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Commit 9886167d authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

perf: Fix perf_pmu_migrate_context 



While auditing the list_entry usage due to a trinity bug I found that
perf_pmu_migrate_context violates the rules for
perf_event::event_entry.

The problem is that perf_event::event_entry is a RCU list element, and
hence we must wait for a full RCU grace period before re-using the
element after deletion.

Therefore the usage in perf_pmu_migrate_context() which re-uses the
entry immediately is broken. For now introduce another list_head into
perf_event for this specific usage.

This doesn't actually fix the trinity report because that never goes
through this code.

Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-mkj72lxagw1z8fvjm648iznw@git.kernel.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent cac66535

include/linux/perf_event.h

+23 −1
Original line number Original line Diff line number Diff line
@@ -294,9 +294,31 @@ struct ring_buffer; 
 */

 */

struct perf_event {

struct perf_event {

#ifdef CONFIG_PERF_EVENTS

#ifdef CONFIG_PERF_EVENTS

	struct list_head		group_entry;

	/*

	 * entry onto perf_event_context::event_list;

	 *   modifications require ctx->lock

	 *   RCU safe iterations.

	 */

	struct list_head		event_entry;

	struct list_head		event_entry;



	/*

	 * XXX: group_entry and sibling_list should be mutually exclusive;

	 * either you're a sibling on a group, or you're the group leader.

	 * Rework the code to always use the same list element.

	 *

	 * Locked for modification by both ctx->mutex and ctx->lock; holding

	 * either sufficies for read.

	 */

	struct list_head		group_entry;

	struct list_head		sibling_list;

	struct list_head		sibling_list;



	/*

	 * We need storage to track the entries in perf_pmu_migrate_context; we

	 * cannot use the event_entry because of RCU and we want to keep the

	 * group in tact which avoids us using the other two entries.

	 */

	struct list_head		migrate_entry;



	struct hlist_node		hlist_entry;

	struct hlist_node		hlist_entry;

	int				nr_siblings;

	int				nr_siblings;

	int				group_flags;

	int				group_flags;

kernel/events/core.c

+3 −3
Original line number Original line Diff line number Diff line
@@ -7234,15 +7234,15 @@ void perf_pmu_migrate_context(struct pmu *pmu, int src_cpu, int dst_cpu) 
		perf_remove_from_context(event);

		perf_remove_from_context(event);

		unaccount_event_cpu(event, src_cpu);

		unaccount_event_cpu(event, src_cpu);

		put_ctx(src_ctx);

		put_ctx(src_ctx);

		list_add(&event->event_entry, &events);

		list_add(&event->migrate_entry, &events);

	}

	}

	mutex_unlock(&src_ctx->mutex);

	mutex_unlock(&src_ctx->mutex);





	synchronize_rcu();

	synchronize_rcu();





	mutex_lock(&dst_ctx->mutex);

	mutex_lock(&dst_ctx->mutex);

	list_for_each_entry_safe(event, tmp, &events, event_entry) {

	list_for_each_entry_safe(event, tmp, &events, migrate_entry) {

		list_del(&event->event_entry);

		list_del(&event->migrate_entry);

		if (event->state >= PERF_EVENT_STATE_OFF)

		if (event->state >= PERF_EVENT_STATE_OFF)

			event->state = PERF_EVENT_STATE_INACTIVE;

			event->state = PERF_EVENT_STATE_INACTIVE;

		account_event_cpu(event, dst_cpu);

		account_event_cpu(event, dst_cpu);