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

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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>
This commit is contained in:
Jens Axboe 2014-09-16 10:37:37 -06:00
parent 37504a3be9
commit 538b753418
1 changed files with 6 additions and 0 deletions
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6
block/blk-mq.c
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@ -392,6 +392,12 @@ static void blk_mq_start_request(struct request *rq, bool last)
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
* set if requeue raced with timeout, which then marked it as