perf/aux: Fix AUX output stopping

Commit:

  8a58dda ("perf/core: Fix exclusive events' grouping")

allows CAP_EXCLUSIVE events to be grouped with other events. Since all
of those also happen to be AUX events (which is not the case the other
way around, because arch/s390), this changes the rules for stopping the
output: the AUX event may not be on its PMU's context any more, if it's
grouped with a HW event, in which case it will be on that HW event's
context instead. If that's the case, munmap() of the AUX buffer can't
find and stop the AUX event, potentially leaving the last reference with
the atomic context, which will then end up freeing the AUX buffer. This
will then trip warnings:

Fix this by using the context's PMU context when looking for events
to stop, instead of the event's PMU context.

Signed-off-by: Alexander Shishkin <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vince Weaver <[email protected]>
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

Author: virtuoso

kernel/events/core.c

@@ -6949,7 +6949,7 @@ static void __perf_event_output_stop(struct perf_event *event, void *data)
 static int __perf_pmu_output_stop(void *info)
 {
 	struct perf_event *event = info;
-	struct pmu *pmu = event->pmu;
+	struct pmu *pmu = event->ctx->pmu;
 	struct perf_cpu_context *cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
 	struct remote_output ro = {
 		.rb	= event->rb,