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tracing ring buffer updates for v6.10:

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- Add ring_buffer memory mappings
 
   The tracing ring buffer was created based on being mostly used with the
   splice system call. It is broken up into page ordered sub-buffers and the
   reader swaps a new sub-buffer with an existing sub-buffer that's part
   of the write buffer. It then has total access to the swapped out
   sub-buffer and can do copyless movements of the memory into other mediums
   (file system, network, etc).
 
   The buffer is great for passing around the ring buffer contents in the
   kernel, but is not so good for when the consumer is the user space task
   itself.
 
   A new interface is added that allows user space to memory map the ring
   buffer. It will get all the write sub-buffers as well as reader sub-buffer
   (that is not written to). It can send an ioctl to change which sub-buffer
   is the new reader sub-buffer.
 
   The ring buffer is read only to user space. It only needs to call the
   ioctl when it is finished with a sub-buffer and needs a new sub-buffer
   that the writer will not write over.
 
   A self test program was also created for testing and can be used as
   an example for the interface to user space. The libtracefs (external
   to the kernel) also has code that interacts with this, although it is
   disabled until the interface is in a official release. It can be enabled
   by compiling the library with a special flag. This was used for testing
   applications that perform better with the buffer being mapped.
 
   Memory mapped buffers have limitations. The main one is that it can not be
   used with the snapshot logic. If the buffer is mapped, snapshots will be
   disabled. If any logic is set to trigger snapshots on a buffer, that
   buffer will not be allowed to be mapped.
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Merge tag 'trace-ringbuffer-v6.10' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull tracing ring buffer updates from Steven Rostedt:
 "Add ring_buffer memory mappings.

  The tracing ring buffer was created based on being mostly used with
  the splice system call. It is broken up into page ordered sub-buffers
  and the reader swaps a new sub-buffer with an existing sub-buffer
  that's part of the write buffer. It then has total access to the
  swapped out sub-buffer and can do copyless movements of the memory
  into other mediums (file system, network, etc).

  The buffer is great for passing around the ring buffer contents in the
  kernel, but is not so good for when the consumer is the user space
  task itself.

  A new interface is added that allows user space to memory map the ring
  buffer. It will get all the write sub-buffers as well as reader
  sub-buffer (that is not written to). It can send an ioctl to change
  which sub-buffer is the new reader sub-buffer.

  The ring buffer is read only to user space. It only needs to call the
  ioctl when it is finished with a sub-buffer and needs a new sub-buffer
  that the writer will not write over.

  A self test program was also created for testing and can be used as an
  example for the interface to user space. The libtracefs (external to
  the kernel) also has code that interacts with this, although it is
  disabled until the interface is in a official release. It can be
  enabled by compiling the library with a special flag. This was used
  for testing applications that perform better with the buffer being
  mapped.

  Memory mapped buffers have limitations. The main one is that it can
  not be used with the snapshot logic. If the buffer is mapped,
  snapshots will be disabled. If any logic is set to trigger snapshots
  on a buffer, that buffer will not be allowed to be mapped"

* tag 'trace-ringbuffer-v6.10' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ring-buffer: Add cast to unsigned long addr passed to virt_to_page()
  ring-buffer: Have mmapped ring buffer keep track of missed events
  ring-buffer/selftest: Add ring-buffer mapping test
  Documentation: tracing: Add ring-buffer mapping
  tracing: Allow user-space mapping of the ring-buffer
  ring-buffer: Introducing ring-buffer mapping functions
  ring-buffer: Allocate sub-buffers with __GFP_COMP
This commit is contained in:
Linus Torvalds 2024-05-17 18:40:37 -07:00
commit 53683e4080
11 changed files with 1026 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
Documentation/trace/index.rst
View File

@ -29,6 +29,7 @@ Linux Tracing Technologies
timerlat-tracer
intel_th
ring-buffer-design
ring-buffer-map
stm
sys-t
coresight/index

106
Documentation/trace/ring-buffer-map.rst Normal file
View File

@ -0,0 +1,106 @@
.. SPDX-License-Identifier: GPL-2.0
==================================
Tracefs ring-buffer memory mapping
==================================
:Author: Vincent Donnefort <vdonnefort@google.com>
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 to as the meta-page. One of the most important
fields 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 ascending 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 and causes splice to copy
the ring buffer data instead of using the copyless swap from the ring buffer.
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, just like concurrent readers on
trace_pipe would be.
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;
}

6
include/linux/ring_buffer.h
View File

@ -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;
@ -223,4 +225,8 @@ 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,
struct vm_area_struct *vma);
int ring_buffer_unmap(struct trace_buffer *buffer, int cpu);
int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu);
#endif /* _LINUX_RING_BUFFER_H */

48
include/uapi/linux/trace_mmap.h Normal file
View File

@ -0,0 +1,48 @@
/* 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, including the reader.
* @reader.lost_events: Number of events lost at the time of the reader swap.
* @reader.id: subbuf ID of the current reader. ID range [0 : @nr_subbufs - 1]
* @reader.read: Number of bytes read on the reader subbuf.
* @flags: Placeholder for now, 0 until new features are supported.
* @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: Internal use only.
* @Reserved2: Internal use only.
*/
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;
};
#define TRACE_MMAP_IOCTL_GET_READER _IO('T', 0x1)
#endif /* _TRACE_MMAP_H_ */

471
kernel/trace/ring_buffer.c
View File

@ -9,6 +9,7 @@
#include <linux/ring_buffer.h>
#include <linux/trace_clock.h>
#include <linux/sched/clock.h>
#include <linux/cacheflush.h>
#include <linux/trace_seq.h>
#include <linux/spinlock.h>
#include <linux/irq_work.h>
@ -26,6 +27,7 @@
#include <linux/list.h>
#include <linux/cpu.h>
#include <linux/oom.h>
#include <linux/mm.h>
#include <asm/local64.h>
#include <asm/local.h>
@ -312,6 +314,8 @@ static u64 rb_event_time_stamp(struct ring_buffer_event *event)
/* Missed count stored at end */
#define RB_MISSED_STORED (1 << 30)
#define RB_MISSED_MASK (3 << 30)
struct buffer_data_page {
u64 time_stamp; /* page time stamp */
local_t commit; /* write committed index */
@ -338,6 +342,7 @@ 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 +489,12 @@ 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 subbuf VA */
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 */
@ -1524,7 +1535,7 @@ 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 | __GFP_ZERO,
mflags | __GFP_COMP | __GFP_ZERO,
cpu_buffer->buffer->subbuf_order);
if (!page)
goto free_pages;
@ -1599,6 +1610,7 @@ 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));
@ -1609,7 +1621,7 @@ 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 | __GFP_ZERO,
page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL | __GFP_COMP | __GFP_ZERO,
cpu_buffer->buffer->subbuf_order);
if (!page)
goto fail_free_reader;
@ -1789,8 +1801,6 @@ 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;
@ -2318,7 +2328,7 @@ rb_iter_head_event(struct ring_buffer_iter *iter)
/* Size is determined by what has been committed */
static __always_inline unsigned rb_page_size(struct buffer_page *bpage)
{
return rb_page_commit(bpage);
return rb_page_commit(bpage) & ~RB_MISSED_MASK;
}
static __always_inline unsigned
@ -3945,7 +3955,7 @@ static bool rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
return true;
/* Reader should exhaust content in reader page */
if (reader->read != rb_page_commit(reader))
if (reader->read != rb_page_size(reader))
return false;
/*
@ -4416,7 +4426,7 @@ int ring_buffer_iter_empty(struct ring_buffer_iter *iter)
return ((iter->head_page == commit_page && iter->head >= commit) ||
(iter->head_page == reader && commit_page == head_page &&
head_page->read == commit &&
iter->head == rb_page_commit(cpu_buffer->reader_page)));
iter->head == rb_page_size(cpu_buffer->reader_page)));
}
EXPORT_SYMBOL_GPL(ring_buffer_iter_empty);
@ -5211,6 +5221,22 @@ 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;
meta->reader.read = cpu_buffer->reader_page->read;
meta->reader.id = cpu_buffer->reader_page->id;
meta->reader.lost_events = cpu_buffer->lost_events;
meta->entries = local_read(&cpu_buffer->entries);
meta->overrun = local_read(&cpu_buffer->overrun);
meta->read = cpu_buffer->read;
/* Some archs do not have data cache coherency between kernel and user-space */
flush_dcache_folio(virt_to_folio(cpu_buffer->meta_page));
}
static void
rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
{
@ -5255,6 +5281,9 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
cpu_buffer->lost_events = 0;
cpu_buffer->last_overrun = 0;
if (cpu_buffer->mapped)
rb_update_meta_page(cpu_buffer);
rb_head_page_activate(cpu_buffer);
cpu_buffer->pages_removed = 0;
}
@ -5469,6 +5498,12 @@ 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;
@ -5579,7 +5614,7 @@ ring_buffer_alloc_read_page(struct trace_buffer *buffer, int cpu)
goto out;
page = alloc_pages_node(cpu_to_node(cpu),
GFP_KERNEL | __GFP_NORETRY | __GFP_ZERO,
GFP_KERNEL | __GFP_NORETRY | __GFP_COMP | __GFP_ZERO,
cpu_buffer->buffer->subbuf_order);
if (!page) {
kfree(bpage);
@ -5720,7 +5755,7 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
event = rb_reader_event(cpu_buffer);
read = reader->read;
commit = rb_page_commit(reader);
commit = rb_page_size(reader);
/* Check if any events were dropped */
missed_events = cpu_buffer->lost_events;
@ -5733,7 +5768,8 @@ 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 ||
cpu_buffer->mapped) {
struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
unsigned int rpos = read;
unsigned int pos = 0;
@ -5796,7 +5832,7 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
} else {
/* update the entry counter */
cpu_buffer->read += rb_page_entries(reader);
cpu_buffer->read_bytes += rb_page_commit(reader);
cpu_buffer->read_bytes += rb_page_size(reader);
/* swap the pages */
rb_init_page(bpage);
@ -5956,6 +5992,11 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
cpu_buffer = buffer->buffers[cpu];
if (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);
@ -6057,6 +6098,414 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
}
EXPORT_SYMBOL_GPL(ring_buffer_subbuf_order_set);
static int rb_alloc_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
{
struct page *page;
if (cpu_buffer->meta_page)
return 0;
page = alloc_page(GFP_USER | __GFP_ZERO);
if (!page)
return -ENOMEM;
cpu_buffer->meta_page = page_to_virt(page);
return 0;
}
static void rb_free_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
{
unsigned long addr = (unsigned long)cpu_buffer->meta_page;
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;
cpu_buffer->reader_page->id = id++;
first_subbuf = subbuf = rb_set_head_page(cpu_buffer);
do {
if (WARN_ON(id >= nr_subbufs))
break;
subbuf_ids[id] = (unsigned long)subbuf->page;
subbuf->id = id;
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 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 void rb_put_mapped_buffer(struct ring_buffer_per_cpu *cpu_buffer)
{
mutex_unlock(&cpu_buffer->mapping_lock);
}
/*
* Fast-path for rb_buffer_(un)map(). Called whenever the meta-page doesn't need
* to be set-up or torn-down.
*/
static int __rb_inc_dec_mapped(struct ring_buffer_per_cpu *cpu_buffer,
bool inc)
{
unsigned long flags;
lockdep_assert_held(&cpu_buffer->mapping_lock);
if (inc && cpu_buffer->mapped == UINT_MAX)
return -EBUSY;
if (WARN_ON(!inc && cpu_buffer->mapped == 0))
return -EINVAL;
mutex_lock(&cpu_buffer->buffer->mutex);
raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
if (inc)
cpu_buffer->mapped++;
else
cpu_buffer->mapped--;
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
mutex_unlock(&cpu_buffer->buffer->mutex);
return 0;
}
/*
* +--------------+ pgoff == 0
* | meta page |
* +--------------+ pgoff == 1
* | subbuffer 0 |
* | |
* +--------------+ pgoff == (1 + (1 << subbuf_order))
* | subbuffer 1 |
* | |
* ...
*/
#ifdef CONFIG_MMU
static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer,
struct vm_area_struct *vma)
{
unsigned long nr_subbufs, nr_pages, vma_pages, pgoff = vma->vm_pgoff;
unsigned int subbuf_pages, subbuf_order;
struct page **pages;
int p = 0, s = 0;
int err;
/* Refuse MP_PRIVATE or writable mappings */
if (vma->vm_flags & VM_WRITE || vma->vm_flags & VM_EXEC ||
!(vma->vm_flags & VM_MAYSHARE))
return -EPERM;
/*
* Make sure the mapping cannot become writable later. Also tell the VM
* to not touch these pages (VM_DONTCOPY | VM_DONTEXPAND).
*/
vm_flags_mod(vma, VM_DONTCOPY | VM_DONTEXPAND | VM_DONTDUMP,
VM_MAYWRITE);
lockdep_assert_held(&cpu_buffer->mapping_lock);
subbuf_order = cpu_buffer->buffer->subbuf_order;
subbuf_pages = 1 << subbuf_order;
nr_subbufs = cpu_buffer->nr_pages + 1; /* + reader-subbuf */
nr_pages = ((nr_subbufs) << subbuf_order) - pgoff + 1; /* + meta-page */
vma_pages = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
if (!vma_pages || vma_pages > nr_pages)
return -EINVAL;
nr_pages = vma_pages;
pages = kcalloc(nr_pages, sizeof(*pages), GFP_KERNEL);
if (!pages)
return -ENOMEM;
if (!pgoff) {
pages[p++] = virt_to_page(cpu_buffer->meta_page);
/*
* TODO: Align sub-buffers on their size, once
* vm_insert_pages() supports the zero-page.
*/
} else {
/* Skip the meta-page */
pgoff--;
if (pgoff % subbuf_pages) {
err = -EINVAL;
goto out;
}
s += pgoff / subbuf_pages;
}
while (p < nr_pages) {
struct page *page = virt_to_page((void *)cpu_buffer->subbuf_ids[s]);
int off = 0;
if (WARN_ON_ONCE(s >= nr_subbufs)) {
err = -EINVAL;
goto out;
}
for (; off < (1 << (subbuf_order)); off++, page++) {
if (p >= nr_pages)
break;
pages[p++] = page;
}
s++;
}
err = vm_insert_pages(vma, vma->vm_start, pages, &nr_pages);
out:
kfree(pages);
return err;
}
#else
static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer,
struct vm_area_struct *vma)
{
return -EOPNOTSUPP;
}
#endif
int ring_buffer_map(struct trace_buffer *buffer, int cpu,
struct vm_area_struct *vma)
{
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) {
err = __rb_map_vma(cpu_buffer, vma);
if (!err)
err = __rb_inc_dec_mapped(cpu_buffer, true);
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 = kcalloc(cpu_buffer->nr_pages + 1, sizeof(*subbuf_ids), 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);
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
err = __rb_map_vma(cpu_buffer, vma);
if (!err) {
raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
cpu_buffer->mapped = 1;
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
} else {
kfree(cpu_buffer->subbuf_ids);
cpu_buffer->subbuf_ids = NULL;
rb_free_meta_page(cpu_buffer);
}
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) {
__rb_inc_dec_mapped(cpu_buffer, false);
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);
kfree(cpu_buffer->subbuf_ids);
cpu_buffer->subbuf_ids = NULL;
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;
}
int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct buffer_page *reader;
unsigned long missed_events;
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;
}
reader = rb_get_reader_page(cpu_buffer);
if (WARN_ON(!reader))
goto out;
/* Check if any events were dropped */
missed_events = cpu_buffer->lost_events;
if (cpu_buffer->reader_page != cpu_buffer->commit_page) {
if (missed_events) {
struct buffer_data_page *bpage = reader->page;
unsigned int commit;
/*
* Use the real_end for the data size,
* This gives us a chance to store the lost events
* on the page.
*/
if (reader->real_end)
local_set(&bpage->commit, reader->real_end);
/*
* If there is room at the end of the page to save the
* missed events, then record it there.
*/
commit = rb_page_size(reader);
if (buffer->subbuf_size - commit >= sizeof(missed_events)) {
memcpy(&bpage->data[commit], &missed_events,
sizeof(missed_events));
local_add(RB_MISSED_STORED, &bpage->commit);
}
local_add(RB_MISSED_EVENTS, &bpage->commit);
}
} else {
/*
* There really shouldn't be any missed events if the commit
* is on the reader page.
*/
WARN_ON_ONCE(missed_events);
}
cpu_buffer->lost_events = 0;
goto consume;
out:
/* Some archs do not have data cache coherency between kernel and user-space */
flush_dcache_folio(virt_to_folio(cpu_buffer->reader_page->page));
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

104
kernel/trace/trace.c
View File

@ -1191,6 +1191,12 @@ 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);
@ -1323,7 +1329,7 @@ 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;
}
@ -6068,7 +6074,7 @@ 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)
@ -8194,15 +8200,32 @@ 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)
return -ENOIOCTLCMD;
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,
NULL, NULL);
if (err)
return err;
}
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);
/* Make sure the waiters see the new wait_index */
@ -8214,6 +8237,76 @@ static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, unsigned
return 0;
}
#ifdef CONFIG_TRACER_MAX_TRACE
static int get_snapshot_map(struct trace_array *tr)
{
int err = 0;
/*
* Called with mmap_lock held. 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)
err = -EBUSY;
else
tr->mapped++;
spin_unlock(&tr->snapshot_trigger_lock);
/* Wait for update_max_tr() to observe iter->tr->mapped */
if (tr->mapped == 1)
synchronize_rcu();
return err;
}
static void put_snapshot_map(struct trace_array *tr)
{
spin_lock(&tr->snapshot_trigger_lock);
if (!WARN_ON(!tr->mapped))
tr->mapped--;
spin_unlock(&tr->snapshot_trigger_lock);
}
#else
static inline int get_snapshot_map(struct trace_array *tr) { return 0; }
static inline void put_snapshot_map(struct trace_array *tr) { }
#endif
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;
WARN_ON(ring_buffer_unmap(iter->array_buffer->buffer, iter->cpu_file));
put_snapshot_map(iter->tr);
}
static const struct vm_operations_struct tracing_buffers_vmops = {
.close = tracing_buffers_mmap_close,
};
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;
int ret = 0;
ret = get_snapshot_map(iter->tr);
if (ret)
return ret;
ret = ring_buffer_map(iter->array_buffer->buffer, iter->cpu_file, vma);
if (ret)
put_snapshot_map(iter->tr);
vma->vm_ops = &tracing_buffers_vmops;
return ret;
}
static const struct file_operations tracing_buffers_fops = {
.open = tracing_buffers_open,
.read = tracing_buffers_read,
@ -8223,6 +8316,7 @@ 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

1
kernel/trace/trace.h
View File

@ -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;

1
tools/testing/selftests/ring-buffer/.gitignore vendored Normal file
View File

@ -0,0 +1 @@
map_test

8
tools/testing/selftests/ring-buffer/Makefile Normal file
View File

@ -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

2
tools/testing/selftests/ring-buffer/config Normal file
View File

@ -0,0 +1,2 @@
CONFIG_FTRACE=y
CONFIG_TRACER_SNAPSHOT=y

294
tools/testing/selftests/ring-buffer/map_test.c Normal file
View File

@ -0,0 +1,294 @@
// SPDX-License-Identifier: GPL-2.0
/*
* Ring-buffer memory mapping tests
*
* Copyright (c) 2024 Vincent Donnefort <vdonnefort@google.com>
*/
#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;
int cpu_fd;
};
int tracefs_cpu_map(struct tracefs_cpu_map_desc *desc, int cpu)
{
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;
return 0;
}
void tracefs_cpu_unmap(struct tracefs_cpu_map_desc *desc)
{
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 (getuid() != 0)
SKIP(return, "Skipping: %s", "Please run the test as root");
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;
}
TEST_F(map, data_mmap)
{
struct tracefs_cpu_map_desc *desc = &self->map_desc;
unsigned long meta_len, data_len;
void *data;
meta_len = desc->meta->meta_page_size;
data_len = desc->meta->subbuf_size * desc->meta->nr_subbufs;
/* Map all the available subbufs */
data = mmap(NULL, data_len, PROT_READ, MAP_SHARED,
desc->cpu_fd, meta_len);
ASSERT_NE(data, MAP_FAILED);
munmap(data, data_len);
/* Map all the available subbufs - 1 */
data_len -= desc->meta->subbuf_size;
data = mmap(NULL, data_len, PROT_READ, MAP_SHARED,
desc->cpu_fd, meta_len);
ASSERT_NE(data, MAP_FAILED);
munmap(data, data_len);
/* Overflow the available subbufs by 1 */
meta_len += desc->meta->subbuf_size * 2;
data = mmap(NULL, data_len, PROT_READ, MAP_SHARED,
desc->cpu_fd, meta_len);
ASSERT_EQ(data, MAP_FAILED);
}
FIXTURE(snapshot) {
bool umount;
};
FIXTURE_SETUP(snapshot)
{
bool fail, umount;
struct stat sb;
char *message;
if (getuid() != 0)
SKIP(return, "Skipping: %s", "Please run the test as root");
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