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Revert "perf: Avoid the read if the count is already updated"

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This reverts commit 887e39ac47 which is
commit 8ce939a0fa194939cc1f92dbd8bc1a7806e7d40a upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I39e9126c8e78ae62d961dd9e3873d43b3b9e4498
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
This commit is contained in:
Greg Kroah-Hartman
2025-06-06 11:53:52 +00:00
parent 6de79a4718
commit 614334d6e9
3 changed files with 18 additions and 24 deletions
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8
include/linux/perf_event.h
View File

@@ -1064,13 +1064,7 @@ struct perf_output_handle {
struct perf_buffer *rb;
unsigned long wakeup;
unsigned long size;
union {
u64 flags; /* perf_output*() */
u64 aux_flags; /* perf_aux_output*() */
struct {
u64 skip_read : 1;
};
};
u64 aux_flags;
union {
void *addr;
unsigned long head;

33
kernel/events/core.c
View File

@@ -1196,12 +1196,6 @@ static void perf_assert_pmu_disabled(struct pmu *pmu)
WARN_ON_ONCE(*this_cpu_ptr(pmu->pmu_disable_count) == 0);
}
static inline void perf_pmu_read(struct perf_event *event)
{
if (event->state == PERF_EVENT_STATE_ACTIVE)
event->pmu->read(event);
}
static void get_ctx(struct perf_event_context *ctx)
{
refcount_inc(&ctx->refcount);
@@ -3489,7 +3483,8 @@ static void __perf_event_sync_stat(struct perf_event *event,
* we know the event must be on the current CPU, therefore we
* don't need to use it.
*/
perf_pmu_read(event);
if (event->state == PERF_EVENT_STATE_ACTIVE)
event->pmu->read(event);
perf_event_update_time(event);
@@ -4640,8 +4635,15 @@ static void __perf_event_read(void *info)
pmu->read(event);
for_each_sibling_event(sub, event)
perf_pmu_read(sub);
for_each_sibling_event(sub, event) {
if (sub->state == PERF_EVENT_STATE_ACTIVE) {
/*
* Use sibling's PMU rather than @event's since
* sibling could be on different (eg: software) PMU.
*/
sub->pmu->read(sub);
}
}
data->ret = pmu->commit_txn(pmu);
@@ -7393,8 +7395,9 @@ static void perf_output_read_group(struct perf_output_handle *handle,
if (read_format & PERF_FORMAT_TOTAL_TIME_RUNNING)
values[n++] = running;
if ((leader != event) && !handle->skip_read)
perf_pmu_read(leader);
if ((leader != event) &&
(leader->state == PERF_EVENT_STATE_ACTIVE))
leader->pmu->read(leader);
values[n++] = perf_event_count(leader, self);
if (read_format & PERF_FORMAT_ID)
@@ -7407,8 +7410,9 @@ static void perf_output_read_group(struct perf_output_handle *handle,
for_each_sibling_event(sub, leader) {
n = 0;
if ((sub != event) && !handle->skip_read)
perf_pmu_read(sub);
if ((sub != event) &&
(sub->state == PERF_EVENT_STATE_ACTIVE))
sub->pmu->read(sub);
values[n++] = perf_event_count(sub, self);
if (read_format & PERF_FORMAT_ID)
@@ -7467,9 +7471,6 @@ void perf_output_sample(struct perf_output_handle *handle,
{
u64 sample_type = data->type;
if (data->sample_flags & PERF_SAMPLE_READ)
handle->skip_read = 1;
perf_output_put(handle, *header);
if (sample_type & PERF_SAMPLE_IDENTIFIER)

1
kernel/events/ring_buffer.c
View File

@@ -185,7 +185,6 @@ __perf_output_begin(struct perf_output_handle *handle,
handle->rb = rb;
handle->event = event;
handle->flags = 0;
have_lost = local_read(&rb->lost);
if (unlikely(have_lost)) {