perf: Use tracepoint_synchronize_unregister() to flush any pending tracepoint call

We use synchronize_sched() to ensure a tracepoint won't be called
while/after we release the perf buffers it references.

But the tracepoint API has its own API for that:
tracepoint_synchronize_unregister(). Use it instead as it's
self-explanatory and eases maintainance.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>

kernel/trace/trace_event_perf.c

@@ -131,10 +131,10 @@ void perf_trace_destroy(struct perf_event *p_event)
 	tp_event->class->reg(tp_event, TRACE_REG_PERF_UNREGISTER);
 
 	/*
-	 * Ensure our callback won't be called anymore. See
-	 * tracepoint_probe_unregister() and __DO_TRACE().
+	 * Ensure our callback won't be called anymore. The buffers
+	 * will be freed after that.
 	 */
-	synchronize_sched();
+	tracepoint_synchronize_unregister();
 
 	free_percpu(tp_event->perf_events);
 	tp_event->perf_events = NULL;