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>

1 files changed, 6 insertions, 6 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 127411400116..f35aa7e69e2d 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6567,6 +6567,12 @@ 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) {
@@ -6574,12 +6580,6 @@ 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;