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block: add a read barrier in blk_queue_enter() 

Without the barrier, reading DEAD flag of .q_usage_counter
and reading .mq_freeze_depth may be reordered, then the
following wait_event_interruptible() may never return.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Bart Van Assche <bart.vanassche@sandisk.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Ming Lei 2017-03-27 20:06:56 +08:00 committed by Jens Axboe
parent d9d149a396
commit 5ed61d3f08
1 changed files with 9 additions and 0 deletions
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9
block/blk-core.c
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@ -669,6 +669,15 @@ int blk_queue_enter(struct request_queue *q, bool nowait)
if (nowait)
return -EBUSY;
/*
* read pair of barrier in blk_mq_freeze_queue_start(),
* we need to order reading __PERCPU_REF_DEAD flag of
* .q_usage_counter and reading .mq_freeze_depth,
* otherwise the following wait may never return if the
* two reads are reordered.
*/
smp_rmb();
ret = wait_event_interruptible(q->mq_freeze_wq,
!atomic_read(&q->mq_freeze_depth) ||
blk_queue_dying(q));