Commit 538b7534 authored Sep 16, 2014 by Jens Axboe

blk-mq: request deadline must be visible before marking rq as started



When we start the request, we set the deadline and flip the bits
marking the request as started and non-complete. However, it's
important that the deadline store is ordered before flipping the
bits, otherwise we could have a small window where the request is
marked started but with an invalid deadline. This can confuse the
timeout handling.

Suggested-by: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

parent 37504a3b

block/blk-mq.c

+6 −0

Original line number	Original line	Diff line number	Diff line
	@@ -392,6 +392,12 @@ static void blk_mq_start_request(struct request *rq, bool last)

	blk_add_timer(rq);		blk_add_timer(rq);

			/*
			* Ensure that ->deadline is visible before set the started
			* flag and clear the completed flag.
			*/
			smp_mb__before_atomic();

	/*		/*
	* Mark us as started and clear complete. Complete might have been		* Mark us as started and clear complete. Complete might have been
	* set if requeue raced with timeout, which then marked it as		* set if requeue raced with timeout, which then marked it as