5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Zheng Yejian <zhengyejian1@xxxxxxxxxx>
[ Upstream commit 45d99ea451d0c30bfd4864f0fe485d7dac014902 ]
The 'bytes' info in file 'per_cpu/cpu<X>/stats' means the number of
bytes in cpu buffer that have not been consumed. However, currently
after consuming data by reading file 'trace_pipe', the 'bytes' info
was not changed as expected.
# cat per_cpu/cpu0/stats
entries: 0
overrun: 0
commit overrun: 0
bytes: 568 <--- 'bytes' is problematical !!!
oldest event ts: 8651.371479
now ts: 8653.912224
dropped events: 0
read events: 8
The root cause is incorrect stat on cpu_buffer->read_bytes. To fix it:
1. When stat 'read_bytes', account consumed event in rb_advance_reader();
2. When stat 'entries_bytes', exclude the discarded padding event which
is smaller than minimum size because it is invisible to reader. Then
use rb_page_commit() instead of BUF_PAGE_SIZE at where accounting for
page-based read/remove/overrun.
Also correct the comments of ring_buffer_bytes_cpu() in this patch.
Link: https://lore.kernel.org/linux-trace-kernel/20230921125425.1708423-1-zhengyejian1@xxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Fixes: c64e148a3be3 ("trace: Add ring buffer stats to measure rate of events")
Signed-off-by: Zheng Yejian <zhengyejian1@xxxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
kernel/trace/ring_buffer.c | 28 +++++++++++++++-------------
1 file changed, 15 insertions(+), 13 deletions(-)
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 352a7de4fc458..e5dc7b5a261c6 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -346,6 +346,11 @@ static void rb_init_page(struct buffer_data_page *bpage)
local_set(&bpage->commit, 0);
}
+static __always_inline unsigned int rb_page_commit(struct buffer_page *bpage)
+{
+ return local_read(&bpage->page->commit);
+}
+
static void free_buffer_page(struct buffer_page *bpage)
{
free_page((unsigned long)bpage->page);
@@ -1984,7 +1989,7 @@ rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned long nr_pages)
* Increment overrun to account for the lost events.
*/
local_add(page_entries, &cpu_buffer->overrun);
- local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
+ local_sub(rb_page_commit(to_remove_page), &cpu_buffer->entries_bytes);
local_inc(&cpu_buffer->pages_lost);
}
@@ -2328,11 +2333,6 @@ rb_reader_event(struct ring_buffer_per_cpu *cpu_buffer)
cpu_buffer->reader_page->read);
}
-static __always_inline unsigned rb_page_commit(struct buffer_page *bpage)
-{
- return local_read(&bpage->page->commit);
-}
-
static struct ring_buffer_event *
rb_iter_head_event(struct ring_buffer_iter *iter)
{
@@ -2478,7 +2478,7 @@ rb_handle_head_page(struct ring_buffer_per_cpu *cpu_buffer,
* the counters.
*/
local_add(entries, &cpu_buffer->overrun);
- local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
+ local_sub(rb_page_commit(next_page), &cpu_buffer->entries_bytes);
local_inc(&cpu_buffer->pages_lost);
/*
@@ -2621,9 +2621,6 @@ rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
event = __rb_page_index(tail_page, tail);
- /* account for padding bytes */
- local_add(BUF_PAGE_SIZE - tail, &cpu_buffer->entries_bytes);
-
/*
* Save the original length to the meta data.
* This will be used by the reader to add lost event
@@ -2637,7 +2634,8 @@ rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
* write counter enough to allow another writer to slip
* in on this page.
* We put in a discarded commit instead, to make sure
- * that this space is not used again.
+ * that this space is not used again, and this space will
+ * not be accounted into 'entries_bytes'.
*
* If we are less than the minimum size, we don't need to
* worry about it.
@@ -2662,6 +2660,9 @@ rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
/* time delta must be non zero */
event->time_delta = 1;
+ /* account for padding bytes */
+ local_add(BUF_PAGE_SIZE - tail, &cpu_buffer->entries_bytes);
+
/* Make sure the padding is visible before the tail_page->write update */
smp_wmb();
@@ -4177,7 +4178,7 @@ u64 ring_buffer_oldest_event_ts(struct trace_buffer *buffer, int cpu)
EXPORT_SYMBOL_GPL(ring_buffer_oldest_event_ts);
/**
- * ring_buffer_bytes_cpu - get the number of bytes consumed in a cpu buffer
+ * ring_buffer_bytes_cpu - get the number of bytes unconsumed in a cpu buffer
* @buffer: The ring buffer
* @cpu: The per CPU buffer to read from.
*/
@@ -4685,6 +4686,7 @@ static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
length = rb_event_length(event);
cpu_buffer->reader_page->read += length;
+ cpu_buffer->read_bytes += length;
}
static void rb_advance_iter(struct ring_buffer_iter *iter)
@@ -5778,7 +5780,7 @@ 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 += BUF_PAGE_SIZE;
+ cpu_buffer->read_bytes += rb_page_commit(reader);
/* swap the pages */
rb_init_page(bpage);
--
2.40.1
