static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_tr
hlist_add_head(&link->tramp_hlist, &tr->progs_hlist[kind]);
tr->progs_cnt[kind]++;
- err = bpf_trampoline_update(tr);
+ err = bpf_trampoline_update(tr, true /* lock_direct_mutex */);
if (err) {
hlist_del_init(&link->tramp_hlist);
tr->progs_cnt[kind]--;
@@ -487,7 +610,7 @@ static int __bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, struct bpf_
}
hlist_del_init(&link->tramp_hlist);
tr->progs_cnt[kind]--;
- return bpf_trampoline_update(tr);
+ return bpf_trampoline_update(tr, true /* lock_direct_mutex */);
}
/* bpf_trampoline_unlink_prog() should never fail. */
@@ -715,6 +838,7 @@ void bpf_trampoline_put(struct bpf_trampoline *tr)
* multiple rcu callbacks.
*/
hlist_del(&tr->hlist);
+ kfree(tr->fops);
kfree(tr);
out:
mutex_unlock(&trampoline_mutex);
--
2.30.2
From: Jiri Olsa <[email protected]>
Currently we call the original function by using the absolute address
given at the JIT generation. That's not usable when having trampoline
attached to multiple functions, or the target address changes dynamically
(in case of live patch). In such cases we need to take the return address
from the stack.
Adding support to retrieve the original function address from the stack
by adding new BPF_TRAMP_F_ORIG_STACK flag for arch_prepare_bpf_trampoline
function.
Basically we take the return address of the 'fentry' call:
function + 0: call fentry # stores 'function + 5' address on stack
function + 5: ...
The 'function + 5' address will be used as the address for the
original function to call.
Signed-off-by: Jiri Olsa <[email protected]>
Signed-off-by: Song Liu <[email protected]>
---
arch/x86/net/bpf_jit_comp.c | 13 +++++++++----
include/linux/bpf.h | 5 +++++
2 files changed, 14 insertions(+), 4 deletions(-)
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 54c7f46c453f..e1b0c5ed0b7c 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -2119,10 +2119,15 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
if (flags & BPF_TRAMP_F_CALL_ORIG) {
restore_regs(m, &prog, nr_args, regs_off);
- /* call original function */
- if (emit_call(&prog, orig_call, prog)) {
- ret = -EINVAL;
- goto cleanup;
+ if (flags & BPF_TRAMP_F_ORIG_STACK) {
+ emit_ldx(&prog, BPF_DW, BPF_REG_0, BPF_REG_FP, 8);
+ EMIT2(0xff, 0xd0); /* call *rax */
+ } else {
+ /* call original function */
+ if (emit_call(&prog, orig_call, prog)) {
+ ret = -EINVAL;
+ goto cleanup;
+ }
}
/* remember return value in a stack for bpf prog to access */
emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -8);
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index a5bf00649995..7496842a4671 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -751,6 +751,11 @@ struct btf_func_model {
/* Return the return value of fentry prog. Only used by bpf_struct_ops. */
#define BPF_TRAMP_F_RET_FENTRY_RET BIT(4)
+/* Get original function from stack instead of from provided direct address.
+ * Makes sense for trampolines with fexit or fmod_ret programs.
+ */
+#define BPF_TRAMP_F_ORIG_STACK BIT(5)
+
/* Each call __bpf_prog_enter + call bpf_func + call __bpf_prog_exit is ~50
* bytes on x86.
*/
--
2.30.2
Hi Song,
I love your patch! Perhaps something to improve:
[auto build test WARNING on bpf-next/master]
url: https://github.com/intel-lab-lkp/linux/commits/Song-Liu/ftrace-host-klp-and-bpf-trampoline-together/20220718-135652
base: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
config: x86_64-randconfig-a004 (https://download.01.org/0day-ci/archive/20220718/[email protected]/config)
compiler: gcc-11 (Debian 11.3.0-3) 11.3.0
reproduce (this is a W=1 build):
# https://github.com/intel-lab-lkp/linux/commit/9ef1ec8cb818d8ca70887c8c123f2d579384a6c6
git remote add linux-review https://github.com/intel-lab-lkp/linux
git fetch --no-tags linux-review Song-Liu/ftrace-host-klp-and-bpf-trampoline-together/20220718-135652
git checkout 9ef1ec8cb818d8ca70887c8c123f2d579384a6c6
# save the config file
mkdir build_dir && cp config build_dir/.config
make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash kernel/trace/
If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <[email protected]>
All warnings (new ones prefixed by >>):
kernel/trace/ftrace.c: In function 'register_ftrace_function':
>> kernel/trace/ftrace.c:8197:14: warning: variable 'direct_mutex_locked' set but not used [-Wunused-but-set-variable]
8197 | bool direct_mutex_locked = false;
| ^~~~~~~~~~~~~~~~~~~
vim +/direct_mutex_locked +8197 kernel/trace/ftrace.c
8182
8183 /**
8184 * register_ftrace_function - register a function for profiling
8185 * @ops: ops structure that holds the function for profiling.
8186 *
8187 * Register a function to be called by all functions in the
8188 * kernel.
8189 *
8190 * Note: @ops->func and all the functions it calls must be labeled
8191 * with "notrace", otherwise it will go into a
8192 * recursive loop.
8193 */
8194 int register_ftrace_function(struct ftrace_ops *ops)
8195 __releases(&direct_mutex)
8196 {
> 8197 bool direct_mutex_locked = false;
8198 int ret;
8199
8200 ftrace_ops_init(ops);
8201
8202 ret = prepare_direct_functions_for_ipmodify(ops);
8203 if (ret < 0)
8204 return ret;
8205 else if (ret == 1)
8206 direct_mutex_locked = true;
8207
8208 mutex_lock(&ftrace_lock);
8209
8210 ret = ftrace_startup(ops, 0);
8211
8212 mutex_unlock(&ftrace_lock);
8213
--
0-DAY CI Kernel Test Service
https://01.org/lkp
On Mon 2022-07-18 15:42:25, kernel test robot wrote:
> Hi Song,
>
> I love your patch! Perhaps something to improve:
>
> [auto build test WARNING on bpf-next/master]
>
> url: https://github.com/intel-lab-lkp/linux/commits/Song-Liu/ftrace-host-klp-and-bpf-trampoline-together/20220718-135652
> base: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
> config: x86_64-randconfig-a004 (https://download.01.org/0day-ci/archive/20220718/[email protected]/config)
> compiler: gcc-11 (Debian 11.3.0-3) 11.3.0
> reproduce (this is a W=1 build):
> # https://github.com/intel-lab-lkp/linux/commit/9ef1ec8cb818d8ca70887c8c123f2d579384a6c6
> git remote add linux-review https://github.com/intel-lab-lkp/linux
> git fetch --no-tags linux-review Song-Liu/ftrace-host-klp-and-bpf-trampoline-together/20220718-135652
> git checkout 9ef1ec8cb818d8ca70887c8c123f2d579384a6c6
> # save the config file
> mkdir build_dir && cp config build_dir/.config
> make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash kernel/trace/
>
> If you fix the issue, kindly add following tag where applicable
> Reported-by: kernel test robot <[email protected]>
>
> All warnings (new ones prefixed by >>):
>
> kernel/trace/ftrace.c: In function 'register_ftrace_function':
> >> kernel/trace/ftrace.c:8197:14: warning: variable 'direct_mutex_locked' set but not used [-Wunused-but-set-variable]
> 8197 | bool direct_mutex_locked = false;
> | ^~~~~~~~~~~~~~~~~~~
>
>
> vim +/direct_mutex_locked +8197 kernel/trace/ftrace.c
>
> 8182
> 8183 /**
> 8184 * register_ftrace_function - register a function for profiling
> 8185 * @ops: ops structure that holds the function for profiling.
> 8186 *
> 8187 * Register a function to be called by all functions in the
> 8188 * kernel.
> 8189 *
> 8190 * Note: @ops->func and all the functions it calls must be labeled
> 8191 * with "notrace", otherwise it will go into a
> 8192 * recursive loop.
> 8193 */
> 8194 int register_ftrace_function(struct ftrace_ops *ops)
> 8195 __releases(&direct_mutex)
> 8196 {
> > 8197 bool direct_mutex_locked = false;
> 8198 int ret;
> 8199
> 8200 ftrace_ops_init(ops);
> 8201
> 8202 ret = prepare_direct_functions_for_ipmodify(ops);
> 8203 if (ret < 0)
> 8204 return ret;
> 8205 else if (ret == 1)
> 8206 direct_mutex_locked = true;
Honestly, this is another horrible trick. Would it be possible to
call prepare_direct_functions_for_ipmodify() with direct_mutex
already taken?
I mean something like:
mutex_lock(&direct_mutex);
ret = prepare_direct_functions_for_ipmodify(ops);
if (ret)
goto out:
mutex_lock(&ftrace_lock);
ret = ftrace_startup(ops, 0);
mutex_unlock(&ftrace_lock);
out:
mutex_unlock(&direct_mutex);
return ret;
> 8208 mutex_lock(&ftrace_lock);
> 8209
> 8210 ret = ftrace_startup(ops, 0);
> 8211
> 8212 mutex_unlock(&ftrace_lock);
> 8213
Would be possible to handle tr->mutex the same way to avoid
the trylock? I mean to take it in advance before direct_mutex?
Best Regards,
Petr
> On Jul 18, 2022, at 6:19 AM, Petr Mladek <[email protected]> wrote:
>
> On Mon 2022-07-18 15:42:25, kernel test robot wrote:
>> Hi Song,
>>
>> I love your patch! Perhaps something to improve:
>>
>> [auto build test WARNING on bpf-next/master]
>>
>> url: https://github.com/intel-lab-lkp/linux/commits/Song-Liu/ftrace-host-klp-and-bpf-trampoline-together/20220718-135652
>> base: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
>> config: x86_64-randconfig-a004 (https://download.01.org/0day-ci/archive/20220718/[email protected]/config )
>> compiler: gcc-11 (Debian 11.3.0-3) 11.3.0
>> reproduce (this is a W=1 build):
>> # https://github.com/intel-lab-lkp/linux/commit/9ef1ec8cb818d8ca70887c8c123f2d579384a6c6
>> git remote add linux-review https://github.com/intel-lab-lkp/linux
>> git fetch --no-tags linux-review Song-Liu/ftrace-host-klp-and-bpf-trampoline-together/20220718-135652
>> git checkout 9ef1ec8cb818d8ca70887c8c123f2d579384a6c6
>> # save the config file
>> mkdir build_dir && cp config build_dir/.config
>> make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash kernel/trace/
>>
>> If you fix the issue, kindly add following tag where applicable
>> Reported-by: kernel test robot <[email protected]>
>>
>> All warnings (new ones prefixed by >>):
>>
>> kernel/trace/ftrace.c: In function 'register_ftrace_function':
>>>> kernel/trace/ftrace.c:8197:14: warning: variable 'direct_mutex_locked' set but not used [-Wunused-but-set-variable]
>> 8197 | bool direct_mutex_locked = false;
>> | ^~~~~~~~~~~~~~~~~~~
>>
>>
>> vim +/direct_mutex_locked +8197 kernel/trace/ftrace.c
>>
>> 8182
>> 8183 /**
>> 8184 * register_ftrace_function - register a function for profiling
>> 8185 * @ops: ops structure that holds the function for profiling.
>> 8186 *
>> 8187 * Register a function to be called by all functions in the
>> 8188 * kernel.
>> 8189 *
>> 8190 * Note: @ops->func and all the functions it calls must be labeled
>> 8191 * with "notrace", otherwise it will go into a
>> 8192 * recursive loop.
>> 8193 */
>> 8194 int register_ftrace_function(struct ftrace_ops *ops)
>> 8195 __releases(&direct_mutex)
>> 8196 {
>>> 8197 bool direct_mutex_locked = false;
>> 8198 int ret;
>> 8199
>> 8200 ftrace_ops_init(ops);
>> 8201
>> 8202 ret = prepare_direct_functions_for_ipmodify(ops);
>> 8203 if (ret < 0)
>> 8204 return ret;
>> 8205 else if (ret == 1)
>> 8206 direct_mutex_locked = true;
>
> Honestly, this is another horrible trick. Would it be possible to
> call prepare_direct_functions_for_ipmodify() with direct_mutex
> already taken?
>
> I mean something like:
>
> mutex_lock(&direct_mutex);
>
> ret = prepare_direct_functions_for_ipmodify(ops);
> if (ret)
> goto out:
>
> mutex_lock(&ftrace_lock);
> ret = ftrace_startup(ops, 0);
> mutex_unlock(&ftrace_lock);
>
> out:
> mutex_unlock(&direct_mutex);
> return ret;
Yeah, we can actually do something like this. We can also move the
ops->flags & FTRACE_OPS_FL_IPMODIFY check to
register_ftrace_function(), so we only lock direct_mutex when when
it is necessary.
>
>
>> 8208 mutex_lock(&ftrace_lock);
>> 8209
>> 8210 ret = ftrace_startup(ops, 0);
>> 8211
>> 8212 mutex_unlock(&ftrace_lock);
>> 8213
>
> Would be possible to handle tr->mutex the same way to avoid
> the trylock? I mean to take it in advance before direct_mutex?
Unfortunately, we cannot do this. ftrace code cannot look up
bpf trampolines without locking direct_mutex.
Thanks,
Song
On Sun, 17 Jul 2022 22:54:47 -0700
Song Liu <[email protected]> wrote:
Again, make the subject:
ftrace: Allow IPMODIFY and DIRECT ops on the same function
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index acb35243ce5d..306bf08acda6 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -208,6 +208,43 @@ enum {
> FTRACE_OPS_FL_DIRECT = BIT(17),
> };
>
> +/*
> + * FTRACE_OPS_CMD_* commands allow the ftrace core logic to request changes
> + * to a ftrace_ops. Note, the requests may fail.
> + *
> + * ENABLE_SHARE_IPMODIFY_SELF - enable a DIRECT ops to work on the same
> + * function as an ops with IPMODIFY. Called
> + * when the DIRECT ops is being registered.
> + * This is called with both direct_mutex and
> + * ftrace_lock are locked.
> + *
> + * ENABLE_SHARE_IPMODIFY_PEER - enable a DIRECT ops to work on the same
> + * function as an ops with IPMODIFY. Called
> + * when the other ops (the one with IPMODIFY)
> + * is being registered.
> + * This is called with direct_mutex locked.
> + *
> + * DISABLE_SHARE_IPMODIFY_PEER - disable a DIRECT ops to work on the same
> + * function as an ops with IPMODIFY. Called
> + * when the other ops (the one with IPMODIFY)
> + * is being unregistered.
> + * This is called with direct_mutex locked.
> + */
> +enum ftrace_ops_cmd {
> + FTRACE_OPS_CMD_ENABLE_SHARE_IPMODIFY_SELF,
> + FTRACE_OPS_CMD_ENABLE_SHARE_IPMODIFY_PEER,
> + FTRACE_OPS_CMD_DISABLE_SHARE_IPMODIFY_PEER,
> +};
> +
> +/*
> + * For most ftrace_ops_cmd,
> + * Returns:
> + * 0 - Success.
> + * -EBUSY - The operation cannot process
> + * -EAGAIN - The operation cannot process tempoorarily.
Just state:
Returns:
0 - Success
Negative on failure. The return value is dependent
on the callback.
Let's not bind policy of the callback with ftrace.
> + */
> +typedef int (*ftrace_ops_func_t)(struct ftrace_ops *op, enum ftrace_ops_cmd cmd);
> +
> #ifdef CONFIG_DYNAMIC_FTRACE
> /* The hash used to know what functions callbacks trace */
> struct ftrace_ops_hash {
> @@ -250,6 +287,7 @@ struct ftrace_ops {
> unsigned long trampoline;
> unsigned long trampoline_size;
> struct list_head list;
> + ftrace_ops_func_t ops_func;
> #endif
> };
>
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 0c15ec997c13..f52efbd13e51 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -1861,6 +1861,8 @@ static void ftrace_hash_rec_enable_modify(struct ftrace_ops *ops,
> ftrace_hash_rec_update_modify(ops, filter_hash, 1);
> }
>
> +static bool ops_references_ip(struct ftrace_ops *ops, unsigned long ip);
> +
> /*
> * Try to update IPMODIFY flag on each ftrace_rec. Return 0 if it is OK
> * or no-needed to update, -EBUSY if it detects a conflict of the flag
> @@ -1869,6 +1871,13 @@ static void ftrace_hash_rec_enable_modify(struct ftrace_ops *ops,
> * - If the hash is NULL, it hits all recs (if IPMODIFY is set, this is rejected)
> * - If the hash is EMPTY_HASH, it hits nothing
> * - Anything else hits the recs which match the hash entries.
> + *
> + * DIRECT ops does not have IPMODIFY flag, but we still need to check it
> + * against functions with FTRACE_FL_IPMODIFY. If there is any overlap, call
> + * ops_func(SHARE_IPMODIFY_SELF) to make sure current ops can share with
> + * IPMODIFY. If ops_func(SHARE_IPMODIFY_SELF) returns non-zero, propagate
> + * the return value to the caller and eventually to the owner of the DIRECT
> + * ops.
> */
> static int __ftrace_hash_update_ipmodify(struct ftrace_ops *ops,
> struct ftrace_hash *old_hash,
> @@ -1877,17 +1886,23 @@ static int __ftrace_hash_update_ipmodify(struct ftrace_ops *ops,
> struct ftrace_page *pg;
> struct dyn_ftrace *rec, *end = NULL;
> int in_old, in_new;
> + bool is_ipmodify, is_direct;
>
> /* Only update if the ops has been registered */
> if (!(ops->flags & FTRACE_OPS_FL_ENABLED))
> return 0;
>
> - if (!(ops->flags & FTRACE_OPS_FL_IPMODIFY))
> + is_ipmodify = ops->flags & FTRACE_OPS_FL_IPMODIFY;
> + is_direct = ops->flags & FTRACE_OPS_FL_DIRECT;
> +
> + /* either IPMODIFY nor DIRECT, skip */
> + if (!is_ipmodify && !is_direct)
> return 0;
I wonder if we should also add:
if (WARN_ON_ONCE(is_ipmodify && is_direct))
return 0;
As a direct should never have an ipmodify.
>
> /*
> - * Since the IPMODIFY is a very address sensitive action, we do not
> - * allow ftrace_ops to set all functions to new hash.
> + * Since the IPMODIFY and DIRECT are very address sensitive
> + * actions, we do not allow ftrace_ops to set all functions to new
> + * hash.
> */
> if (!new_hash || !old_hash)
> return -EINVAL;
> @@ -1905,12 +1920,30 @@ static int __ftrace_hash_update_ipmodify(struct ftrace_ops *ops,
> continue;
>
> if (in_new) {
> - /* New entries must ensure no others are using it */
> - if (rec->flags & FTRACE_FL_IPMODIFY)
> - goto rollback;
> - rec->flags |= FTRACE_FL_IPMODIFY;
> - } else /* Removed entry */
> + if (rec->flags & FTRACE_FL_IPMODIFY) {
> + int ret;
> +
> + /* Cannot have two ipmodify on same rec */
> + if (is_ipmodify)
> + goto rollback;
> +
I might add a
FTRACE_WARN_ON(rec->flags &
FTRACE_FL_DIRECT);
Just to be safe.
That is, if this is true, we are adding a new direct function to a record
that already has one.
> + /*
> + * Another ops with IPMODIFY is already
> + * attached. We are now attaching a direct
> + * ops. Run SHARE_IPMODIFY_SELF, to check
> + * whether sharing is supported.
> + */
> + if (!ops->ops_func)
> + return -EBUSY;
> + ret = ops->ops_func(ops, FTRACE_OPS_CMD_ENABLE_SHARE_IPMODIFY_SELF);
> + if (ret)
> + return ret;
> + } else if (is_ipmodify) {
> + rec->flags |= FTRACE_FL_IPMODIFY;
> + }
> + } else if (is_ipmodify) {
> rec->flags &= ~FTRACE_FL_IPMODIFY;
> + }
> } while_for_each_ftrace_rec();
>
> return 0;
> @@ -2455,7 +2488,7 @@ static void call_direct_funcs(unsigned long ip, unsigned long pip,
> struct ftrace_ops direct_ops = {
> .func = call_direct_funcs,
> .flags = FTRACE_OPS_FL_IPMODIFY
> - | FTRACE_OPS_FL_DIRECT | FTRACE_OPS_FL_SAVE_REGS
> + | FTRACE_OPS_FL_SAVE_REGS
> | FTRACE_OPS_FL_PERMANENT,
> /*
> * By declaring the main trampoline as this trampoline
> @@ -3072,14 +3105,14 @@ static inline int ops_traces_mod(struct ftrace_ops *ops)
> }
>
> /*
> - * Check if the current ops references the record.
> + * Check if the current ops references the given ip.
> *
> * If the ops traces all functions, then it was already accounted for.
> * If the ops does not trace the current record function, skip it.
> * If the ops ignores the function via notrace filter, skip it.
> */
> -static inline bool
> -ops_references_rec(struct ftrace_ops *ops, struct dyn_ftrace *rec)
> +static bool
> +ops_references_ip(struct ftrace_ops *ops, unsigned long ip)
> {
> /* If ops isn't enabled, ignore it */
> if (!(ops->flags & FTRACE_OPS_FL_ENABLED))
> @@ -3091,16 +3124,29 @@ ops_references_rec(struct ftrace_ops *ops, struct dyn_ftrace *rec)
>
> /* The function must be in the filter */
> if (!ftrace_hash_empty(ops->func_hash->filter_hash) &&
> - !__ftrace_lookup_ip(ops->func_hash->filter_hash, rec->ip))
> + !__ftrace_lookup_ip(ops->func_hash->filter_hash, ip))
> return false;
>
> /* If in notrace hash, we ignore it too */
> - if (ftrace_lookup_ip(ops->func_hash->notrace_hash, rec->ip))
> + if (ftrace_lookup_ip(ops->func_hash->notrace_hash, ip))
> return false;
>
> return true;
> }
>
> +/*
> + * Check if the current ops references the record.
> + *
> + * If the ops traces all functions, then it was already accounted for.
> + * If the ops does not trace the current record function, skip it.
> + * If the ops ignores the function via notrace filter, skip it.
> + */
> +static bool
> +ops_references_rec(struct ftrace_ops *ops, struct dyn_ftrace *rec)
> +{
> + return ops_references_ip(ops, rec->ip);
> +}
> +
> static int ftrace_update_code(struct module *mod, struct ftrace_page *new_pgs)
> {
> bool init_nop = ftrace_need_init_nop();
> @@ -5545,8 +5591,7 @@ int modify_ftrace_direct(unsigned long ip,
> }
> EXPORT_SYMBOL_GPL(modify_ftrace_direct);
>
> -#define MULTI_FLAGS (FTRACE_OPS_FL_IPMODIFY | FTRACE_OPS_FL_DIRECT | \
> - FTRACE_OPS_FL_SAVE_REGS)
> +#define MULTI_FLAGS (FTRACE_OPS_FL_DIRECT | FTRACE_OPS_FL_SAVE_REGS)
>
> static int check_direct_multi(struct ftrace_ops *ops)
> {
> @@ -8004,6 +8049,137 @@ int ftrace_is_dead(void)
> return ftrace_disabled;
> }
>
> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
> +/*
> + * When registering ftrace_ops with IPMODIFY, it is necessary to make sure
> + * it doesn't conflict with any direct ftrace_ops. If there is existing
> + * direct ftrace_ops on a kernel function being patched, call
> + * FTRACE_OPS_CMD_ENABLE_SHARE_IPMODIFY_PEER on it to enable sharing.
> + *
> + * @ops: ftrace_ops being registered.
> + *
> + * Returns:
> + * 0 - @ops does not have IPMODIFY or @ops itself is DIRECT, no
> + * change needed;
> + * 1 - @ops has IPMODIFY, hold direct_mutex;
> + * -EBUSY - currently registered DIRECT ftrace_ops cannot share the
> + * same function with IPMODIFY, abort the register.
> + * -EAGAIN - cannot make changes to currently registered DIRECT
> + * ftrace_ops due to rare race conditions. Should retry
> + * later. This is needed to avoid potential deadlocks
> + * on the DIRECT ftrace_ops side.
Again, these are ops_func() specific and has nothing to do with the logic
in this file. Just state:
* Returns:
* 0 - @ops does not have IPMODIFY or @ops itself is DIRECT, no
* change needed;
* 1 - @ops has IPMODIFY, hold direct_mutex;
* Negative on error.
And if we move the logic that this does not keep hold of the direct_mutex,
we could just let the callback return any non-zero on error.
> + */
> +static int prepare_direct_functions_for_ipmodify(struct ftrace_ops *ops)
> + __acquires(&direct_mutex)
> +{
> + struct ftrace_func_entry *entry;
> + struct ftrace_hash *hash;
> + struct ftrace_ops *op;
> + int size, i, ret;
> +
> + if (!(ops->flags & FTRACE_OPS_FL_IPMODIFY))
> + return 0;
> +
> + mutex_lock(&direct_mutex);
> +
> + hash = ops->func_hash->filter_hash;
> + size = 1 << hash->size_bits;
> + for (i = 0; i < size; i++) {
> + hlist_for_each_entry(entry, &hash->buckets[i], hlist) {
> + unsigned long ip = entry->ip;
> + bool found_op = false;
> +
> + mutex_lock(&ftrace_lock);
> + do_for_each_ftrace_op(op, ftrace_ops_list) {
> + if (!(op->flags & FTRACE_OPS_FL_DIRECT))
> + continue;
> + if (ops_references_ip(op, ip)) {
> + found_op = true;
> + break;
I think you want a goto here. The macros "do_for_each_ftrace_op() { .. }
while_for_each_ftrace_op()" is a double loop. The break just moves to the
next set of pages and does not break out of the outer loop.
goto out_loop;
> + }
> + } while_for_each_ftrace_op(op);
out_loop:
> + mutex_unlock(&ftrace_lock);
> +
> + if (found_op) {
> + if (!op->ops_func) {
> + ret = -EBUSY;
> + goto err_out;
> + }
> + ret = op->ops_func(op, FTRACE_OPS_CMD_ENABLE_SHARE_IPMODIFY_PEER);
> + if (ret)
> + goto err_out;
> + }
> + }
> + }
> +
> + /*
> + * Didn't find any overlap with direct ftrace_ops, or the direct
> + * function can share with ipmodify. Hold direct_mutex to make sure
> + * this doesn't change until we are done.
> + */
> + return 1;
> +
> +err_out:
> + mutex_unlock(&direct_mutex);
> + return ret;
> +}
> +
> +/*
> + * Similar to prepare_direct_functions_for_ipmodify, clean up after ops
> + * with IPMODIFY is unregistered. The cleanup is optional for most DIRECT
> + * ops.
> + */
> +static void cleanup_direct_functions_after_ipmodify(struct ftrace_ops *ops)
> +{
> + struct ftrace_func_entry *entry;
> + struct ftrace_hash *hash;
> + struct ftrace_ops *op;
> + int size, i;
> +
> + if (!(ops->flags & FTRACE_OPS_FL_IPMODIFY))
> + return;
> +
> + mutex_lock(&direct_mutex);
> +
> + hash = ops->func_hash->filter_hash;
> + size = 1 << hash->size_bits;
> + for (i = 0; i < size; i++) {
> + hlist_for_each_entry(entry, &hash->buckets[i], hlist) {
> + unsigned long ip = entry->ip;
> + bool found_op = false;
> +
> + mutex_lock(&ftrace_lock);
> + do_for_each_ftrace_op(op, ftrace_ops_list) {
> + if (!(op->flags & FTRACE_OPS_FL_DIRECT))
> + continue;
> + if (ops_references_ip(op, ip)) {
> + found_op = true;
> + break;
goto out_loop;
> + }
> + } while_for_each_ftrace_op(op);
out_loop:
> + mutex_unlock(&ftrace_lock);
> +
> + /* The cleanup is optional, iggore any errors */
"ignore"
> + if (found_op && op->ops_func)
> + op->ops_func(op, FTRACE_OPS_CMD_DISABLE_SHARE_IPMODIFY_PEER);
> + }
> + }
> + mutex_unlock(&direct_mutex);
> +}
> +
> +#else /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
> +
> +static int prepare_direct_functions_for_ipmodify(struct ftrace_ops *ops)
> +{
> + return 0;
> +}
> +
> +static void cleanup_direct_functions_after_ipmodify(struct ftrace_ops *ops)
> +{
> +}
> +
> +#endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
> +
> /**
> * register_ftrace_function - register a function for profiling
> * @ops: ops structure that holds the function for profiling.
> @@ -8016,17 +8192,29 @@ int ftrace_is_dead(void)
> * recursive loop.
> */
> int register_ftrace_function(struct ftrace_ops *ops)
> + __releases(&direct_mutex)
> {
> + bool direct_mutex_locked = false;
> int ret;
>
> ftrace_ops_init(ops);
>
I agree with Petr.
Just grab the direct_mutex_lock here.
mutex_lock(&direct_mutex);
> + ret = prepare_direct_functions_for_ipmodify(ops);
> + if (ret < 0)
> + return ret;
goto out_unlock;
> + else if (ret == 1)
> + direct_mutex_locked = true;
> +
Nuke the above;
> mutex_lock(&ftrace_lock);
>
> ret = ftrace_startup(ops, 0);
>
> mutex_unlock(&ftrace_lock);
>
> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
> + if (direct_mutex_locked)
> + mutex_unlock(&direct_mutex);
> +#endif
Change this to:
out_unlock:
mutex_unlock(&direct_mutex);
> return ret;
> }
-- Steve
> EXPORT_SYMBOL_GPL(register_ftrace_function);
> @@ -8045,6 +8233,7 @@ int unregister_ftrace_function(struct ftrace_ops *ops)
> ret = ftrace_shutdown(ops, 0);
> mutex_unlock(&ftrace_lock);
>
> + cleanup_direct_functions_after_ipmodify(ops);
> return ret;
> }
> EXPORT_SYMBOL_GPL(unregister_ftrace_function);
On Tue, 19 Jul 2022 14:28:56 -0400
Steven Rostedt <[email protected]> wrote:
> > + /* Cannot have two ipmodify on same rec */
> > + if (is_ipmodify)
> > + goto rollback;
> > +
>
> I might add a
>
> FTRACE_WARN_ON(rec->flags &
> FTRACE_FL_DIRECT);
Bah, my email client line wrapped this. It was suppose to be:
FTRACE_WARN_ON(rec->flags & FTRACE_FL_DIRECT);
Just so you don't think I wanted that initial formatting ;-)
-- Steve
>
> Just to be safe.
>
> That is, if this is true, we are adding a new direct function to a record
> that already has one.
On Mon, 18 Jul 2022 16:59:51 +0000
Song Liu <[email protected]> wrote:
> >> vim +/direct_mutex_locked +8197 kernel/trace/ftrace.c
> >>
> >> 8182
> >> 8183 /**
> >> 8184 * register_ftrace_function - register a function for profiling
> >> 8185 * @ops: ops structure that holds the function for profiling.
> >> 8186 *
> >> 8187 * Register a function to be called by all functions in the
> >> 8188 * kernel.
> >> 8189 *
> >> 8190 * Note: @ops->func and all the functions it calls must be labeled
> >> 8191 * with "notrace", otherwise it will go into a
> >> 8192 * recursive loop.
> >> 8193 */
> >> 8194 int register_ftrace_function(struct ftrace_ops *ops)
> >> 8195 __releases(&direct_mutex)
> >> 8196 {
> >>> 8197 bool direct_mutex_locked = false;
> >> 8198 int ret;
> >> 8199
> >> 8200 ftrace_ops_init(ops);
> >> 8201
> >> 8202 ret = prepare_direct_functions_for_ipmodify(ops);
> >> 8203 if (ret < 0)
> >> 8204 return ret;
> >> 8205 else if (ret == 1)
> >> 8206 direct_mutex_locked = true;
> >
> > Honestly, this is another horrible trick. Would it be possible to
> > call prepare_direct_functions_for_ipmodify() with direct_mutex
> > already taken?
Agreed. I'm not sure why I didn't notice this in the other versions.
Probably was looking too much at the other logic. :-/
> >
> > I mean something like:
> >
> > mutex_lock(&direct_mutex);
> >
> > ret = prepare_direct_functions_for_ipmodify(ops);
> > if (ret)
> > goto out:
> >
> > mutex_lock(&ftrace_lock);
> > ret = ftrace_startup(ops, 0);
> > mutex_unlock(&ftrace_lock);
> >
> > out:
> > mutex_unlock(&direct_mutex);
> > return ret;
>
> Yeah, we can actually do something like this. We can also move the
> ops->flags & FTRACE_OPS_FL_IPMODIFY check to
> register_ftrace_function(), so we only lock direct_mutex when when
> it is necessary.
No need. Just take the direct_mutex, and perhaps add a:
lockdep_assert_held(&direct_mutex);
in the prepare_direct_functions_for_ipmodify().
This is far from a fast path to do any tricks in trying to optimize it.
-- Steve
> On Jul 19, 2022, at 11:32 AM, Steven Rostedt <[email protected]> wrote:
>
> On Mon, 18 Jul 2022 16:59:51 +0000
> Song Liu <[email protected]> wrote:
>
>>>> vim +/direct_mutex_locked +8197 kernel/trace/ftrace.c
>>>>
>>>> 8182
>>>> 8183 /**
>>>> 8184 * register_ftrace_function - register a function for profiling
>>>> 8185 * @ops: ops structure that holds the function for profiling.
>>>> 8186 *
>>>> 8187 * Register a function to be called by all functions in the
>>>> 8188 * kernel.
>>>> 8189 *
>>>> 8190 * Note: @ops->func and all the functions it calls must be labeled
>>>> 8191 * with "notrace", otherwise it will go into a
>>>> 8192 * recursive loop.
>>>> 8193 */
>>>> 8194 int register_ftrace_function(struct ftrace_ops *ops)
>>>> 8195 __releases(&direct_mutex)
>>>> 8196 {
>>>>> 8197 bool direct_mutex_locked = false;
>>>> 8198 int ret;
>>>> 8199
>>>> 8200 ftrace_ops_init(ops);
>>>> 8201
>>>> 8202 ret = prepare_direct_functions_for_ipmodify(ops);
>>>> 8203 if (ret < 0)
>>>> 8204 return ret;
>>>> 8205 else if (ret == 1)
>>>> 8206 direct_mutex_locked = true;
>>>
>>> Honestly, this is another horrible trick. Would it be possible to
>>> call prepare_direct_functions_for_ipmodify() with direct_mutex
>>> already taken?
>
> Agreed. I'm not sure why I didn't notice this in the other versions.
> Probably was looking too much at the other logic. :-/
>
>>>
>>> I mean something like:
>>>
>>> mutex_lock(&direct_mutex);
>>>
>>> ret = prepare_direct_functions_for_ipmodify(ops);
>>> if (ret)
>>> goto out:
>>>
>>> mutex_lock(&ftrace_lock);
>>> ret = ftrace_startup(ops, 0);
>>> mutex_unlock(&ftrace_lock);
>>>
>>> out:
>>> mutex_unlock(&direct_mutex);
>>> return ret;
>>
>> Yeah, we can actually do something like this. We can also move the
>> ops->flags & FTRACE_OPS_FL_IPMODIFY check to
>> register_ftrace_function(), so we only lock direct_mutex when when
>> it is necessary.
>
> No need. Just take the direct_mutex, and perhaps add a:
>
> lockdep_assert_held(&direct_mutex);
>
> in the prepare_direct_functions_for_ipmodify().
>
> This is far from a fast path to do any tricks in trying to optimize it.
Got it. I will fix these and send v5.
Thanks,
Song
> On Jul 19, 2022, at 11:28 AM, Steven Rostedt <[email protected]> wrote:
>
> On Sun, 17 Jul 2022 22:54:47 -0700
> Song Liu <[email protected]> wrote:
>
> Again, make the subject:
>
> ftrace: Allow IPMODIFY and DIRECT ops on the same function
>
Will fix.
> [...]
>> +
>> +/*
>> + * For most ftrace_ops_cmd,
>> + * Returns:
>> + * 0 - Success.
>> + * -EBUSY - The operation cannot process
>> + * -EAGAIN - The operation cannot process tempoorarily.
>
> Just state:
>
> Returns:
> 0 - Success
> Negative on failure. The return value is dependent
> on the callback.
>
> Let's not bind policy of the callback with ftrace.
Will fix.
>
>> + */
>> +typedef int (*ftrace_ops_func_t)(struct ftrace_ops *op, enum ftrace_ops_cmd cmd);
>> +
>> #ifdef CONFIG_DYNAMIC_FTRACE
>> /* The hash used to know what functions callbacks trace */
>>
[...]
>>
>> - if (!(ops->flags & FTRACE_OPS_FL_IPMODIFY))
>> + is_ipmodify = ops->flags & FTRACE_OPS_FL_IPMODIFY;
>> + is_direct = ops->flags & FTRACE_OPS_FL_DIRECT;
>> +
>> + /* either IPMODIFY nor DIRECT, skip */
>> + if (!is_ipmodify && !is_direct)
>> return 0;
>
> I wonder if we should also add:
>
> if (WARN_ON_ONCE(is_ipmodify && is_direct))
> return 0;
>
> As a direct should never have an ipmodify.
Right, I will also remove IPMODIFY from direct_ops:
@ -2487,8 +2490,7 @@ static void call_direct_funcs(unsigned long ip, unsigned long pip,
struct ftrace_ops direct_ops = {
.func = call_direct_funcs,
- .flags = FTRACE_OPS_FL_IPMODIFY
- | FTRACE_OPS_FL_SAVE_REGS
+ .flags = FTRACE_OPS_FL_SAVE_REGS
| FTRACE_OPS_FL_PERMANENT,
/*
* By declaring the main trampoline as this trampoline
>
>>
>> /*
>> - * Since the IPMODIFY is a very address sensitive action, we do not
>> - * allow ftrace_ops to set all functions to new hash.
>> + * Since the IPMODIFY and DIRECT are very address sensitive
>> + * actions, we do not allow ftrace_ops to set all functions to new
>> + * hash.
[...]
>
> Again, these are ops_func() specific and has nothing to do with the logic
> in this file. Just state:
>
> * Returns:
> * 0 - @ops does not have IPMODIFY or @ops itself is DIRECT, no
> * change needed;
> * 1 - @ops has IPMODIFY, hold direct_mutex;
> * Negative on error.
>
> And if we move the logic that this does not keep hold of the direct_mutex,
> we could just let the callback return any non-zero on error.
>
>> + */
>> +static int prepare_direct_functions_for_ipmodify(struct ftrace_ops *ops)
>> + __acquires(&direct_mutex)
>> +{
>> + struct ftrace_func_entry *entry;
>> + struct ftrace_hash *hash;
>> + struct ftrace_ops *op;
>> + int size, i, ret;
>> +
>> + if (!(ops->flags & FTRACE_OPS_FL_IPMODIFY))
>> + return 0;
>> +
>> + mutex_lock(&direct_mutex);
>> +
>> + hash = ops->func_hash->filter_hash;
>> + size = 1 << hash->size_bits;
>> + for (i = 0; i < size; i++) {
>> + hlist_for_each_entry(entry, &hash->buckets[i], hlist) {
>> + unsigned long ip = entry->ip;
>> + bool found_op = false;
>> +
>> + mutex_lock(&ftrace_lock);
>> + do_for_each_ftrace_op(op, ftrace_ops_list) {
>> + if (!(op->flags & FTRACE_OPS_FL_DIRECT))
>> + continue;
>> + if (ops_references_ip(op, ip)) {
>> + found_op = true;
>> + break;
>
> I think you want a goto here. The macros "do_for_each_ftrace_op() { .. }
> while_for_each_ftrace_op()" is a double loop. The break just moves to the
> next set of pages and does not break out of the outer loop.
Hmmm... really? I didn't see it ...
#define do_for_each_ftrace_op(op, list) \
op = rcu_dereference_raw_check(list); \
do
#define while_for_each_ftrace_op(op) \
while (likely(op = rcu_dereference_raw_check((op)->next)) && \
unlikely((op) != &ftrace_list_end))
Did I miss something...?
>
> goto out_loop;
>
>> + }
>> + } while_for_each_ftrace_op(op);
[...]
>
>> mutex_lock(&ftrace_lock);
>>
>> ret = ftrace_startup(ops, 0);
>>
>> mutex_unlock(&ftrace_lock);
>>
>> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
>> + if (direct_mutex_locked)
>> + mutex_unlock(&direct_mutex);
>> +#endif
>
> Change this to:
>
> out_unlock:
> mutex_unlock(&direct_mutex);
>
We still need #ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS, as
direct_mutex is not defined without that config.
Thanks,
Song
[...]
On Tue, 19 Jul 2022 22:57:52 +0000
Song Liu <[email protected]> wrote:
> >> + hash = ops->func_hash->filter_hash;
> >> + size = 1 << hash->size_bits;
> >> + for (i = 0; i < size; i++) {
> >> + hlist_for_each_entry(entry, &hash->buckets[i], hlist) {
> >> + unsigned long ip = entry->ip;
> >> + bool found_op = false;
> >> +
> >> + mutex_lock(&ftrace_lock);
> >> + do_for_each_ftrace_op(op, ftrace_ops_list) {
> >> + if (!(op->flags & FTRACE_OPS_FL_DIRECT))
> >> + continue;
> >> + if (ops_references_ip(op, ip)) {
> >> + found_op = true;
> >> + break;
> >
> > I think you want a goto here. The macros "do_for_each_ftrace_op() { .. }
> > while_for_each_ftrace_op()" is a double loop. The break just moves to the
> > next set of pages and does not break out of the outer loop.
>
> Hmmm... really? I didn't see it ...
>
>
> #define do_for_each_ftrace_op(op, list) \
> op = rcu_dereference_raw_check(list); \
> do
>
> #define while_for_each_ftrace_op(op) \
> while (likely(op = rcu_dereference_raw_check((op)->next)) && \
> unlikely((op) != &ftrace_list_end))
>
> Did I miss something...?
Bah, you're right. I was confusing it with do_for_each_ftrace_rec(), which
*is* a double loop.
Never mind ;-)
>
> >
> > goto out_loop;
> >
> >> + }
> >> + } while_for_each_ftrace_op(op);
>
> [...]
>
> >
> >> mutex_lock(&ftrace_lock);
> >>
> >> ret = ftrace_startup(ops, 0);
> >>
> >> mutex_unlock(&ftrace_lock);
> >>
> >> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
> >> + if (direct_mutex_locked)
> >> + mutex_unlock(&direct_mutex);
> >> +#endif
> >
> > Change this to:
> >
> > out_unlock:
> > mutex_unlock(&direct_mutex);
> >
>
> We still need #ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS, as
> direct_mutex is not defined without that config.
Ah, right. I just meant to get rid of the if statement.
To keep the code clean, perhaps we should have:
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
# define lock_direct_mutex() mutex_lock(&direct_mutex)
# define unlock_direct_mutex() mutex_unlock(&direct_mutex)
#else
# define lock_direct_mutex() do { } while (0)
# define unlock_direct_mutex() do { } while (0)
#endif
And use that here.
-- Steve
> On Jul 19, 2022, at 11:28 AM, Steven Rostedt <[email protected]> wrote:
>
>> /**
>> * register_ftrace_function - register a function for profiling
>> * @ops: ops structure that holds the function for profiling.
>> @@ -8016,17 +8192,29 @@ int ftrace_is_dead(void)
>> * recursive loop.
>> */
>> int register_ftrace_function(struct ftrace_ops *ops)
>> + __releases(&direct_mutex)
>> {
>> + bool direct_mutex_locked = false;
>> int ret;
>>
>> ftrace_ops_init(ops);
>>
>
> I agree with Petr.
>
> Just grab the direct_mutex_lock here.
>
> mutex_lock(&direct_mutex);
Actually, we cannot blindly lock direct_mutex here, as
register_ftrace_direct() already locks it before calling
register_ftrace_function(). We still need the if (IPMODIFY)
check.
Thanks,
Song
>
>> + ret = prepare_direct_functions_for_ipmodify(ops);
>> + if (ret < 0)
>> + return ret;
>
On Tue, 19 Jul 2022 23:24:35 +0000
Song Liu <[email protected]> wrote:
> Actually, we cannot blindly lock direct_mutex here, as
> register_ftrace_direct() already locks it before calling
> register_ftrace_function(). We still need the if (IPMODIFY)
> check.
Let's not play games with this then.
Create a register_ftrace_function_nolock()
and use that for register_ftrace_direct().
Otherwise it's going to be a nightmare to keep track of.
-- Steve