Commit 050735b0 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

perf: Fix exit() vs PERF_FORMAT_GROUP 



Both Stephane and Corey reported that PERF_FORMAT_GROUP didn't
work as expected if the task the counters were attached to quit
before the read() call.

The cause is that we unconditionally destroy the grouping when
we remove counters from their context. Fix this by splitting off
the group destroy from the list removal such that
perf_event_remove_from_context() does not do this and change
perf_event_release() to do so.

Reported-by: default avatarCorey Ashford <cjashfor@linux.vnet.ibm.com>
Reported-by: default avatarStephane Eranian <eranian@google.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: <stable@kernel.org> # .34.x
LKML-Reference: <1273571513.5605.3527.camel@twins>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent e3174cfd

kernel/perf_event.c

+16 −3
Original line number Diff line number Diff line
@@ -308,8 +308,6 @@ list_add_event(struct perf_event *event, struct perf_event_context *ctx) 
static void

list_del_event(struct perf_event *event, struct perf_event_context *ctx)

{

	struct perf_event *sibling, *tmp;



	if (list_empty(&event->group_entry))

		return;

	ctx->nr_events--;
@@ -333,6 +331,12 @@ list_del_event(struct perf_event *event, struct perf_event_context *ctx) 
	 */

	if (event->state > PERF_EVENT_STATE_OFF)

		event->state = PERF_EVENT_STATE_OFF;

}



static void

perf_destroy_group(struct perf_event *event, struct perf_event_context *ctx)

{

	struct perf_event *sibling, *tmp;



	/*

	 * If this was a group event with sibling events then
@@ -1868,6 +1872,12 @@ int perf_event_release_kernel(struct perf_event *event) 
{

	struct perf_event_context *ctx = event->ctx;



	/*

	 * Remove from the PMU, can't get re-enabled since we got

	 * here because the last ref went.

	 */

	perf_event_disable(event);



	WARN_ON_ONCE(ctx->parent_ctx);

	/*

	 * There are two ways this annotation is useful:
@@ -1882,7 +1892,10 @@ int perf_event_release_kernel(struct perf_event *event) 
	 *     to trigger the AB-BA case.

	 */

	mutex_lock_nested(&ctx->mutex, SINGLE_DEPTH_NESTING);

	perf_event_remove_from_context(event);

	raw_spin_lock_irq(&ctx->lock);

	list_del_event(event, ctx);

	perf_destroy_group(event, ctx);

	raw_spin_unlock_irq(&ctx->lock);

	mutex_unlock(&ctx->mutex);



	mutex_lock(&event->owner->perf_event_mutex);

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