Commit fb350e0a authored Jan 06, 2018 by Ming Lei Committed by Jens Axboe Jan 06, 2018

blk-mq: fix race between updating nr_hw_queues and switching io sched



In both elevator_switch_mq() and blk_mq_update_nr_hw_queues(), sched tags
can be allocated, and q->nr_hw_queue is used, and race is inevitable, for
example: blk_mq_init_sched() may trigger use-after-free on hctx, which is
freed in blk_mq_realloc_hw_ctxs() when nr_hw_queues is decreased.

This patch fixes the race be holding q->sysfs_lock.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reported-by: Yi Zhang <yi.zhang@redhat.com>
Tested-by: Yi Zhang <yi.zhang@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent 7d4901a9

block/blk-mq.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -2407,6 +2407,9 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
		struct blk_mq_hw_ctx **hctxs = q->queue_hw_ctx;

		blk_mq_sysfs_unregister(q);

		/* protect against switching io scheduler */
		mutex_lock(&q->sysfs_lock);
		for (i = 0; i < set->nr_hw_queues; i++) {
		int node;

		@@ -2451,6 +2454,7 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
		}
		}
		q->nr_hw_queues = i;
		mutex_unlock(&q->sysfs_lock);
		blk_mq_sysfs_register(q);
		}