perf ordered_events: Fix crash in ordered_events__free

Song Liu reported crash in 'perf record':

  > #0  0x0000000000500055 in ordered_events(float, long double,...)(...) ()
  > rib#1  0x0000000000500196 in ordered_events.reinit ()
  > rib#2  0x00000000004fe413 in perf_session.process_events ()
  > rib#3  0x0000000000440431 in cmd_record ()
  > rib#4  0x00000000004a439f in run_builtin ()
  > rib#5  0x000000000042b3e5 in main ()"

This can happen when we get out of buffers during event processing.

The subsequent ordered_events__free() call assumes oe->buffer != NULL
and crashes. Add a check to prevent that.

Reported-by: Song Liu <[email protected]>
Signed-off-by: Jiri Olsa <[email protected]>
Reviewed-by: Song Liu <[email protected]>
Tested-by: Song Liu <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Fixes: d5ceb62 ("perf ordered_events: Add 'struct ordered_events_buffer' layer")
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

tools/perf/util/ordered-events.c

@@ -391,8 +391,10 @@ void ordered_events__free(struct ordered_events *oe)
 	 * Current buffer might not have all the events allocated
 	 * yet, we need to free only allocated ones ...
 	 */
-	list_del(&oe->buffer->list);
-	ordered_events_buffer__free(oe->buffer, oe->buffer_idx, oe);
+	if (oe->buffer) {
+		list_del(&oe->buffer->list);
+		ordered_events_buffer__free(oe->buffer, oe->buffer_idx, oe);
+	}
 
 	/* ... and continue with the rest */
 	list_for_each_entry_safe(buffer, tmp, &oe->to_free, list) {