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Commit 3c782d67 authored by Jens Axboe's avatar Jens Axboe
Browse files

blk-mq: fix potential race in queue restart and driver tag allocation 



Once we mark the queue as needing a restart, re-check if we can
get a driver tag. This fixes a theoretical issue where the needed
IO completes _after_ blk_mq_get_driver_tag() fails, but before we
manage to set the restart bit.

Signed-off-by: default avatarJens Axboe <axboe@fb.com>
Reviewed-by: default avatarOmar Sandoval <osandov@fb.com>
Tested-by: default avatarHannes Reinecke <hare@suse.com>
parent 0abad774

block/blk-mq.c

+9 −1
Original line number Diff line number Diff line
@@ -928,7 +928,15 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list) 
		if (!blk_mq_get_driver_tag(rq, &hctx, false)) {

			if (!queued && reorder_tags_to_front(list))

				continue;



			/*

			 * We failed getting a driver tag. Mark the queue(s)

			 * as needing a restart. Retry getting a tag again,

			 * in case the needed IO completed right before we

			 * marked the queue as needing a restart.

			 */

			blk_mq_sched_mark_restart(hctx);

			if (!blk_mq_get_driver_tag(rq, &hctx, false))

				break;

		}

		list_del_init(&rq->queuelist);