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Subject[PATCH] perf/core: Increase lost_samples count only for samples
Date
The event->lost_samples count is intended to count (lost) sample records
but it's also counted for non-sample records like PERF_RECORD_MMAP etc.
This can be a problem when a sampling event tracks those side-band
events together.

As overflow handler for user events only calls perf_output_begin_
{for,back}ward() before writing to the ring buffer, we can pass an
additional flag to indicate that it's writing a sample record.

Fixes: 119a784c8127 ("perf/core: Add a new read format to get a number of lost samples")
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
kernel/events/ring_buffer.c | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 726132039c38..5f38ee4edbdb 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -149,7 +149,7 @@ static __always_inline int
__perf_output_begin(struct perf_output_handle *handle,
struct perf_sample_data *data,
struct perf_event *event, unsigned int size,
- bool backward)
+ bool backward, bool sample)
{
struct perf_buffer *rb;
unsigned long tail, offset, head;
@@ -174,7 +174,8 @@ __perf_output_begin(struct perf_output_handle *handle,
if (unlikely(rb->paused)) {
if (rb->nr_pages) {
local_inc(&rb->lost);
- atomic64_inc(&event->lost_samples);
+ if (sample)
+ atomic64_inc(&event->lost_samples);
}
goto out;
}
@@ -256,7 +257,8 @@ __perf_output_begin(struct perf_output_handle *handle,

fail:
local_inc(&rb->lost);
- atomic64_inc(&event->lost_samples);
+ if (sample)
+ atomic64_inc(&event->lost_samples);
perf_output_put_handle(handle);
out:
rcu_read_unlock();
@@ -268,14 +270,14 @@ int perf_output_begin_forward(struct perf_output_handle *handle,
struct perf_sample_data *data,
struct perf_event *event, unsigned int size)
{
- return __perf_output_begin(handle, data, event, size, false);
+ return __perf_output_begin(handle, data, event, size, false, true);
}

int perf_output_begin_backward(struct perf_output_handle *handle,
struct perf_sample_data *data,
struct perf_event *event, unsigned int size)
{
- return __perf_output_begin(handle, data, event, size, true);
+ return __perf_output_begin(handle, data, event, size, true, true);
}

int perf_output_begin(struct perf_output_handle *handle,
@@ -284,7 +286,7 @@ int perf_output_begin(struct perf_output_handle *handle,
{

return __perf_output_begin(handle, data, event, size,
- unlikely(is_write_backward(event)));
+ unlikely(is_write_backward(event)), false);
}

unsigned int perf_output_copy(struct perf_output_handle *handle,
--
2.37.2.789.g6183377224-goog
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