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

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Message-Id: <1374539466-4799-2-git-send-email-fweisbec@gmail.com>
Date:	Tue, 23 Jul 2013 02:30:59 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Stephane Eranian <eranian@...gle.com>
Subject: [PATCH 1/8] perf: Fix branch stack refcount leak on callchain init failure

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@...radead.org>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Stephane Eranian <eranian@...gle.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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