Commit d3cfb2a0 authored Mar 27, 2017 by Ming Lei Committed by Jens Axboe Mar 29, 2017

block: block new I/O just after queue is set as dying



Before commit 780db207(blk-mq: decouble blk-mq freezing
from generic bypassing), the dying flag is checked before
entering queue, and Tejun converts the checking into .mq_freeze_depth,
and assumes the counter is increased just after dying flag
is set. Unfortunately we doesn't do that in blk_set_queue_dying().

This patch calls blk_freeze_queue_start() in blk_set_queue_dying(),
so that we can block new I/O coming once the queue is set as dying.

Given blk_set_queue_dying() is always called in remove path
of block device, and queue will be cleaned up later, we don't
need to worry about undoing the counter.

Cc: Tejun Heo <tj@kernel.org>
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 1671d522

block/blk-core.c

+10 −3

Original line number	Diff line number	Diff line
		@@ -500,6 +500,13 @@ void blk_set_queue_dying(struct request_queue *q)
		queue_flag_set(QUEUE_FLAG_DYING, q);
		spin_unlock_irq(q->queue_lock);

		/*
		* When queue DYING flag is set, we need to block new req
		* entering queue, so we call blk_freeze_queue_start() to
		* prevent I/O from crossing blk_queue_enter().
		*/
		blk_freeze_queue_start(q);

		if (q->mq_ops)
		blk_mq_wake_waiters(q);
		else {
		@@ -672,9 +679,9 @@ int blk_queue_enter(struct request_queue *q, bool nowait)
		/*
		* read pair of barrier in blk_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.
		* .q_usage_counter and reading .mq_freeze_depth or
		* queue dying flag, otherwise the following wait may
		* never return if the two reads are reordered.
		*/
		smp_rmb();

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