* [for-next][PATCH 1/6] ring-buffer: Allocate sub-buffers with __GFP_COMP
2024-05-14 16:15 [for-next][PATCH 0/6] ring-buffer: Memmory mapping the ring buffer to user space Steven Rostedt
@ 2024-05-14 16:15 ` Steven Rostedt
2024-05-14 16:16 ` [for-next][PATCH 2/6] ring-buffer: Introducing ring-buffer mapping functions Steven Rostedt
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: Steven Rostedt @ 2024-05-14 16:15 UTC (permalink / raw)
To: linux-kernel
Cc: Masami Hiramatsu, Mark Rutland, Mathieu Desnoyers, Andrew Morton,
David Hildenbrand, Vincent Donnefort
From: Vincent Donnefort <vdonnefort@google.com>
In preparation for the ring-buffer memory mapping, allocate compound
pages for the ring-buffer sub-buffers to enable us to map them to
user-space with vm_insert_pages().
Link: https://lore.kernel.org/linux-trace-kernel/20240510140435.3550353-2-vdonnefort@google.com
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
kernel/trace/ring_buffer.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 6511dc3a00da..a1e011733f6a 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1524,7 +1524,7 @@ 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;
@@ -1609,7 +1609,7 @@ 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;
@@ -5579,7 +5579,7 @@ 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);
--
2.43.0
^ permalink raw reply related [flat|nested] 7+ messages in thread* [for-next][PATCH 2/6] ring-buffer: Introducing ring-buffer mapping functions
2024-05-14 16:15 [for-next][PATCH 0/6] ring-buffer: Memmory mapping the ring buffer to user space Steven Rostedt
2024-05-14 16:15 ` [for-next][PATCH 1/6] ring-buffer: Allocate sub-buffers with __GFP_COMP Steven Rostedt
@ 2024-05-14 16:16 ` Steven Rostedt
2024-05-14 16:16 ` [for-next][PATCH 3/6] tracing: Allow user-space mapping of the ring-buffer Steven Rostedt
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: Steven Rostedt @ 2024-05-14 16:16 UTC (permalink / raw)
To: linux-kernel
Cc: Masami Hiramatsu, Mark Rutland, Mathieu Desnoyers, Andrew Morton,
linux-mm, Vincent Donnefort, David Hildenbrand
From: Vincent Donnefort <vdonnefort@google.com>
In preparation for allowing the user-space to map a ring-buffer, add
a set of mapping functions:
ring_buffer_{map,unmap}()
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.
Link: https://lore.kernel.org/linux-trace-kernel/20240510140435.3550353-3-vdonnefort@google.com
CC: <linux-mm@kvack.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
include/linux/ring_buffer.h | 6 +
include/uapi/linux/trace_mmap.h | 46 ++++
kernel/trace/ring_buffer.c | 414 +++++++++++++++++++++++++++++++-
3 files changed, 463 insertions(+), 3 deletions(-)
create mode 100644 include/uapi/linux/trace_mmap.h
diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index dc5ae4e96aee..96d2140b471e 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;
@@ -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 */
diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mmap.h
new file mode 100644
index 000000000000..b682e9925539
--- /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, 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;
+};
+
+#endif /* _TRACE_MMAP_H_ */
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index a1e011733f6a..cb303052bff2 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -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>
@@ -338,6 +340,7 @@ 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 +487,12 @@ 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 */
@@ -1599,6 +1608,7 @@ 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));
@@ -1789,8 +1799,6 @@ 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;
@@ -5211,6 +5219,22 @@ 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 +5279,9 @@ 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 +5496,12 @@ 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;
@@ -5733,7 +5766,8 @@ 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;
@@ -5956,6 +5990,11 @@ 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 +6096,375 @@ 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(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;
+ 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:
+ /* 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
--
2.43.0
^ permalink raw reply related [flat|nested] 7+ messages in thread* [for-next][PATCH 3/6] tracing: Allow user-space mapping of the ring-buffer
2024-05-14 16:15 [for-next][PATCH 0/6] ring-buffer: Memmory mapping the ring buffer to user space Steven Rostedt
2024-05-14 16:15 ` [for-next][PATCH 1/6] ring-buffer: Allocate sub-buffers with __GFP_COMP Steven Rostedt
2024-05-14 16:16 ` [for-next][PATCH 2/6] ring-buffer: Introducing ring-buffer mapping functions Steven Rostedt
@ 2024-05-14 16:16 ` Steven Rostedt
2024-05-14 16:16 ` [for-next][PATCH 4/6] Documentation: tracing: Add ring-buffer mapping Steven Rostedt
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: Steven Rostedt @ 2024-05-14 16:16 UTC (permalink / raw)
To: linux-kernel
Cc: Masami Hiramatsu, Mark Rutland, Mathieu Desnoyers, Andrew Morton,
linux-mm, Vincent Donnefort
From: Vincent Donnefort <vdonnefort@google.com>
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.
Link: https://lore.kernel.org/linux-trace-kernel/20240510140435.3550353-4-vdonnefort@google.com
CC: <linux-mm@kvack.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
include/uapi/linux/trace_mmap.h | 2 +
kernel/trace/trace.c | 104 ++++++++++++++++++++++++++++++--
kernel/trace/trace.h | 1 +
3 files changed, 102 insertions(+), 5 deletions(-)
diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mmap.h
index b682e9925539..bd1066754220 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 233d1af39fff..a35e7f598233 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -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 == 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;
+ }
- 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);
/* 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
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 64450615ca0c..749a182dab48 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
^ permalink raw reply related [flat|nested] 7+ messages in thread* [for-next][PATCH 4/6] Documentation: tracing: Add ring-buffer mapping
2024-05-14 16:15 [for-next][PATCH 0/6] ring-buffer: Memmory mapping the ring buffer to user space Steven Rostedt
` (2 preceding siblings ...)
2024-05-14 16:16 ` [for-next][PATCH 3/6] tracing: Allow user-space mapping of the ring-buffer Steven Rostedt
@ 2024-05-14 16:16 ` Steven Rostedt
2024-05-14 16:16 ` [for-next][PATCH 5/6] ring-buffer/selftest: Add ring-buffer mapping test Steven Rostedt
2024-05-14 16:16 ` [for-next][PATCH 6/6] ring-buffer: Have mmapped ring buffer keep track of missed events Steven Rostedt
5 siblings, 0 replies; 7+ messages in thread
From: Steven Rostedt @ 2024-05-14 16:16 UTC (permalink / raw)
To: linux-kernel
Cc: Masami Hiramatsu, Mark Rutland, Mathieu Desnoyers, Andrew Morton,
Vincent Donnefort
From: Vincent Donnefort <vdonnefort@google.com>
It is now possible to mmap() a ring-buffer to stream its content. Add
some documentation and a code example.
Link: https://lore.kernel.org/linux-trace-kernel/20240510140435.3550353-5-vdonnefort@google.com
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
Documentation/trace/index.rst | 1 +
Documentation/trace/ring-buffer-map.rst | 106 ++++++++++++++++++++++++
2 files changed, 107 insertions(+)
create mode 100644 Documentation/trace/ring-buffer-map.rst
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..8e296bcc0d7f
--- /dev/null
+++ b/Documentation/trace/ring-buffer-map.rst
@@ -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;
+ }
--
2.43.0
^ permalink raw reply related [flat|nested] 7+ messages in thread* [for-next][PATCH 5/6] ring-buffer/selftest: Add ring-buffer mapping test
2024-05-14 16:15 [for-next][PATCH 0/6] ring-buffer: Memmory mapping the ring buffer to user space Steven Rostedt
` (3 preceding siblings ...)
2024-05-14 16:16 ` [for-next][PATCH 4/6] Documentation: tracing: Add ring-buffer mapping Steven Rostedt
@ 2024-05-14 16:16 ` Steven Rostedt
2024-05-14 16:16 ` [for-next][PATCH 6/6] ring-buffer: Have mmapped ring buffer keep track of missed events Steven Rostedt
5 siblings, 0 replies; 7+ messages in thread
From: Steven Rostedt @ 2024-05-14 16:16 UTC (permalink / raw)
To: linux-kernel
Cc: Masami Hiramatsu, Mark Rutland, Mathieu Desnoyers, Andrew Morton,
Shuah Khan, Shuah Khan, linux-kselftest, Muhammad Usama Anjum,
Vincent Donnefort
From: Vincent Donnefort <vdonnefort@google.com>
Map a ring-buffer, validate the meta-page before and after emitting few
events. Also check ring-buffer mapping boundaries and finally ensure the
tracing snapshot is mutually exclusive.
Link: https://lore.kernel.org/linux-trace-kernel/20240510140435.3550353-6-vdonnefort@google.com
Cc: Shuah Khan <shuah@kernel.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: linux-kselftest@vger.kernel.org
Acked-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
.../testing/selftests/ring-buffer/.gitignore | 1 +
tools/testing/selftests/ring-buffer/Makefile | 8 +
tools/testing/selftests/ring-buffer/config | 2 +
.../testing/selftests/ring-buffer/map_test.c | 294 ++++++++++++++++++
4 files changed, 305 insertions(+)
create mode 100644 tools/testing/selftests/ring-buffer/.gitignore
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
diff --git a/tools/testing/selftests/ring-buffer/.gitignore b/tools/testing/selftests/ring-buffer/.gitignore
new file mode 100644
index 000000000000..3aed1a2a6c67
--- /dev/null
+++ b/tools/testing/selftests/ring-buffer/.gitignore
@@ -0,0 +1 @@
+map_test
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..a9006fa7097e
--- /dev/null
+++ b/tools/testing/selftests/ring-buffer/map_test.c
@@ -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
--
2.43.0
^ permalink raw reply related [flat|nested] 7+ messages in thread* [for-next][PATCH 6/6] ring-buffer: Have mmapped ring buffer keep track of missed events
2024-05-14 16:15 [for-next][PATCH 0/6] ring-buffer: Memmory mapping the ring buffer to user space Steven Rostedt
` (4 preceding siblings ...)
2024-05-14 16:16 ` [for-next][PATCH 5/6] ring-buffer/selftest: Add ring-buffer mapping test Steven Rostedt
@ 2024-05-14 16:16 ` Steven Rostedt
5 siblings, 0 replies; 7+ messages in thread
From: Steven Rostedt @ 2024-05-14 16:16 UTC (permalink / raw)
To: linux-kernel
Cc: Masami Hiramatsu, Mark Rutland, Mathieu Desnoyers, Andrew Morton,
Vincent Donnefort
From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
While testing libtracefs on the mmapped ring buffer, the test that checks
if missed events are accounted for failed when using the mapped buffer.
This is because the mapped page does not update the missed events that
were dropped because the writer filled up the ring buffer before the
reader could catch it.
Add the missed events to the reader page/sub-buffer when the IOCTL is done
and a new reader page is acquired.
Note that all accesses to the reader_page via rb_page_commit() had to be
switched to rb_page_size(), and rb_page_size() which was just a copy of
rb_page_commit() but now it masks out the RB_MISSED bits. This is needed
as the mapped reader page is still active in the ring buffer code and
where it reads the commit field of the bpage for the size, it now must
mask it otherwise the missed bits that are now set will corrupt the size
returned.
Link: https://lore.kernel.org/linux-trace-kernel/20240312175405.12fb6726@gandalf.local.home
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
kernel/trace/ring_buffer.c | 53 +++++++++++++++++++++++++++++++++-----
1 file changed, 47 insertions(+), 6 deletions(-)
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index cb303052bff2..a02c7a52a0f5 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -314,6 +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 */
@@ -2326,7 +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
@@ -3953,7 +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;
/*
@@ -4424,7 +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);
@@ -5753,7 +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;
@@ -5830,7 +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);
@@ -6422,6 +6424,8 @@ int ring_buffer_unmap(struct trace_buffer *buffer, int cpu)
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;
@@ -6448,9 +6452,46 @@ int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu)
goto out;
}
- if (WARN_ON(!rb_get_reader_page(cpu_buffer)))
+ 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:
--
2.43.0
^ permalink raw reply related [flat|nested] 7+ messages in thread