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Commit f73e22ab authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

perf: Fix races in computing the header sizes 



There are two races with the current code:

 - Another event can join the group and compute a larger header_size
   concurrently, if the smaller store wins we'll have an incorrect
   header_size set.

 - We compute the header_size after the event becomes active,
   therefore its possible to use the size before its computed.

Remedy the first by moving the computation inside the ctx::mutex lock,
and the second by placing it _before_ perf_install_in_context().

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent a723968c

kernel/events/core.c

+9 −6
Original line number Original line Diff line number Diff line
@@ -8399,6 +8399,15 @@ SYSCALL_DEFINE5(perf_event_open, 
		put_ctx(gctx);

		put_ctx(gctx);

	}

	}





	/*

	 * Precalculate sample_data sizes; do while holding ctx::mutex such

	 * that we're serialized against further additions and before

	 * perf_install_in_context() which is the point the event is active and

	 * can use these values.

	 */

	perf_event__header_size(event);

	perf_event__id_header_size(event);



	perf_install_in_context(ctx, event, event->cpu);

	perf_install_in_context(ctx, event, event->cpu);

	perf_unpin_context(ctx);

	perf_unpin_context(ctx);
@@ -8414,12 +8423,6 @@ SYSCALL_DEFINE5(perf_event_open, 
	list_add_tail(&event->owner_entry, &current->perf_event_list);

	list_add_tail(&event->owner_entry, &current->perf_event_list);

	mutex_unlock(&current->perf_event_mutex);

	mutex_unlock(&current->perf_event_mutex);





	/*

	 * Precalculate sample_data sizes

	 */

	perf_event__header_size(event);

	perf_event__id_header_size(event);



	/*

	/*

	 * Drop the reference on the group_event after placing the

	 * Drop the reference on the group_event after placing the

	 * new event on the sibling_list. This ensures destruction

	 * new event on the sibling_list. This ensures destruction