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Commit f5bbbbe4 authored by Jianchao Wang's avatar Jianchao Wang Committed by Jens Axboe
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blk-mq: sync the update nr_hw_queues with blk_mq_queue_tag_busy_iter 



For blk-mq, part_in_flight/rw will invoke blk_mq_in_flight/rw to
account the inflight requests. It will access the queue_hw_ctx and
nr_hw_queues w/o any protection. When updating nr_hw_queues and
blk_mq_in_flight/rw occur concurrently, panic comes up.

Before update nr_hw_queues, the q will be frozen. So we could use
q_usage_counter to avoid the race. percpu_ref_is_zero is used here
so that we will not miss any in-flight request. The access to
nr_hw_queues and queue_hw_ctx in blk_mq_queue_tag_busy_iter are
under rcu critical section, __blk_mq_update_nr_hw_queues could use
synchronize_rcu to ensure the zeroed q_usage_counter to be globally
visible.

Signed-off-by: default avatarJianchao Wang <jianchao.w.wang@oracle.com>
Reviewed-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent d48ece20

block/blk-mq-tag.c

+13 −1
Original line number Diff line number Diff line
@@ -320,6 +320,18 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn, 
	struct blk_mq_hw_ctx *hctx;

	int i;



	/*

	 * __blk_mq_update_nr_hw_queues will update the nr_hw_queues and

	 * queue_hw_ctx after freeze the queue. So we could use q_usage_counter

	 * to avoid race with it. __blk_mq_update_nr_hw_queues will users

	 * synchronize_rcu to ensure all of the users go out of the critical

	 * section below and see zeroed q_usage_counter.

	 */

	rcu_read_lock();

	if (percpu_ref_is_zero(&q->q_usage_counter)) {

		rcu_read_unlock();

		return;

	}



	queue_for_each_hw_ctx(q, hctx, i) {

		struct blk_mq_tags *tags = hctx->tags;
@@ -335,7 +347,7 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn, 
			bt_for_each(hctx, &tags->breserved_tags, fn, priv, true);

		bt_for_each(hctx, &tags->bitmap_tags, fn, priv, false);

	}



	rcu_read_unlock();

}



static int bt_alloc(struct sbitmap_queue *bt, unsigned int depth,

block/blk-mq.c

+4 −0
Original line number Diff line number Diff line
@@ -2976,6 +2976,10 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, 


	list_for_each_entry(q, &set->tag_list, tag_set_list)

		blk_mq_freeze_queue(q);

	/*

	 * Sync with blk_mq_queue_tag_busy_iter.

	 */

	synchronize_rcu();

	/*

	 * Switch IO scheduler to 'none', cleaning up the data associated

	 * with the previous scheduler. We will switch back once we are done