Commit 6050cb0b authored Jul 23, 2013 by Frederic Weisbecker Committed by Ingo Molnar Jul 30, 2013

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@infradead.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1374539466-4799-2-git-send-email-fweisbec@gmail.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 7d9ffa89

kernel/events/core.c

+6 −6

Original line number	Diff line number	Diff line
		@@ -6567,6 +6567,12 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
		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) {
		@@ -6574,12 +6580,6 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
		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;