Commit 5ed61d3f authored Mar 27, 2017 by Ming Lei Committed by Jens Axboe Mar 29, 2017

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>

parent d9d149a3

block/blk-core.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -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));

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