On callchain buffers allocation failure, free_event() is
called and all the accounting performed in perf_event_alloc()
for that event is cancelled.
But if the event has branch stack sampling, it is unaccounted
as well from the branch stack sampling events refcounts.
This is a bug because this accounting is performed after the
callchain buffer allocation. As a result, the branch stack sampling
events refcount can become negative.
To fix this, move the branch stack event accounting before the
callchain buffer allocation.
Reported-by: Peter Zijlstra <pet...@infradead.org>
Signed-off-by: Frederic Weisbecker <fweis...@gmail.com>
Cc: Jiri Olsa <jo...@redhat.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Namhyung Kim <namhy...@kernel.org>
Cc: Ingo Molnar <mi...@kernel.org>
Cc: Arnaldo Carvalho de Melo <a...@redhat.com>
Cc: Stephane Eranian <eran...@google.com>
---
kernel/events/core.c | 12 ++++++------
1 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 5e2bce9..7ffb81e 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6566,6 +6566,12 @@ done:
atomic_inc(&nr_comm_events);
if (event->attr.task)
atomic_inc(&nr_task_events);
+ if (has_branch_stack(event)) {
+ static_key_slow_inc(&perf_sched_events.key);
+ if (!(event->attach_state & PERF_ATTACH_TASK))
+ atomic_inc(&per_cpu(perf_branch_stack_events,
+ event->cpu));
+ }
if (event->attr.sample_type & PERF_SAMPLE_CALLCHAIN) {
err = get_callchain_buffers();
if (err) {
@@ -6573,12 +6579,6 @@ done:
return ERR_PTR(err);
}
}
- if (has_branch_stack(event)) {
- static_key_slow_inc(&perf_sched_events.key);
- if (!(event->attach_state & PERF_ATTACH_TASK))
- atomic_inc(&per_cpu(perf_branch_stack_events,
- event->cpu));
- }
}
return event;
--
1.7.5.4
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