The tracing ring-buffers can be stored on disk or sent to network
without any copy via splice. However the later doesn't allow real time
processing of the traces. A solution is to give userspace direct access
to the ring-buffer pages via a mapping. An application can now become a
consumer of the ring-buffer, in a similar fashion to what trace_pipe
offers.
Support for this new feature can already be found in libtracefs from
version 1.8, when built with EXTRA_CFLAGS=-DFORCE_MMAP_ENABLE.
Vincent
v13 -> v14:
* All cpu_buffer->mapped readers use READ_ONCE (except for swap_cpu)
* on unmap, sync meta-page teardown with the reader_lock instead of
the synchronize_rcu.
* Add a dedicated spinlock for trace_array ->snapshot and ->mapped.
(intends to fix a lockdep issue)
* Add kerneldoc for flags and Reserved fields.
* Add kselftest for snapshot/map mutual exclusion.
v12 -> v13:
* Swap subbufs_{touched,lost} for Reserved fields.
* Add a flag field in the meta-page.
* Fix CONFIG_TRACER_MAX_TRACE.
* Rebase on top of trace/urgent.
* Add a comment for try_unregister_trigger()
v11 -> v12:
* Fix code sample mmap bug.
* Add logging in sample code.
* Reset tracer in selftest.
* Add a refcount for the snapshot users.
* Prevent mapping when there are snapshot users and vice versa.
* Refine the meta-page.
* Fix types in the meta-page.
* Collect Reviewed-by.
v10 -> v11:
* Add Documentation and code sample.
* Add a selftest.
* Move all the update to the meta-page into a single
rb_update_meta_page().
* rb_update_meta_page() is now called from
ring_buffer_map_get_reader() to fix NOBLOCK callers.
* kerneldoc for struct trace_meta_page.
* Add a patch to zero all the ring-buffer allocations.
v9 -> v10:
* Refactor rb_update_meta_page()
* In-loop declaration for foreach_subbuf_page()
* Check for cpu_buffer->mapped overflow
v8 -> v9:
* Fix the unlock path in ring_buffer_map()
* Fix cpu_buffer cast with rb_work_rq->is_cpu_buffer
* Rebase on linux-trace/for-next (3cb3091138ca0921c4569bcf7ffa062519639b6a)
v7 -> v8:
* Drop the subbufs renaming into bpages
* Use subbuf as a name when relevant
v6 -> v7:
* Rebase onto lore.kernel.org/lkml/[email protected]/
* Support for subbufs
* Rename subbufs into bpages
v5 -> v6:
* Rebase on next-20230802.
* (unsigned long) -> (void *) cast for virt_to_page().
* Add a wait for the GET_READER_PAGE ioctl.
* Move writer fields update (overrun/pages_lost/entries/pages_touched)
in the irq_work.
* Rearrange id in struct buffer_page.
* Rearrange the meta-page.
* ring_buffer_meta_page -> trace_buffer_meta_page.
* Add meta_struct_len into the meta-page.
v4 -> v5:
* Trivial rebase onto 6.5-rc3 (previously 6.4-rc3)
v3 -> v4:
* Add to the meta-page:
- pages_lost / pages_read (allow to compute how full is the
ring-buffer)
- read (allow to compute how many entries can be read)
- A reader_page struct.
* Rename ring_buffer_meta_header -> ring_buffer_meta
* Rename ring_buffer_get_reader_page -> ring_buffer_map_get_reader_page
* Properly consume events on ring_buffer_map_get_reader_page() with
rb_advance_reader().
v2 -> v3:
* Remove data page list (for non-consuming read)
** Implies removing order > 0 meta-page
* Add a new meta page field ->read
* Rename ring_buffer_meta_page_header into ring_buffer_meta_header
v1 -> v2:
* Hide data_pages from the userspace struct
* Fix META_PAGE_MAX_PAGES
* Support for order > 0 meta-page
* Add missing page->mapping.
Vincent Donnefort (6):
ring-buffer: Zero ring-buffer sub-buffers
ring-buffer: Introducing ring-buffer mapping functions
tracing: Add snapshot refcount
tracing: Allow user-space mapping of the ring-buffer
Documentation: tracing: Add ring-buffer mapping
ring-buffer/selftest: Add ring-buffer mapping test
Documentation/trace/index.rst | 1 +
Documentation/trace/ring-buffer-map.rst | 104 ++++++
include/linux/ring_buffer.h | 7 +
include/uapi/linux/trace_mmap.h | 48 +++
kernel/trace/ring_buffer.c | 344 +++++++++++++++++-
kernel/trace/trace.c | 221 +++++++++--
kernel/trace/trace.h | 9 +-
kernel/trace/trace_events_trigger.c | 58 ++-
tools/testing/selftests/ring-buffer/Makefile | 8 +
tools/testing/selftests/ring-buffer/config | 2 +
.../testing/selftests/ring-buffer/map_test.c | 273 ++++++++++++++
11 files changed, 1029 insertions(+), 46 deletions(-)
create mode 100644 Documentation/trace/ring-buffer-map.rst
create mode 100644 include/uapi/linux/trace_mmap.h
create mode 100644 tools/testing/selftests/ring-buffer/Makefile
create mode 100644 tools/testing/selftests/ring-buffer/config
create mode 100644 tools/testing/selftests/ring-buffer/map_test.c
base-commit: e2412e51fdea837b50ce31fea8e5dfc885237f3a
--
2.43.0.594.gd9cf4e227d-goog
In preparation for the ring-buffer memory mapping where each subbuf will
be accessible to user-space, zero all the page allocations.
Signed-off-by: Vincent Donnefort <[email protected]>
Reviewed-by: Masami Hiramatsu (Google) <[email protected]>
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index fd4bfe3ecf01..ca796675c0a1 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1472,7 +1472,8 @@ static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
list_add(&bpage->list, pages);
- page = alloc_pages_node(cpu_to_node(cpu_buffer->cpu), mflags,
+ page = alloc_pages_node(cpu_to_node(cpu_buffer->cpu),
+ mflags | __GFP_ZERO,
cpu_buffer->buffer->subbuf_order);
if (!page)
goto free_pages;
@@ -1557,7 +1558,8 @@ rb_allocate_cpu_buffer(struct trace_buffer *buffer, long nr_pages, int cpu)
cpu_buffer->reader_page = bpage;
- page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL, cpu_buffer->buffer->subbuf_order);
+ page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL | __GFP_ZERO,
+ cpu_buffer->buffer->subbuf_order);
if (!page)
goto fail_free_reader;
bpage->page = page_address(page);
@@ -5525,7 +5527,8 @@ ring_buffer_alloc_read_page(struct trace_buffer *buffer, int cpu)
if (bpage->data)
goto out;
- page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL | __GFP_NORETRY,
+ page = alloc_pages_node(cpu_to_node(cpu),
+ GFP_KERNEL | __GFP_NORETRY | __GFP_ZERO,
cpu_buffer->buffer->subbuf_order);
if (!page) {
kfree(bpage);
--
2.43.0.594.gd9cf4e227d-goog
In preparation for allowing the user-space to map a ring-buffer, add
a set of mapping functions:
ring_buffer_{map,unmap}()
ring_buffer_map_fault()
And controls on the ring-buffer:
ring_buffer_map_get_reader() /* swap reader and head */
Mapping the ring-buffer also involves:
A unique ID for each subbuf of the ring-buffer, currently they are
only identified through their in-kernel VA.
A meta-page, where are stored ring-buffer statistics and a
description for the current reader
The linear mapping exposes the meta-page, and each subbuf of the
ring-buffer, ordered following their unique ID, assigned during the
first mapping.
Once mapped, no subbuf can get in or out of the ring-buffer: the buffer
size will remain unmodified and the splice enabling functions will in
reality simply memcpy the data instead of swapping subbufs.
Signed-off-by: Vincent Donnefort <[email protected]>
diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index fa802db216f9..0841ba8bab14 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -6,6 +6,8 @@
#include <linux/seq_file.h>
#include <linux/poll.h>
+#include <uapi/linux/trace_mmap.h>
+
struct trace_buffer;
struct ring_buffer_iter;
@@ -221,4 +223,9 @@ int trace_rb_cpu_prepare(unsigned int cpu, struct hlist_node *node);
#define trace_rb_cpu_prepare NULL
#endif
+int ring_buffer_map(struct trace_buffer *buffer, int cpu);
+int ring_buffer_unmap(struct trace_buffer *buffer, int cpu);
+struct page *ring_buffer_map_fault(struct trace_buffer *buffer, int cpu,
+ unsigned long pgoff);
+int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu);
#endif /* _LINUX_RING_BUFFER_H */
diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mmap.h
new file mode 100644
index 000000000000..182e05a3004a
--- /dev/null
+++ b/include/uapi/linux/trace_mmap.h
@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _TRACE_MMAP_H_
+#define _TRACE_MMAP_H_
+
+#include <linux/types.h>
+
+/**
+ * struct trace_buffer_meta - Ring-buffer Meta-page description
+ * @meta_page_size: Size of this meta-page.
+ * @meta_struct_len: Size of this structure.
+ * @subbuf_size: Size of each sub-buffer.
+ * @nr_subbufs: Number of subbfs in the ring-buffer.
+ * @reader.lost_events: Number of events lost at the time of the reader swap.
+ * @reader.id: subbuf ID of the current reader. From 0 to @nr_subbufs - 1
+ * @reader.read: Number of bytes read on the reader subbuf.
+ * @flags: Placeholder for now, no defined values.
+ * @entries: Number of entries in the ring-buffer.
+ * @overrun: Number of entries lost in the ring-buffer.
+ * @read: Number of entries that have been read.
+ * @Reserved1: Reserved for future use.
+ * @Reserved2: Reserved for future use.
+ */
+struct trace_buffer_meta {
+ __u32 meta_page_size;
+ __u32 meta_struct_len;
+
+ __u32 subbuf_size;
+ __u32 nr_subbufs;
+
+ struct {
+ __u64 lost_events;
+ __u32 id;
+ __u32 read;
+ } reader;
+
+ __u64 flags;
+
+ __u64 entries;
+ __u64 overrun;
+ __u64 read;
+
+ __u64 Reserved1;
+ __u64 Reserved2;
+};
+
+#endif /* _TRACE_MMAP_H_ */
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index ca796675c0a1..dcb4a0bc7ecb 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -338,6 +338,7 @@ struct buffer_page {
local_t entries; /* entries on this page */
unsigned long real_end; /* real end of data */
unsigned order; /* order of the page */
+ u32 id; /* ID for external mapping */
struct buffer_data_page *page; /* Actual data page */
};
@@ -484,6 +485,12 @@ struct ring_buffer_per_cpu {
u64 read_stamp;
/* pages removed since last reset */
unsigned long pages_removed;
+
+ unsigned int mapped;
+ struct mutex mapping_lock;
+ unsigned long *subbuf_ids; /* ID to addr */
+ struct trace_buffer_meta *meta_page;
+
/* ring buffer pages to update, > 0 to add, < 0 to remove */
long nr_pages_to_update;
struct list_head new_pages; /* new pages to add */
@@ -1548,6 +1555,7 @@ rb_allocate_cpu_buffer(struct trace_buffer *buffer, long nr_pages, int cpu)
init_irq_work(&cpu_buffer->irq_work.work, rb_wake_up_waiters);
init_waitqueue_head(&cpu_buffer->irq_work.waiters);
init_waitqueue_head(&cpu_buffer->irq_work.full_waiters);
+ mutex_init(&cpu_buffer->mapping_lock);
bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
GFP_KERNEL, cpu_to_node(cpu));
@@ -1738,8 +1746,6 @@ bool ring_buffer_time_stamp_abs(struct trace_buffer *buffer)
return buffer->time_stamp_abs;
}
-static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
-
static inline unsigned long rb_page_entries(struct buffer_page *bpage)
{
return local_read(&bpage->entries) & RB_WRITE_MASK;
@@ -5160,6 +5166,19 @@ static void rb_clear_buffer_page(struct buffer_page *page)
page->read = 0;
}
+static void rb_update_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
+{
+ struct trace_buffer_meta *meta = cpu_buffer->meta_page;
+
+ WRITE_ONCE(meta->reader.read, cpu_buffer->reader_page->read);
+ WRITE_ONCE(meta->reader.id, cpu_buffer->reader_page->id);
+ WRITE_ONCE(meta->reader.lost_events, cpu_buffer->lost_events);
+
+ WRITE_ONCE(meta->entries, local_read(&cpu_buffer->entries));
+ WRITE_ONCE(meta->overrun, local_read(&cpu_buffer->overrun));
+ WRITE_ONCE(meta->read, cpu_buffer->read);
+}
+
static void
rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
{
@@ -5204,6 +5223,9 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
cpu_buffer->lost_events = 0;
cpu_buffer->last_overrun = 0;
+ if (READ_ONCE(cpu_buffer->mapped))
+ rb_update_meta_page(cpu_buffer);
+
rb_head_page_activate(cpu_buffer);
cpu_buffer->pages_removed = 0;
}
@@ -5418,6 +5440,12 @@ int ring_buffer_swap_cpu(struct trace_buffer *buffer_a,
cpu_buffer_a = buffer_a->buffers[cpu];
cpu_buffer_b = buffer_b->buffers[cpu];
+ /* It's up to the callers to not try to swap mapped buffers */
+ if (WARN_ON_ONCE(cpu_buffer_a->mapped || cpu_buffer_b->mapped)) {
+ ret = -EBUSY;
+ goto out;
+ }
+
/* At least make sure the two buffers are somewhat the same */
if (cpu_buffer_a->nr_pages != cpu_buffer_b->nr_pages)
goto out;
@@ -5682,7 +5710,8 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
* Otherwise, we can simply swap the page with the one passed in.
*/
if (read || (len < (commit - read)) ||
- cpu_buffer->reader_page == cpu_buffer->commit_page) {
+ cpu_buffer->reader_page == cpu_buffer->commit_page ||
+ READ_ONCE(cpu_buffer->mapped)) {
struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
unsigned int rpos = read;
unsigned int pos = 0;
@@ -5901,6 +5930,11 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
cpu_buffer = buffer->buffers[cpu];
+ if (READ_ONCE(cpu_buffer->mapped)) {
+ err = -EBUSY;
+ goto error;
+ }
+
/* Update the number of pages to match the new size */
nr_pages = old_size * buffer->buffers[cpu]->nr_pages;
nr_pages = DIV_ROUND_UP(nr_pages, buffer->subbuf_size);
@@ -6002,6 +6036,301 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
}
EXPORT_SYMBOL_GPL(ring_buffer_subbuf_order_set);
+#define subbuf_page(off, start) \
+ virt_to_page((void *)(start + (off << PAGE_SHIFT)))
+
+#define foreach_subbuf_page(sub_order, start, page) \
+ page = subbuf_page(0, (start)); \
+ for (int __off = 0; __off < (1 << (sub_order)); \
+ __off++, page = subbuf_page(__off, (start)))
+
+static inline void subbuf_map_prepare(unsigned long subbuf_start, int order)
+{
+ struct page *page;
+
+ /*
+ * When allocating order > 0 pages, only the first struct page has a
+ * refcount > 1. Increasing the refcount here ensures none of the struct
+ * page composing the sub-buffer is freeed when the mapping is closed.
+ */
+ foreach_subbuf_page(order, subbuf_start, page)
+ page_ref_inc(page);
+}
+
+static inline void subbuf_unmap(unsigned long subbuf_start, int order)
+{
+ struct page *page;
+
+ foreach_subbuf_page(order, subbuf_start, page) {
+ page_ref_dec(page);
+ page->mapping = NULL;
+ }
+}
+
+static void rb_free_subbuf_ids(struct ring_buffer_per_cpu *cpu_buffer)
+{
+ int sub_id;
+
+ for (sub_id = 0; sub_id < cpu_buffer->nr_pages + 1; sub_id++)
+ subbuf_unmap(cpu_buffer->subbuf_ids[sub_id],
+ cpu_buffer->buffer->subbuf_order);
+
+ kfree(cpu_buffer->subbuf_ids);
+ cpu_buffer->subbuf_ids = NULL;
+}
+
+static int rb_alloc_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
+{
+ if (cpu_buffer->meta_page)
+ return 0;
+
+ cpu_buffer->meta_page = page_to_virt(alloc_page(GFP_USER | __GFP_ZERO));
+ if (!cpu_buffer->meta_page)
+ return -ENOMEM;
+
+ return 0;
+}
+
+static void rb_free_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
+{
+ unsigned long addr = (unsigned long)cpu_buffer->meta_page;
+
+ virt_to_page((void *)addr)->mapping = NULL;
+ free_page(addr);
+ cpu_buffer->meta_page = NULL;
+}
+
+static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer,
+ unsigned long *subbuf_ids)
+{
+ struct trace_buffer_meta *meta = cpu_buffer->meta_page;
+ unsigned int nr_subbufs = cpu_buffer->nr_pages + 1;
+ struct buffer_page *first_subbuf, *subbuf;
+ int id = 0;
+
+ subbuf_ids[id] = (unsigned long)cpu_buffer->reader_page->page;
+ subbuf_map_prepare(subbuf_ids[id], cpu_buffer->buffer->subbuf_order);
+ cpu_buffer->reader_page->id = id++;
+
+ first_subbuf = subbuf = rb_set_head_page(cpu_buffer);
+ do {
+ if (id >= nr_subbufs) {
+ WARN_ON(1);
+ break;
+ }
+
+ subbuf_ids[id] = (unsigned long)subbuf->page;
+ subbuf->id = id;
+ subbuf_map_prepare(subbuf_ids[id], cpu_buffer->buffer->subbuf_order);
+
+ rb_inc_page(&subbuf);
+ id++;
+ } while (subbuf != first_subbuf);
+
+ /* install subbuf ID to kern VA translation */
+ cpu_buffer->subbuf_ids = subbuf_ids;
+
+ meta->meta_page_size = PAGE_SIZE;
+ meta->meta_struct_len = sizeof(*meta);
+ meta->nr_subbufs = nr_subbufs;
+ meta->subbuf_size = cpu_buffer->buffer->subbuf_size + BUF_PAGE_HDR_SIZE;
+
+ rb_update_meta_page(cpu_buffer);
+}
+
+static inline struct ring_buffer_per_cpu *
+rb_get_mapped_buffer(struct trace_buffer *buffer, int cpu)
+{
+ struct ring_buffer_per_cpu *cpu_buffer;
+
+ if (!cpumask_test_cpu(cpu, buffer->cpumask))
+ return ERR_PTR(-EINVAL);
+
+ cpu_buffer = buffer->buffers[cpu];
+
+ mutex_lock(&cpu_buffer->mapping_lock);
+
+ if (!cpu_buffer->mapped) {
+ mutex_unlock(&cpu_buffer->mapping_lock);
+ return ERR_PTR(-ENODEV);
+ }
+
+ return cpu_buffer;
+}
+
+static inline void rb_put_mapped_buffer(struct ring_buffer_per_cpu *cpu_buffer)
+{
+ mutex_unlock(&cpu_buffer->mapping_lock);
+}
+
+int ring_buffer_map(struct trace_buffer *buffer, int cpu)
+{
+ struct ring_buffer_per_cpu *cpu_buffer;
+ unsigned long flags, *subbuf_ids;
+ int err = 0;
+
+ if (!cpumask_test_cpu(cpu, buffer->cpumask))
+ return -EINVAL;
+
+ cpu_buffer = buffer->buffers[cpu];
+
+ mutex_lock(&cpu_buffer->mapping_lock);
+
+ if (cpu_buffer->mapped) {
+ if (cpu_buffer->mapped == UINT_MAX)
+ err = -EBUSY;
+ else
+ WRITE_ONCE(cpu_buffer->mapped, cpu_buffer->mapped + 1);
+ mutex_unlock(&cpu_buffer->mapping_lock);
+ return err;
+ }
+
+ /* prevent another thread from changing buffer/sub-buffer sizes */
+ mutex_lock(&buffer->mutex);
+
+ err = rb_alloc_meta_page(cpu_buffer);
+ if (err)
+ goto unlock;
+
+ /* subbuf_ids include the reader while nr_pages does not */
+ subbuf_ids = kzalloc(sizeof(*subbuf_ids) * (cpu_buffer->nr_pages + 1),
+ GFP_KERNEL);
+ if (!subbuf_ids) {
+ rb_free_meta_page(cpu_buffer);
+ err = -ENOMEM;
+ goto unlock;
+ }
+
+ atomic_inc(&cpu_buffer->resize_disabled);
+
+ /*
+ * Lock all readers to block any subbuf swap until the subbuf IDs are
+ * assigned.
+ */
+ raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+
+ rb_setup_ids_meta_page(cpu_buffer, subbuf_ids);
+ cpu_buffer->mapped = 1;
+
+ raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+unlock:
+ mutex_unlock(&buffer->mutex);
+ mutex_unlock(&cpu_buffer->mapping_lock);
+
+ return err;
+}
+
+int ring_buffer_unmap(struct trace_buffer *buffer, int cpu)
+{
+ struct ring_buffer_per_cpu *cpu_buffer;
+ unsigned long flags;
+ int err = 0;
+
+ if (!cpumask_test_cpu(cpu, buffer->cpumask))
+ return -EINVAL;
+
+ cpu_buffer = buffer->buffers[cpu];
+
+ mutex_lock(&cpu_buffer->mapping_lock);
+
+ if (!cpu_buffer->mapped) {
+ err = -ENODEV;
+ goto out;
+ } else if (cpu_buffer->mapped > 1) {
+ WRITE_ONCE(cpu_buffer->mapped, cpu_buffer->mapped - 1);
+ goto out;
+ }
+
+ mutex_lock(&buffer->mutex);
+ raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+
+ cpu_buffer->mapped = 0;
+
+ raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+
+ rb_free_subbuf_ids(cpu_buffer);
+ rb_free_meta_page(cpu_buffer);
+ atomic_dec(&cpu_buffer->resize_disabled);
+
+ mutex_unlock(&buffer->mutex);
+out:
+ mutex_unlock(&cpu_buffer->mapping_lock);
+
+ return err;
+}
+
+/*
+ * +--------------+ pgoff == 0
+ * | meta page |
+ * +--------------+ pgoff == 1
+ * | subbuffer 0 |
+ * +--------------+ pgoff == 1 + (1 << subbuf_order)
+ * | subbuffer 1 |
+ * ...
+ */
+struct page *ring_buffer_map_fault(struct trace_buffer *buffer, int cpu,
+ unsigned long pgoff)
+{
+ struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
+ unsigned long subbuf_id, subbuf_offset, addr;
+ struct page *page;
+
+ if (!pgoff)
+ return virt_to_page((void *)cpu_buffer->meta_page);
+
+ pgoff--;
+
+ subbuf_id = pgoff >> buffer->subbuf_order;
+ if (subbuf_id > cpu_buffer->nr_pages)
+ return NULL;
+
+ subbuf_offset = pgoff & ((1UL << buffer->subbuf_order) - 1);
+ addr = cpu_buffer->subbuf_ids[subbuf_id] + (subbuf_offset * PAGE_SIZE);
+ page = virt_to_page((void *)addr);
+
+ return page;
+}
+
+int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu)
+{
+ struct ring_buffer_per_cpu *cpu_buffer;
+ unsigned long reader_size;
+ unsigned long flags;
+
+ cpu_buffer = rb_get_mapped_buffer(buffer, cpu);
+ if (IS_ERR(cpu_buffer))
+ return (int)PTR_ERR(cpu_buffer);
+
+ raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+consume:
+ if (rb_per_cpu_empty(cpu_buffer))
+ goto out;
+
+ reader_size = rb_page_size(cpu_buffer->reader_page);
+
+ /*
+ * There are data to be read on the current reader page, we can
+ * return to the caller. But before that, we assume the latter will read
+ * everything. Let's update the kernel reader accordingly.
+ */
+ if (cpu_buffer->reader_page->read < reader_size) {
+ while (cpu_buffer->reader_page->read < reader_size)
+ rb_advance_reader(cpu_buffer);
+ goto out;
+ }
+
+ if (WARN_ON(!rb_get_reader_page(cpu_buffer)))
+ goto out;
+
+ goto consume;
+out:
+ rb_update_meta_page(cpu_buffer);
+ raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+ rb_put_mapped_buffer(cpu_buffer);
+
+ return 0;
+}
+
/*
* We only allocate new buffers, never free them if the CPU goes down.
* If we were to free the buffer, then the user would lose any trace that was in
--
2.43.0.594.gd9cf4e227d-goog
When a ring-buffer is memory mapped by user-space, no trace or
ring-buffer swap is possible. This means the snapshot feature is
mutually exclusive with the memory mapping. Having a refcount on
snapshot users will help to know if a mapping is possible or not.
Instead of relying on the global trace_types_lock, a new spinlock is
introduced to serialize accesses to trace_array->snapshot. This intends
to allow access to that variable in a context where the mmap lock is
already held.
Signed-off-by: Vincent Donnefort <[email protected]>
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 2a7c6fd934e9..4ebf4d0bd14c 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1300,6 +1300,50 @@ static void free_snapshot(struct trace_array *tr)
tr->allocated_snapshot = false;
}
+static int tracing_arm_snapshot_locked(struct trace_array *tr)
+{
+ int ret;
+
+ lockdep_assert_held(&trace_types_lock);
+
+ spin_lock(&tr->snapshot_trigger_lock);
+ if (tr->snapshot == UINT_MAX) {
+ spin_unlock(&tr->snapshot_trigger_lock);
+ return -EBUSY;
+ }
+
+ tr->snapshot++;
+ spin_unlock(&tr->snapshot_trigger_lock);
+
+ ret = tracing_alloc_snapshot_instance(tr);
+ if (ret) {
+ spin_lock(&tr->snapshot_trigger_lock);
+ tr->snapshot--;
+ spin_unlock(&tr->snapshot_trigger_lock);
+ }
+
+ return ret;
+}
+
+int tracing_arm_snapshot(struct trace_array *tr)
+{
+ int ret;
+
+ mutex_lock(&trace_types_lock);
+ ret = tracing_arm_snapshot_locked(tr);
+ mutex_unlock(&trace_types_lock);
+
+ return ret;
+}
+
+void tracing_disarm_snapshot(struct trace_array *tr)
+{
+ spin_lock(&tr->snapshot_trigger_lock);
+ if (!WARN_ON(!tr->snapshot))
+ tr->snapshot--;
+ spin_unlock(&tr->snapshot_trigger_lock);
+}
+
/**
* tracing_alloc_snapshot - allocate snapshot buffer.
*
@@ -1373,10 +1417,6 @@ int tracing_snapshot_cond_enable(struct trace_array *tr, void *cond_data,
mutex_lock(&trace_types_lock);
- ret = tracing_alloc_snapshot_instance(tr);
- if (ret)
- goto fail_unlock;
-
if (tr->current_trace->use_max_tr) {
ret = -EBUSY;
goto fail_unlock;
@@ -1395,6 +1435,10 @@ int tracing_snapshot_cond_enable(struct trace_array *tr, void *cond_data,
goto fail_unlock;
}
+ ret = tracing_arm_snapshot_locked(tr);
+ if (ret)
+ goto fail_unlock;
+
local_irq_disable();
arch_spin_lock(&tr->max_lock);
tr->cond_snapshot = cond_snapshot;
@@ -1439,6 +1483,8 @@ int tracing_snapshot_cond_disable(struct trace_array *tr)
arch_spin_unlock(&tr->max_lock);
local_irq_enable();
+ tracing_disarm_snapshot(tr);
+
return ret;
}
EXPORT_SYMBOL_GPL(tracing_snapshot_cond_disable);
@@ -1481,6 +1527,7 @@ int tracing_snapshot_cond_disable(struct trace_array *tr)
}
EXPORT_SYMBOL_GPL(tracing_snapshot_cond_disable);
#define free_snapshot(tr) do { } while (0)
+#define tracing_arm_snapshot_locked(tr) ({ -EBUSY; })
#endif /* CONFIG_TRACER_SNAPSHOT */
void tracer_tracing_off(struct trace_array *tr)
@@ -6593,11 +6640,12 @@ int tracing_set_tracer(struct trace_array *tr, const char *buf)
*/
synchronize_rcu();
free_snapshot(tr);
+ tracing_disarm_snapshot(tr);
}
- if (t->use_max_tr && !tr->allocated_snapshot) {
- ret = tracing_alloc_snapshot_instance(tr);
- if (ret < 0)
+ if (t->use_max_tr) {
+ ret = tracing_arm_snapshot_locked(tr);
+ if (ret)
goto out;
}
#else
@@ -6606,8 +6654,13 @@ int tracing_set_tracer(struct trace_array *tr, const char *buf)
if (t->init) {
ret = tracer_init(t, tr);
- if (ret)
+ if (ret) {
+#ifdef CONFIG_TRACER_MAX_TRACE
+ if (t->use_max_tr)
+ tracing_disarm_snapshot(tr);
+#endif
goto out;
+ }
}
tr->current_trace = t;
@@ -7709,10 +7762,11 @@ tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt,
if (tr->allocated_snapshot)
ret = resize_buffer_duplicate_size(&tr->max_buffer,
&tr->array_buffer, iter->cpu_file);
- else
- ret = tracing_alloc_snapshot_instance(tr);
- if (ret < 0)
+
+ ret = tracing_arm_snapshot_locked(tr);
+ if (ret)
break;
+
/* Now, we're going to swap */
if (iter->cpu_file == RING_BUFFER_ALL_CPUS) {
local_irq_disable();
@@ -7722,6 +7776,7 @@ tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt,
smp_call_function_single(iter->cpu_file, tracing_swap_cpu_buffer,
(void *)tr, 1);
}
+ tracing_disarm_snapshot(tr);
break;
default:
if (tr->allocated_snapshot) {
@@ -8846,8 +8901,13 @@ ftrace_trace_snapshot_callback(struct trace_array *tr, struct ftrace_hash *hash,
ops = param ? &snapshot_count_probe_ops : &snapshot_probe_ops;
- if (glob[0] == '!')
- return unregister_ftrace_function_probe_func(glob+1, tr, ops);
+ if (glob[0] == '!') {
+ ret = unregister_ftrace_function_probe_func(glob+1, tr, ops);
+ if (!ret)
+ tracing_disarm_snapshot(tr);
+
+ return ret;
+ }
if (!param)
goto out_reg;
@@ -8866,12 +8926,13 @@ ftrace_trace_snapshot_callback(struct trace_array *tr, struct ftrace_hash *hash,
return ret;
out_reg:
- ret = tracing_alloc_snapshot_instance(tr);
+ ret = tracing_arm_snapshot(tr);
if (ret < 0)
goto out;
ret = register_ftrace_function_probe(glob, tr, ops, count);
-
+ if (ret < 0)
+ tracing_disarm_snapshot(tr);
out:
return ret < 0 ? ret : 0;
}
@@ -9678,7 +9739,9 @@ trace_array_create_systems(const char *name, const char *systems)
raw_spin_lock_init(&tr->start_lock);
tr->max_lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
-
+#ifdef CONFIG_TRCER_MAX_TRACE
+ spinlock_init(&tr->snapshot_trigger_lock);
+#endif
tr->current_trace = &nop_trace;
INIT_LIST_HEAD(&tr->systems);
@@ -10648,7 +10711,9 @@ __init static int tracer_alloc_buffers(void)
global_trace.current_trace = &nop_trace;
global_trace.max_lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
-
+#ifdef CONFIG_TRACER_MAX_TRACE
+ spin_lock_init(&global_trace.snapshot_trigger_lock);
+#endif
ftrace_init_global_array_ops(&global_trace);
init_trace_flags_index(&global_trace);
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 00f873910c5d..bd312e9afe25 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -334,8 +334,8 @@ struct trace_array {
*/
struct array_buffer max_buffer;
bool allocated_snapshot;
-#endif
-#ifdef CONFIG_TRACER_MAX_TRACE
+ spinlock_t snapshot_trigger_lock;
+ unsigned int snapshot;
unsigned long max_latency;
#ifdef CONFIG_FSNOTIFY
struct dentry *d_max_latency;
@@ -1973,12 +1973,16 @@ static inline void trace_event_eval_update(struct trace_eval_map **map, int len)
#ifdef CONFIG_TRACER_SNAPSHOT
void tracing_snapshot_instance(struct trace_array *tr);
int tracing_alloc_snapshot_instance(struct trace_array *tr);
+int tracing_arm_snapshot(struct trace_array *tr);
+void tracing_disarm_snapshot(struct trace_array *tr);
#else
static inline void tracing_snapshot_instance(struct trace_array *tr) { }
static inline int tracing_alloc_snapshot_instance(struct trace_array *tr)
{
return 0;
}
+static inline int tracing_arm_snapshot(struct trace_array *tr) { return 0; }
+static inline void tracing_disarm_snapshot(struct trace_array *tr) { }
#endif
#ifdef CONFIG_PREEMPT_TRACER
diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
index b33c3861fbbb..62e4f58b8671 100644
--- a/kernel/trace/trace_events_trigger.c
+++ b/kernel/trace/trace_events_trigger.c
@@ -597,20 +597,12 @@ static int register_trigger(char *glob,
return ret;
}
-/**
- * unregister_trigger - Generic event_command @unreg implementation
- * @glob: The raw string used to register the trigger
- * @test: Trigger-specific data used to find the trigger to remove
- * @file: The trace_event_file associated with the event
- *
- * Common implementation for event trigger unregistration.
- *
- * Usually used directly as the @unreg method in event command
- * implementations.
+/*
+ * True if the trigger was found and unregistered, else false.
*/
-static void unregister_trigger(char *glob,
- struct event_trigger_data *test,
- struct trace_event_file *file)
+static bool try_unregister_trigger(char *glob,
+ struct event_trigger_data *test,
+ struct trace_event_file *file)
{
struct event_trigger_data *data = NULL, *iter;
@@ -626,8 +618,32 @@ static void unregister_trigger(char *glob,
}
}
- if (data && data->ops->free)
- data->ops->free(data);
+ if (data) {
+ if (data->ops->free)
+ data->ops->free(data);
+
+ return true;
+ }
+
+ return false;
+}
+
+/**
+ * unregister_trigger - Generic event_command @unreg implementation
+ * @glob: The raw string used to register the trigger
+ * @test: Trigger-specific data used to find the trigger to remove
+ * @file: The trace_event_file associated with the event
+ *
+ * Common implementation for event trigger unregistration.
+ *
+ * Usually used directly as the @unreg method in event command
+ * implementations.
+ */
+static void unregister_trigger(char *glob,
+ struct event_trigger_data *test,
+ struct trace_event_file *file)
+{
+ try_unregister_trigger(glob, test, file);
}
/*
@@ -1470,7 +1486,7 @@ register_snapshot_trigger(char *glob,
struct event_trigger_data *data,
struct trace_event_file *file)
{
- int ret = tracing_alloc_snapshot_instance(file->tr);
+ int ret = tracing_arm_snapshot(file->tr);
if (ret < 0)
return ret;
@@ -1478,6 +1494,14 @@ register_snapshot_trigger(char *glob,
return register_trigger(glob, data, file);
}
+static void unregister_snapshot_trigger(char *glob,
+ struct event_trigger_data *data,
+ struct trace_event_file *file)
+{
+ if (try_unregister_trigger(glob, data, file))
+ tracing_disarm_snapshot(file->tr);
+}
+
static int
snapshot_trigger_print(struct seq_file *m, struct event_trigger_data *data)
{
@@ -1510,7 +1534,7 @@ static struct event_command trigger_snapshot_cmd = {
.trigger_type = ETT_SNAPSHOT,
.parse = event_trigger_parse,
.reg = register_snapshot_trigger,
- .unreg = unregister_trigger,
+ .unreg = unregister_snapshot_trigger,
.get_trigger_ops = snapshot_get_trigger_ops,
.set_filter = set_trigger_filter,
};
--
2.43.0.594.gd9cf4e227d-goog
Currently, user-space extracts data from the ring-buffer via splice,
which is handy for storage or network sharing. However, due to splice
limitations, it is imposible to do real-time analysis without a copy.
A solution for that problem is to let the user-space map the ring-buffer
directly.
The mapping is exposed via the per-CPU file trace_pipe_raw. The first
element of the mapping is the meta-page. It is followed by each
subbuffer constituting the ring-buffer, ordered by their unique page ID:
* Meta-page -- include/uapi/linux/trace_mmap.h for a description
* Subbuf ID 0
* Subbuf ID 1
...
It is therefore easy to translate a subbuf ID into an offset in the
mapping:
reader_id = meta->reader->id;
reader_offset = meta->meta_page_size + reader_id * meta->subbuf_size;
When new data is available, the mapper must call a newly introduced ioctl:
TRACE_MMAP_IOCTL_GET_READER. This will update the Meta-page reader ID to
point to the next reader containing unread data.
Mapping will prevent snapshot and buffer size modifications.
Signed-off-by: Vincent Donnefort <[email protected]>
diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mmap.h
index 182e05a3004a..7330249257e7 100644
--- a/include/uapi/linux/trace_mmap.h
+++ b/include/uapi/linux/trace_mmap.h
@@ -43,4 +43,6 @@ struct trace_buffer_meta {
__u64 Reserved2;
};
+#define TRACE_MMAP_IOCTL_GET_READER _IO('T', 0x1)
+
#endif /* _TRACE_MMAP_H_ */
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 4ebf4d0bd14c..36b62cf2fb3f 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1175,6 +1175,12 @@ static void tracing_snapshot_instance_cond(struct trace_array *tr,
return;
}
+ if (tr->mapped) {
+ trace_array_puts(tr, "*** BUFFER MEMORY MAPPED ***\n");
+ trace_array_puts(tr, "*** Can not use snapshot (sorry) ***\n");
+ return;
+ }
+
local_irq_save(flags);
update_max_tr(tr, current, smp_processor_id(), cond_data);
local_irq_restore(flags);
@@ -1307,7 +1313,7 @@ static int tracing_arm_snapshot_locked(struct trace_array *tr)
lockdep_assert_held(&trace_types_lock);
spin_lock(&tr->snapshot_trigger_lock);
- if (tr->snapshot == UINT_MAX) {
+ if (tr->snapshot == UINT_MAX || tr->mapped) {
spin_unlock(&tr->snapshot_trigger_lock);
return -EBUSY;
}
@@ -6533,7 +6539,7 @@ static void tracing_set_nop(struct trace_array *tr)
{
if (tr->current_trace == &nop_trace)
return;
-
+
tr->current_trace->enabled--;
if (tr->current_trace->reset)
@@ -8652,15 +8658,31 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
return ret;
}
-/* An ioctl call with cmd 0 to the ring buffer file will wake up all waiters */
static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
struct ftrace_buffer_info *info = file->private_data;
struct trace_iterator *iter = &info->iter;
+ int err;
+
+ if (cmd == TRACE_MMAP_IOCTL_GET_READER) {
+ if (!(file->f_flags & O_NONBLOCK)) {
+ err = ring_buffer_wait(iter->array_buffer->buffer,
+ iter->cpu_file,
+ iter->tr->buffer_percent);
+ if (err)
+ return err;
+ }
- if (cmd)
- return -ENOIOCTLCMD;
+ return ring_buffer_map_get_reader(iter->array_buffer->buffer,
+ iter->cpu_file);
+ } else if (cmd) {
+ return -ENOTTY;
+ }
+ /*
+ * An ioctl call with cmd 0 to the ring buffer file will wake up all
+ * waiters
+ */
mutex_lock(&trace_types_lock);
iter->wait_index++;
@@ -8673,6 +8695,97 @@ static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, unsigned
return 0;
}
+static vm_fault_t tracing_buffers_mmap_fault(struct vm_fault *vmf)
+{
+ struct ftrace_buffer_info *info = vmf->vma->vm_file->private_data;
+ struct trace_iterator *iter = &info->iter;
+ vm_fault_t ret = VM_FAULT_SIGBUS;
+ struct page *page;
+
+ page = ring_buffer_map_fault(iter->array_buffer->buffer, iter->cpu_file,
+ vmf->pgoff);
+ if (!page)
+ return ret;
+
+ get_page(page);
+ vmf->page = page;
+ vmf->page->mapping = vmf->vma->vm_file->f_mapping;
+ vmf->page->index = vmf->pgoff;
+
+ return 0;
+}
+
+static void tracing_buffers_mmap_close(struct vm_area_struct *vma)
+{
+ struct ftrace_buffer_info *info = vma->vm_file->private_data;
+ struct trace_iterator *iter = &info->iter;
+ struct trace_array *tr = iter->tr;
+
+ ring_buffer_unmap(iter->array_buffer->buffer, iter->cpu_file);
+
+#ifdef CONFIG_TRACER_MAX_TRACE
+ spin_lock(&tr->snapshot_trigger_lock);
+ if (!WARN_ON(!tr->mapped))
+ tr->mapped--;
+ spin_unlock(&tr->snapshot_trigger_lock);
+#endif
+}
+
+static void tracing_buffers_mmap_open(struct vm_area_struct *vma)
+{
+ struct ftrace_buffer_info *info = vma->vm_file->private_data;
+ struct trace_iterator *iter = &info->iter;
+
+ WARN_ON(ring_buffer_map(iter->array_buffer->buffer, iter->cpu_file));
+}
+
+static const struct vm_operations_struct tracing_buffers_vmops = {
+ .open = tracing_buffers_mmap_open,
+ .close = tracing_buffers_mmap_close,
+ .fault = tracing_buffers_mmap_fault,
+};
+
+static int tracing_buffers_mmap(struct file *filp, struct vm_area_struct *vma)
+{
+ struct ftrace_buffer_info *info = filp->private_data;
+ struct trace_iterator *iter = &info->iter;
+ struct trace_array *tr = iter->tr;
+ int ret = 0;
+
+ if (vma->vm_flags & VM_WRITE)
+ return -EPERM;
+
+ vm_flags_mod(vma, VM_DONTCOPY | VM_DONTDUMP, VM_MAYWRITE);
+ vma->vm_ops = &tracing_buffers_vmops;
+
+#ifdef CONFIG_TRACER_MAX_TRACE
+ /*
+ * We hold mmap_lock here. lockdep would be unhappy if we would now take
+ * trace_types_lock. Instead use the specific snapshot_trigger_lock.
+ */
+ spin_lock(&tr->snapshot_trigger_lock);
+ if (tr->snapshot || tr->mapped == UINT_MAX) {
+ spin_unlock(&tr->snapshot_trigger_lock);
+ return -EBUSY;
+ }
+ tr->mapped++;
+ spin_unlock(&tr->snapshot_trigger_lock);
+
+ /* Wait for update_max_tr() to observe iter->tr->mapped */
+ if (tr->mapped == 1)
+ synchronize_rcu();
+#endif
+ ret = ring_buffer_map(iter->array_buffer->buffer, iter->cpu_file);
+#ifdef CONFIG_TRACER_MAX_TRACE
+ if (ret) {
+ spin_lock(&tr->snapshot_trigger_lock);
+ iter->tr->mapped--;
+ spin_unlock(&tr->snapshot_trigger_lock);
+ }
+#endif
+ return ret;
+}
+
static const struct file_operations tracing_buffers_fops = {
.open = tracing_buffers_open,
.read = tracing_buffers_read,
@@ -8681,6 +8794,7 @@ static const struct file_operations tracing_buffers_fops = {
.splice_read = tracing_buffers_splice_read,
.unlocked_ioctl = tracing_buffers_ioctl,
.llseek = no_llseek,
+ .mmap = tracing_buffers_mmap,
};
static ssize_t
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index bd312e9afe25..8a96e7a89e6b 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -336,6 +336,7 @@ struct trace_array {
bool allocated_snapshot;
spinlock_t snapshot_trigger_lock;
unsigned int snapshot;
+ unsigned int mapped;
unsigned long max_latency;
#ifdef CONFIG_FSNOTIFY
struct dentry *d_max_latency;
--
2.43.0.594.gd9cf4e227d-goog
It is now possible to mmap() a ring-buffer to stream its content. Add
some documentation and a code example.
Signed-off-by: Vincent Donnefort <[email protected]>
diff --git a/Documentation/trace/index.rst b/Documentation/trace/index.rst
index 5092d6c13af5..0b300901fd75 100644
--- a/Documentation/trace/index.rst
+++ b/Documentation/trace/index.rst
@@ -29,6 +29,7 @@ Linux Tracing Technologies
timerlat-tracer
intel_th
ring-buffer-design
+ ring-buffer-map
stm
sys-t
coresight/index
diff --git a/Documentation/trace/ring-buffer-map.rst b/Documentation/trace/ring-buffer-map.rst
new file mode 100644
index 000000000000..628254e63830
--- /dev/null
+++ b/Documentation/trace/ring-buffer-map.rst
@@ -0,0 +1,104 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==================================
+Tracefs ring-buffer memory mapping
+==================================
+
+:Author: Vincent Donnefort <[email protected]>
+
+Overview
+========
+Tracefs ring-buffer memory map provides an efficient method to stream data
+as no memory copy is necessary. The application mapping the ring-buffer becomes
+then a consumer for that ring-buffer, in a similar fashion to trace_pipe.
+
+Memory mapping setup
+====================
+The mapping works with a mmap() of the trace_pipe_raw interface.
+
+The first system page of the mapping contains ring-buffer statistics and
+description. It is referred as the meta-page. One of the most important field of
+the meta-page is the reader. It contains the sub-buffer ID which can be safely
+read by the mapper (see ring-buffer-design.rst).
+
+The meta-page is followed by all the sub-buffers, ordered by ascendant ID. It is
+therefore effortless to know where the reader starts in the mapping:
+
+.. code-block:: c
+
+ reader_id = meta->reader->id;
+ reader_offset = meta->meta_page_size + reader_id * meta->subbuf_size;
+
+When the application is done with the current reader, it can get a new one using
+the trace_pipe_raw ioctl() TRACE_MMAP_IOCTL_GET_READER. This ioctl also updates
+the meta-page fields.
+
+Limitations
+===========
+When a mapping is in place on a Tracefs ring-buffer, it is not possible to
+either resize it (either by increasing the entire size of the ring-buffer or
+each subbuf). It is also not possible to use snapshot or splice.
+
+Concurrent readers (either another application mapping that ring-buffer or the
+kernel with trace_pipe) are allowed but not recommended. They will compete for
+the ring-buffer and the output is unpredictable.
+
+Example
+=======
+
+.. code-block:: c
+
+ #include <fcntl.h>
+ #include <stdio.h>
+ #include <stdlib.h>
+ #include <unistd.h>
+
+ #include <linux/trace_mmap.h>
+
+ #include <sys/mman.h>
+ #include <sys/ioctl.h>
+
+ #define TRACE_PIPE_RAW "/sys/kernel/tracing/per_cpu/cpu0/trace_pipe_raw"
+
+ int main(void)
+ {
+ int page_size = getpagesize(), fd, reader_id;
+ unsigned long meta_len, data_len;
+ struct trace_buffer_meta *meta;
+ void *map, *reader, *data;
+
+ fd = open(TRACE_PIPE_RAW, O_RDONLY | O_NONBLOCK);
+ if (fd < 0)
+ exit(EXIT_FAILURE);
+
+ map = mmap(NULL, page_size, PROT_READ, MAP_SHARED, fd, 0);
+ if (map == MAP_FAILED)
+ exit(EXIT_FAILURE);
+
+ meta = (struct trace_buffer_meta *)map;
+ meta_len = meta->meta_page_size;
+
+ printf("entries: %llu\n", meta->entries);
+ printf("overrun: %llu\n", meta->overrun);
+ printf("read: %llu\n", meta->read);
+ printf("nr_subbufs: %u\n", meta->nr_subbufs);
+
+ data_len = meta->subbuf_size * meta->nr_subbufs;
+ data = mmap(NULL, data_len, PROT_READ, MAP_SHARED, fd, meta_len);
+ if (data == MAP_FAILED)
+ exit(EXIT_FAILURE);
+
+ if (ioctl(fd, TRACE_MMAP_IOCTL_GET_READER) < 0)
+ exit(EXIT_FAILURE);
+
+ reader_id = meta->reader.id;
+ reader = data + meta->subbuf_size * reader_id;
+
+ printf("Current reader address: %p\n", reader);
+
+ munmap(data, data_len);
+ munmap(meta, meta_len);
+ close (fd);
+
+ return 0;
+ }
--
2.43.0.594.gd9cf4e227d-goog
This test maps a ring-buffer and validate the meta-page after reset and
after emitting few events.
Cc: Shuah Khan <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: [email protected]
Signed-off-by: Vincent Donnefort <[email protected]>
diff --git a/tools/testing/selftests/ring-buffer/Makefile b/tools/testing/selftests/ring-buffer/Makefile
new file mode 100644
index 000000000000..627c5fa6d1ab
--- /dev/null
+++ b/tools/testing/selftests/ring-buffer/Makefile
@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: GPL-2.0
+CFLAGS += -Wl,-no-as-needed -Wall
+CFLAGS += $(KHDR_INCLUDES)
+CFLAGS += -D_GNU_SOURCE
+
+TEST_GEN_PROGS = map_test
+
+include ../lib.mk
diff --git a/tools/testing/selftests/ring-buffer/config b/tools/testing/selftests/ring-buffer/config
new file mode 100644
index 000000000000..d936f8f00e78
--- /dev/null
+++ b/tools/testing/selftests/ring-buffer/config
@@ -0,0 +1,2 @@
+CONFIG_FTRACE=y
+CONFIG_TRACER_SNAPSHOT=y
diff --git a/tools/testing/selftests/ring-buffer/map_test.c b/tools/testing/selftests/ring-buffer/map_test.c
new file mode 100644
index 000000000000..56c44b29d998
--- /dev/null
+++ b/tools/testing/selftests/ring-buffer/map_test.c
@@ -0,0 +1,273 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Ring-buffer memory mapping tests
+ *
+ * Copyright (c) 2024 Vincent Donnefort <[email protected]>
+ */
+#include <fcntl.h>
+#include <sched.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include <linux/trace_mmap.h>
+
+#include <sys/mman.h>
+#include <sys/ioctl.h>
+
+#include "../user_events/user_events_selftests.h" /* share tracefs setup */
+#include "../kselftest_harness.h"
+
+#define TRACEFS_ROOT "/sys/kernel/tracing"
+
+static int __tracefs_write(const char *path, const char *value)
+{
+ int fd, ret;
+
+ fd = open(path, O_WRONLY | O_TRUNC);
+ if (fd < 0)
+ return fd;
+
+ ret = write(fd, value, strlen(value));
+
+ close(fd);
+
+ return ret == -1 ? -errno : 0;
+}
+
+static int __tracefs_write_int(const char *path, int value)
+{
+ char *str;
+ int ret;
+
+ if (asprintf(&str, "%d", value) < 0)
+ return -1;
+
+ ret = __tracefs_write(path, str);
+
+ free(str);
+
+ return ret;
+}
+
+#define tracefs_write_int(path, value) \
+ ASSERT_EQ(__tracefs_write_int((path), (value)), 0)
+
+#define tracefs_write(path, value) \
+ ASSERT_EQ(__tracefs_write((path), (value)), 0)
+
+static int tracefs_reset(void)
+{
+ if (__tracefs_write_int(TRACEFS_ROOT"/tracing_on", 0))
+ return -1;
+ if (__tracefs_write(TRACEFS_ROOT"/trace", ""))
+ return -1;
+ if (__tracefs_write(TRACEFS_ROOT"/set_event", ""))
+ return -1;
+ if (__tracefs_write(TRACEFS_ROOT"/current_tracer", "nop"))
+ return -1;
+
+ return 0;
+}
+
+struct tracefs_cpu_map_desc {
+ struct trace_buffer_meta *meta;
+ void *data;
+ int cpu_fd;
+};
+
+int tracefs_cpu_map(struct tracefs_cpu_map_desc *desc, int cpu)
+{
+ unsigned long meta_len, data_len;
+ int page_size = getpagesize();
+ char *cpu_path;
+ void *map;
+
+ if (asprintf(&cpu_path,
+ TRACEFS_ROOT"/per_cpu/cpu%d/trace_pipe_raw",
+ cpu) < 0)
+ return -ENOMEM;
+
+ desc->cpu_fd = open(cpu_path, O_RDONLY | O_NONBLOCK);
+ free(cpu_path);
+ if (desc->cpu_fd < 0)
+ return -ENODEV;
+
+ map = mmap(NULL, page_size, PROT_READ, MAP_SHARED, desc->cpu_fd, 0);
+ if (map == MAP_FAILED)
+ return -errno;
+
+ desc->meta = (struct trace_buffer_meta *)map;
+
+ meta_len = desc->meta->meta_page_size;
+ data_len = desc->meta->subbuf_size * desc->meta->nr_subbufs;
+
+ map = mmap(NULL, data_len, PROT_READ, MAP_SHARED, desc->cpu_fd, meta_len);
+ if (map == MAP_FAILED) {
+ munmap(desc->meta, desc->meta->meta_page_size);
+ return -EINVAL;
+ }
+
+ desc->data = map;
+
+ return 0;
+}
+
+void tracefs_cpu_unmap(struct tracefs_cpu_map_desc *desc)
+{
+ munmap(desc->data, desc->meta->subbuf_size * desc->meta->nr_subbufs);
+ munmap(desc->meta, desc->meta->meta_page_size);
+ close(desc->cpu_fd);
+}
+
+FIXTURE(map) {
+ struct tracefs_cpu_map_desc map_desc;
+ bool umount;
+};
+
+FIXTURE_VARIANT(map) {
+ int subbuf_size;
+};
+
+FIXTURE_VARIANT_ADD(map, subbuf_size_4k) {
+ .subbuf_size = 4,
+};
+
+FIXTURE_VARIANT_ADD(map, subbuf_size_8k) {
+ .subbuf_size = 8,
+};
+
+FIXTURE_SETUP(map)
+{
+ int cpu = sched_getcpu();
+ cpu_set_t cpu_mask;
+ bool fail, umount;
+ char *message;
+
+ if (!tracefs_enabled(&message, &fail, &umount)) {
+ if (fail) {
+ TH_LOG("Tracefs setup failed: %s", message);
+ ASSERT_FALSE(fail);
+ }
+ SKIP(return, "Skipping: %s", message);
+ }
+
+ self->umount = umount;
+
+ ASSERT_GE(cpu, 0);
+
+ ASSERT_EQ(tracefs_reset(), 0);
+
+ tracefs_write_int(TRACEFS_ROOT"/buffer_subbuf_size_kb", variant->subbuf_size);
+
+ ASSERT_EQ(tracefs_cpu_map(&self->map_desc, cpu), 0);
+
+ /*
+ * Ensure generated events will be found on this very same ring-buffer.
+ */
+ CPU_ZERO(&cpu_mask);
+ CPU_SET(cpu, &cpu_mask);
+ ASSERT_EQ(sched_setaffinity(0, sizeof(cpu_mask), &cpu_mask), 0);
+}
+
+FIXTURE_TEARDOWN(map)
+{
+ tracefs_reset();
+
+ if (self->umount)
+ tracefs_unmount();
+
+ tracefs_cpu_unmap(&self->map_desc);
+}
+
+TEST_F(map, meta_page_check)
+{
+ struct tracefs_cpu_map_desc *desc = &self->map_desc;
+ int cnt = 0;
+
+ ASSERT_EQ(desc->meta->entries, 0);
+ ASSERT_EQ(desc->meta->overrun, 0);
+ ASSERT_EQ(desc->meta->read, 0);
+
+ ASSERT_EQ(desc->meta->reader.id, 0);
+ ASSERT_EQ(desc->meta->reader.read, 0);
+
+ ASSERT_EQ(ioctl(desc->cpu_fd, TRACE_MMAP_IOCTL_GET_READER), 0);
+ ASSERT_EQ(desc->meta->reader.id, 0);
+
+ tracefs_write_int(TRACEFS_ROOT"/tracing_on", 1);
+ for (int i = 0; i < 16; i++)
+ tracefs_write_int(TRACEFS_ROOT"/trace_marker", i);
+again:
+ ASSERT_EQ(ioctl(desc->cpu_fd, TRACE_MMAP_IOCTL_GET_READER), 0);
+
+ ASSERT_EQ(desc->meta->entries, 16);
+ ASSERT_EQ(desc->meta->overrun, 0);
+ ASSERT_EQ(desc->meta->read, 16);
+
+ ASSERT_EQ(desc->meta->reader.id, 1);
+
+ if (!(cnt++))
+ goto again;
+}
+
+FIXTURE(snapshot) {
+ bool umount;
+};
+
+FIXTURE_SETUP(snapshot)
+{
+ bool fail, umount;
+ struct stat sb;
+ char *message;
+
+ if (stat(TRACEFS_ROOT"/snapshot", &sb))
+ SKIP(return, "Skipping: %s", "snapshot not available");
+
+ if (!tracefs_enabled(&message, &fail, &umount)) {
+ if (fail) {
+ TH_LOG("Tracefs setup failed: %s", message);
+ ASSERT_FALSE(fail);
+ }
+ SKIP(return, "Skipping: %s", message);
+ }
+
+ self->umount = umount;
+}
+
+FIXTURE_TEARDOWN(snapshot)
+{
+ __tracefs_write(TRACEFS_ROOT"/events/sched/sched_switch/trigger",
+ "!snapshot");
+ tracefs_reset();
+
+ if (self->umount)
+ tracefs_unmount();
+}
+
+TEST_F(snapshot, excludes_map)
+{
+ struct tracefs_cpu_map_desc map_desc;
+ int cpu = sched_getcpu();
+
+ ASSERT_GE(cpu, 0);
+ tracefs_write(TRACEFS_ROOT"/events/sched/sched_switch/trigger",
+ "snapshot");
+ ASSERT_EQ(tracefs_cpu_map(&map_desc, cpu), -EBUSY);
+}
+
+TEST_F(snapshot, excluded_by_map)
+{
+ struct tracefs_cpu_map_desc map_desc;
+ int cpu = sched_getcpu();
+
+ ASSERT_EQ(tracefs_cpu_map(&map_desc, cpu), 0);
+
+ ASSERT_EQ(__tracefs_write(TRACEFS_ROOT"/events/sched/sched_switch/trigger",
+ "snapshot"), -EBUSY);
+ ASSERT_EQ(__tracefs_write(TRACEFS_ROOT"/snapshot",
+ "1"), -EBUSY);
+}
+
+TEST_HARNESS_MAIN
--
2.43.0.594.gd9cf4e227d-goog
On 2024-02-05 11:34, Vincent Donnefort wrote:
> Currently, user-space extracts data from the ring-buffer via splice,
> which is handy for storage or network sharing. However, due to splice
> limitations, it is imposible to do real-time analysis without a copy.
>
> A solution for that problem is to let the user-space map the ring-buffer
> directly.
>
> The mapping is exposed via the per-CPU file trace_pipe_raw. The first
> element of the mapping is the meta-page. It is followed by each
> subbuffer constituting the ring-buffer, ordered by their unique page ID:
>
> * Meta-page -- include/uapi/linux/trace_mmap.h for a description
> * Subbuf ID 0
> * Subbuf ID 1
> ...
>
> It is therefore easy to translate a subbuf ID into an offset in the
> mapping:
>
> reader_id = meta->reader->id;
> reader_offset = meta->meta_page_size + reader_id * meta->subbuf_size;
>
> When new data is available, the mapper must call a newly introduced ioctl:
> TRACE_MMAP_IOCTL_GET_READER. This will update the Meta-page reader ID to
> point to the next reader containing unread data.
>
> Mapping will prevent snapshot and buffer size modifications.
How are the kernel linear mapping and the userspace mapping made coherent
on architectures with virtually aliasing data caches ?
Ref. https://lore.kernel.org/lkml/[email protected]/T/#t
Thanks,
Mathieu
>
> Signed-off-by: Vincent Donnefort <[email protected]>
>
> diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mmap.h
> index 182e05a3004a..7330249257e7 100644
> --- a/include/uapi/linux/trace_mmap.h
> +++ b/include/uapi/linux/trace_mmap.h
> @@ -43,4 +43,6 @@ struct trace_buffer_meta {
> __u64 Reserved2;
> };
>
> +#define TRACE_MMAP_IOCTL_GET_READER _IO('T', 0x1)
> +
> #endif /* _TRACE_MMAP_H_ */
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 4ebf4d0bd14c..36b62cf2fb3f 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -1175,6 +1175,12 @@ static void tracing_snapshot_instance_cond(struct trace_array *tr,
> return;
> }
>
> + if (tr->mapped) {
> + trace_array_puts(tr, "*** BUFFER MEMORY MAPPED ***\n");
> + trace_array_puts(tr, "*** Can not use snapshot (sorry) ***\n");
> + return;
> + }
> +
> local_irq_save(flags);
> update_max_tr(tr, current, smp_processor_id(), cond_data);
> local_irq_restore(flags);
> @@ -1307,7 +1313,7 @@ static int tracing_arm_snapshot_locked(struct trace_array *tr)
> lockdep_assert_held(&trace_types_lock);
>
> spin_lock(&tr->snapshot_trigger_lock);
> - if (tr->snapshot == UINT_MAX) {
> + if (tr->snapshot == UINT_MAX || tr->mapped) {
> spin_unlock(&tr->snapshot_trigger_lock);
> return -EBUSY;
> }
> @@ -6533,7 +6539,7 @@ static void tracing_set_nop(struct trace_array *tr)
> {
> if (tr->current_trace == &nop_trace)
> return;
> -
> +
> tr->current_trace->enabled--;
>
> if (tr->current_trace->reset)
> @@ -8652,15 +8658,31 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
> return ret;
> }
>
> -/* An ioctl call with cmd 0 to the ring buffer file will wake up all waiters */
> static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> {
> struct ftrace_buffer_info *info = file->private_data;
> struct trace_iterator *iter = &info->iter;
> + int err;
> +
> + if (cmd == TRACE_MMAP_IOCTL_GET_READER) {
> + if (!(file->f_flags & O_NONBLOCK)) {
> + err = ring_buffer_wait(iter->array_buffer->buffer,
> + iter->cpu_file,
> + iter->tr->buffer_percent);
> + if (err)
> + return err;
> + }
>
> - if (cmd)
> - return -ENOIOCTLCMD;
> + return ring_buffer_map_get_reader(iter->array_buffer->buffer,
> + iter->cpu_file);
> + } else if (cmd) {
> + return -ENOTTY;
> + }
>
> + /*
> + * An ioctl call with cmd 0 to the ring buffer file will wake up all
> + * waiters
> + */
> mutex_lock(&trace_types_lock);
>
> iter->wait_index++;
> @@ -8673,6 +8695,97 @@ static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, unsigned
> return 0;
> }
>
> +static vm_fault_t tracing_buffers_mmap_fault(struct vm_fault *vmf)
> +{
> + struct ftrace_buffer_info *info = vmf->vma->vm_file->private_data;
> + struct trace_iterator *iter = &info->iter;
> + vm_fault_t ret = VM_FAULT_SIGBUS;
> + struct page *page;
> +
> + page = ring_buffer_map_fault(iter->array_buffer->buffer, iter->cpu_file,
> + vmf->pgoff);
> + if (!page)
> + return ret;
> +
> + get_page(page);
> + vmf->page = page;
> + vmf->page->mapping = vmf->vma->vm_file->f_mapping;
> + vmf->page->index = vmf->pgoff;
> +
> + return 0;
> +}
> +
> +static void tracing_buffers_mmap_close(struct vm_area_struct *vma)
> +{
> + struct ftrace_buffer_info *info = vma->vm_file->private_data;
> + struct trace_iterator *iter = &info->iter;
> + struct trace_array *tr = iter->tr;
> +
> + ring_buffer_unmap(iter->array_buffer->buffer, iter->cpu_file);
> +
> +#ifdef CONFIG_TRACER_MAX_TRACE
> + spin_lock(&tr->snapshot_trigger_lock);
> + if (!WARN_ON(!tr->mapped))
> + tr->mapped--;
> + spin_unlock(&tr->snapshot_trigger_lock);
> +#endif
> +}
> +
> +static void tracing_buffers_mmap_open(struct vm_area_struct *vma)
> +{
> + struct ftrace_buffer_info *info = vma->vm_file->private_data;
> + struct trace_iterator *iter = &info->iter;
> +
> + WARN_ON(ring_buffer_map(iter->array_buffer->buffer, iter->cpu_file));
> +}
> +
> +static const struct vm_operations_struct tracing_buffers_vmops = {
> + .open = tracing_buffers_mmap_open,
> + .close = tracing_buffers_mmap_close,
> + .fault = tracing_buffers_mmap_fault,
> +};
> +
> +static int tracing_buffers_mmap(struct file *filp, struct vm_area_struct *vma)
> +{
> + struct ftrace_buffer_info *info = filp->private_data;
> + struct trace_iterator *iter = &info->iter;
> + struct trace_array *tr = iter->tr;
> + int ret = 0;
> +
> + if (vma->vm_flags & VM_WRITE)
> + return -EPERM;
> +
> + vm_flags_mod(vma, VM_DONTCOPY | VM_DONTDUMP, VM_MAYWRITE);
> + vma->vm_ops = &tracing_buffers_vmops;
> +
> +#ifdef CONFIG_TRACER_MAX_TRACE
> + /*
> + * We hold mmap_lock here. lockdep would be unhappy if we would now take
> + * trace_types_lock. Instead use the specific snapshot_trigger_lock.
> + */
> + spin_lock(&tr->snapshot_trigger_lock);
> + if (tr->snapshot || tr->mapped == UINT_MAX) {
> + spin_unlock(&tr->snapshot_trigger_lock);
> + return -EBUSY;
> + }
> + tr->mapped++;
> + spin_unlock(&tr->snapshot_trigger_lock);
> +
> + /* Wait for update_max_tr() to observe iter->tr->mapped */
> + if (tr->mapped == 1)
> + synchronize_rcu();
> +#endif
> + ret = ring_buffer_map(iter->array_buffer->buffer, iter->cpu_file);
> +#ifdef CONFIG_TRACER_MAX_TRACE
> + if (ret) {
> + spin_lock(&tr->snapshot_trigger_lock);
> + iter->tr->mapped--;
> + spin_unlock(&tr->snapshot_trigger_lock);
> + }
> +#endif
> + return ret;
> +}
> +
> static const struct file_operations tracing_buffers_fops = {
> .open = tracing_buffers_open,
> .read = tracing_buffers_read,
> @@ -8681,6 +8794,7 @@ static const struct file_operations tracing_buffers_fops = {
> .splice_read = tracing_buffers_splice_read,
> .unlocked_ioctl = tracing_buffers_ioctl,
> .llseek = no_llseek,
> + .mmap = tracing_buffers_mmap,
> };
>
> static ssize_t
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index bd312e9afe25..8a96e7a89e6b 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -336,6 +336,7 @@ struct trace_array {
> bool allocated_snapshot;
> spinlock_t snapshot_trigger_lock;
> unsigned int snapshot;
> + unsigned int mapped;
> unsigned long max_latency;
> #ifdef CONFIG_FSNOTIFY
> struct dentry *d_max_latency;
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
On Mon, Feb 05, 2024 at 11:55:08AM -0500, Mathieu Desnoyers wrote:
> On 2024-02-05 11:34, Vincent Donnefort wrote:
> > Currently, user-space extracts data from the ring-buffer via splice,
> > which is handy for storage or network sharing. However, due to splice
> > limitations, it is imposible to do real-time analysis without a copy.
> >
> > A solution for that problem is to let the user-space map the ring-buffer
> > directly.
> >
> > The mapping is exposed via the per-CPU file trace_pipe_raw. The first
> > element of the mapping is the meta-page. It is followed by each
> > subbuffer constituting the ring-buffer, ordered by their unique page ID:
> >
> > * Meta-page -- include/uapi/linux/trace_mmap.h for a description
> > * Subbuf ID 0
> > * Subbuf ID 1
> > ...
> >
> > It is therefore easy to translate a subbuf ID into an offset in the
> > mapping:
> >
> > reader_id = meta->reader->id;
> > reader_offset = meta->meta_page_size + reader_id * meta->subbuf_size;
> >
> > When new data is available, the mapper must call a newly introduced ioctl:
> > TRACE_MMAP_IOCTL_GET_READER. This will update the Meta-page reader ID to
> > point to the next reader containing unread data.
> >
> > Mapping will prevent snapshot and buffer size modifications.
>
> How are the kernel linear mapping and the userspace mapping made coherent
> on architectures with virtually aliasing data caches ?
>
> Ref. https://lore.kernel.org/lkml/[email protected]/T/#t
Hi Mathieu,
Thanks for the pointer.
We are in the exact same problem as DAX. We do modify the data through the
kernel linear mapping while user-space can read it through its own. I should
probably return an error when used with any of the arch ARM || SPARC || MIPS,
until cpu_dcache_is_aliasing() introduces a fine-grain differentiation.
>
> Thanks,
>
> Mathieu
>
> >
> > Signed-off-by: Vincent Donnefort <[email protected]>
> >
> > diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mmap.h
> > index 182e05a3004a..7330249257e7 100644
> > --- a/include/uapi/linux/trace_mmap.h
> > +++ b/include/uapi/linux/trace_mmap.h
> > @@ -43,4 +43,6 @@ struct trace_buffer_meta {
> > __u64 Reserved2;
> > };
> > +#define TRACE_MMAP_IOCTL_GET_READER _IO('T', 0x1)
> > +
> > #endif /* _TRACE_MMAP_H_ */
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > index 4ebf4d0bd14c..36b62cf2fb3f 100644
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -1175,6 +1175,12 @@ static void tracing_snapshot_instance_cond(struct trace_array *tr,
> > return;
> > }
> > + if (tr->mapped) {
> > + trace_array_puts(tr, "*** BUFFER MEMORY MAPPED ***\n");
> > + trace_array_puts(tr, "*** Can not use snapshot (sorry) ***\n");
> > + return;
> > + }
> > +
> > local_irq_save(flags);
> > update_max_tr(tr, current, smp_processor_id(), cond_data);
> > local_irq_restore(flags);
> > @@ -1307,7 +1313,7 @@ static int tracing_arm_snapshot_locked(struct trace_array *tr)
> > lockdep_assert_held(&trace_types_lock);
> > spin_lock(&tr->snapshot_trigger_lock);
> > - if (tr->snapshot == UINT_MAX) {
> > + if (tr->snapshot == UINT_MAX || tr->mapped) {
> > spin_unlock(&tr->snapshot_trigger_lock);
> > return -EBUSY;
> > }
> > @@ -6533,7 +6539,7 @@ static void tracing_set_nop(struct trace_array *tr)
> > {
> > if (tr->current_trace == &nop_trace)
> > return;
> > -
> > +
> > tr->current_trace->enabled--;
> > if (tr->current_trace->reset)
> > @@ -8652,15 +8658,31 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
> > return ret;
> > }
> > -/* An ioctl call with cmd 0 to the ring buffer file will wake up all waiters */
> > static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> > {
> > struct ftrace_buffer_info *info = file->private_data;
> > struct trace_iterator *iter = &info->iter;
> > + int err;
> > +
> > + if (cmd == TRACE_MMAP_IOCTL_GET_READER) {
> > + if (!(file->f_flags & O_NONBLOCK)) {
> > + err = ring_buffer_wait(iter->array_buffer->buffer,
> > + iter->cpu_file,
> > + iter->tr->buffer_percent);
> > + if (err)
> > + return err;
> > + }
> > - if (cmd)
> > - return -ENOIOCTLCMD;
> > + return ring_buffer_map_get_reader(iter->array_buffer->buffer,
> > + iter->cpu_file);
> > + } else if (cmd) {
> > + return -ENOTTY;
> > + }
> > + /*
> > + * An ioctl call with cmd 0 to the ring buffer file will wake up all
> > + * waiters
> > + */
> > mutex_lock(&trace_types_lock);
> > iter->wait_index++;
> > @@ -8673,6 +8695,97 @@ static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, unsigned
> > return 0;
> > }
> > +static vm_fault_t tracing_buffers_mmap_fault(struct vm_fault *vmf)
> > +{
> > + struct ftrace_buffer_info *info = vmf->vma->vm_file->private_data;
> > + struct trace_iterator *iter = &info->iter;
> > + vm_fault_t ret = VM_FAULT_SIGBUS;
> > + struct page *page;
> > +
> > + page = ring_buffer_map_fault(iter->array_buffer->buffer, iter->cpu_file,
> > + vmf->pgoff);
> > + if (!page)
> > + return ret;
> > +
> > + get_page(page);
> > + vmf->page = page;
> > + vmf->page->mapping = vmf->vma->vm_file->f_mapping;
> > + vmf->page->index = vmf->pgoff;
> > +
> > + return 0;
> > +}
> > +
> > +static void tracing_buffers_mmap_close(struct vm_area_struct *vma)
> > +{
> > + struct ftrace_buffer_info *info = vma->vm_file->private_data;
> > + struct trace_iterator *iter = &info->iter;
> > + struct trace_array *tr = iter->tr;
> > +
> > + ring_buffer_unmap(iter->array_buffer->buffer, iter->cpu_file);
> > +
> > +#ifdef CONFIG_TRACER_MAX_TRACE
> > + spin_lock(&tr->snapshot_trigger_lock);
> > + if (!WARN_ON(!tr->mapped))
> > + tr->mapped--;
> > + spin_unlock(&tr->snapshot_trigger_lock);
> > +#endif
> > +}
> > +
> > +static void tracing_buffers_mmap_open(struct vm_area_struct *vma)
> > +{
> > + struct ftrace_buffer_info *info = vma->vm_file->private_data;
> > + struct trace_iterator *iter = &info->iter;
> > +
> > + WARN_ON(ring_buffer_map(iter->array_buffer->buffer, iter->cpu_file));
> > +}
> > +
> > +static const struct vm_operations_struct tracing_buffers_vmops = {
> > + .open = tracing_buffers_mmap_open,
> > + .close = tracing_buffers_mmap_close,
> > + .fault = tracing_buffers_mmap_fault,
> > +};
> > +
> > +static int tracing_buffers_mmap(struct file *filp, struct vm_area_struct *vma)
> > +{
> > + struct ftrace_buffer_info *info = filp->private_data;
> > + struct trace_iterator *iter = &info->iter;
> > + struct trace_array *tr = iter->tr;
> > + int ret = 0;
> > +
> > + if (vma->vm_flags & VM_WRITE)
> > + return -EPERM;
> > +
> > + vm_flags_mod(vma, VM_DONTCOPY | VM_DONTDUMP, VM_MAYWRITE);
> > + vma->vm_ops = &tracing_buffers_vmops;
> > +
> > +#ifdef CONFIG_TRACER_MAX_TRACE
> > + /*
> > + * We hold mmap_lock here. lockdep would be unhappy if we would now take
> > + * trace_types_lock. Instead use the specific snapshot_trigger_lock.
> > + */
> > + spin_lock(&tr->snapshot_trigger_lock);
> > + if (tr->snapshot || tr->mapped == UINT_MAX) {
> > + spin_unlock(&tr->snapshot_trigger_lock);
> > + return -EBUSY;
> > + }
> > + tr->mapped++;
> > + spin_unlock(&tr->snapshot_trigger_lock);
> > +
> > + /* Wait for update_max_tr() to observe iter->tr->mapped */
> > + if (tr->mapped == 1)
> > + synchronize_rcu();
> > +#endif
> > + ret = ring_buffer_map(iter->array_buffer->buffer, iter->cpu_file);
> > +#ifdef CONFIG_TRACER_MAX_TRACE
> > + if (ret) {
> > + spin_lock(&tr->snapshot_trigger_lock);
> > + iter->tr->mapped--;
> > + spin_unlock(&tr->snapshot_trigger_lock);
> > + }
> > +#endif
> > + return ret;
> > +}
> > +
> > static const struct file_operations tracing_buffers_fops = {
> > .open = tracing_buffers_open,
> > .read = tracing_buffers_read,
> > @@ -8681,6 +8794,7 @@ static const struct file_operations tracing_buffers_fops = {
> > .splice_read = tracing_buffers_splice_read,
> > .unlocked_ioctl = tracing_buffers_ioctl,
> > .llseek = no_llseek,
> > + .mmap = tracing_buffers_mmap,
> > };
> > static ssize_t
> > diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> > index bd312e9afe25..8a96e7a89e6b 100644
> > --- a/kernel/trace/trace.h
> > +++ b/kernel/trace/trace.h
> > @@ -336,6 +336,7 @@ struct trace_array {
> > bool allocated_snapshot;
> > spinlock_t snapshot_trigger_lock;
> > unsigned int snapshot;
> > + unsigned int mapped;
> > unsigned long max_latency;
> > #ifdef CONFIG_FSNOTIFY
> > struct dentry *d_max_latency;
>
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> https://www.efficios.com
>
On 2024-02-05 13:34, Vincent Donnefort wrote:
> On Mon, Feb 05, 2024 at 11:55:08AM -0500, Mathieu Desnoyers wrote:
[...]
>>
>> How are the kernel linear mapping and the userspace mapping made coherent
>> on architectures with virtually aliasing data caches ?
>>
>> Ref. https://lore.kernel.org/lkml/[email protected]/T/#t
>
> Hi Mathieu,
>
> Thanks for the pointer.
>
> We are in the exact same problem as DAX. We do modify the data through the
> kernel linear mapping while user-space can read it through its own. I should
> probably return an error when used with any of the arch ARM || SPARC || MIPS,
> until cpu_dcache_is_aliasing() introduces a fine-grain differentiation.
You might want to use LTTng's ring buffer approach instead. See
https://github.com/lttng/lttng-modules/blob/master/src/lib/ringbuffer/ring_buffer_frontend.c#L1202
lib_ring_buffer_flush_read_subbuf_dcache()
Basically, whenever user-space grabs a sub-buffer for reading (through
lttng-modules's LTTNG_KERNEL_ABI_RING_BUFFER_GET_SUBBUF ioctl), lttng
calls flush_dcache_page() on all pages of this subbuffer (I should
really change this for a call to flush_dcache_folio() which would be
more efficient).
Note that doing this is not very efficient on architectures which have
coherent data caches and incoherent dcache vs icache: in that case,
we issue the flush_dcache_page uselessly. I plan on using the new
cpu_dcache_is_aliasing() check once/if it makes it way upstream to
remove those useless flushes on architectures which define
ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE, but do not virtually alias the
data cache.
The equivalent of LTTng's "get subbuf" operation would be
the new TRACE_MMAP_IOCTL_GET_READER ioctl in ftrace AFAIU.
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
On Mon, Feb 05, 2024 at 01:44:47PM -0500, Mathieu Desnoyers wrote:
> On 2024-02-05 13:34, Vincent Donnefort wrote:
> > On Mon, Feb 05, 2024 at 11:55:08AM -0500, Mathieu Desnoyers wrote:
> [...]
>
> > >
> > > How are the kernel linear mapping and the userspace mapping made coherent
> > > on architectures with virtually aliasing data caches ?
> > >
> > > Ref. https://lore.kernel.org/lkml/[email protected]/T/#t
> >
> > Hi Mathieu,
> >
> > Thanks for the pointer.
> >
> > We are in the exact same problem as DAX. We do modify the data through the
> > kernel linear mapping while user-space can read it through its own. I should
> > probably return an error when used with any of the arch ARM || SPARC || MIPS,
> > until cpu_dcache_is_aliasing() introduces a fine-grain differentiation.
>
> You might want to use LTTng's ring buffer approach instead. See
>
> https://github.com/lttng/lttng-modules/blob/master/src/lib/ringbuffer/ring_buffer_frontend.c#L1202
>
> lib_ring_buffer_flush_read_subbuf_dcache()
Thanks!
>
> Basically, whenever user-space grabs a sub-buffer for reading (through
> lttng-modules's LTTNG_KERNEL_ABI_RING_BUFFER_GET_SUBBUF ioctl), lttng
> calls flush_dcache_page() on all pages of this subbuffer (I should
> really change this for a call to flush_dcache_folio() which would be
> more efficient).
>
> Note that doing this is not very efficient on architectures which have
> coherent data caches and incoherent dcache vs icache: in that case,
> we issue the flush_dcache_page uselessly. I plan on using the new
> cpu_dcache_is_aliasing() check once/if it makes it way upstream to
> remove those useless flushes on architectures which define
> ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE, but do not virtually alias the
> data cache.
I believe the aim is to use the mapping by default in libtracefs and fallback to
splice whenever not available... But for those arch, I guess that might be a
mistake. Wonder if then it isn't just better to return ENOTSUPP?
>
> The equivalent of LTTng's "get subbuf" operation would be
> the new TRACE_MMAP_IOCTL_GET_READER ioctl in ftrace AFAIU.
That is correct!
>
> Thanks,
>
> Mathieu
>
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> https://www.efficios.com
>
Hi Vincent,
kernel test robot noticed the following build warnings:
[auto build test WARNING on e2412e51fdea837b50ce31fea8e5dfc885237f3a]
url: https://github.com/intel-lab-lkp/linux/commits/Vincent-Donnefort/ring-buffer-Zero-ring-buffer-sub-buffers/20240206-004413
base: e2412e51fdea837b50ce31fea8e5dfc885237f3a
patch link: https://lore.kernel.org/r/20240205163410.2296552-5-vdonnefort%40google.com
patch subject: [PATCH v14 4/6] tracing: Allow user-space mapping of the ring-buffer
config: arc-defconfig (https://download.01.org/0day-ci/archive/20240206/[email protected]/config)
compiler: arc-elf-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240206/[email protected]/reproduce)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <[email protected]>
| Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
All warnings (new ones prefixed by >>):
kernel/trace/trace.c: In function 'tracing_buffers_mmap_close':
>> kernel/trace/trace.c:8722:29: warning: unused variable 'tr' [-Wunused-variable]
8722 | struct trace_array *tr = iter->tr;
| ^~
kernel/trace/trace.c: In function 'tracing_buffers_mmap':
kernel/trace/trace.c:8752:29: warning: unused variable 'tr' [-Wunused-variable]
8752 | struct trace_array *tr = iter->tr;
| ^~
vim +/tr +8722 kernel/trace/trace.c
8717
8718 static void tracing_buffers_mmap_close(struct vm_area_struct *vma)
8719 {
8720 struct ftrace_buffer_info *info = vma->vm_file->private_data;
8721 struct trace_iterator *iter = &info->iter;
> 8722 struct trace_array *tr = iter->tr;
8723
8724 ring_buffer_unmap(iter->array_buffer->buffer, iter->cpu_file);
8725
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki