[PATCH 1/8] perf: Fix branch stack refcount leak on callchain init failure

[Frederic Weisbecker]

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 <peterz@xxxxxxxxxxxxx>
Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
---
 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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