blk-mq: fix potential race in queue restart and driver tag allocation (3c782d67) · Commits · 戴 / test

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:

Jens Axboe <axboe@fb.com> Reviewed-by:

Omar Sandoval <osandov@fb.com> Tested-by:

Hannes Reinecke <hare@suse.com>

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);

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