Commit 2645672f authored by Jens Axboe's avatar Jens Axboe
Browse files

block: pop cached rq before potentially blocking rq_qos_throttle() 



If rq_qos_throttle() ends up blocking, then we will have invalidated and
flushed our current plug. Since blk_mq_get_cached_request() hasn't
popped the cached request off the plug list just yet, we end holding a
pointer to a request that is no longer valid. This insta-crashes with
rq->mq_hctx being NULL in the validity checks just after.

Pop the request off the cached list before doing rq_qos_throttle() to
avoid using a potentially stale request.

Fixes: 0a5aa8d1 ("block: fix blk_mq_attempt_bio_merge and rq_qos_throttle protection")
Reported-by: default avatarDylan Yudaken <dylany@fb.com>
Tested-by: default avatarDylan Yudaken <dylany@fb.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 9243fc4c

block/blk-mq.c

+8 −3
Original line number Diff line number Diff line
@@ -2765,15 +2765,20 @@ static inline struct request *blk_mq_get_cached_request(struct request_queue *q, 
		return NULL;

	}



	rq_qos_throttle(q, *bio);



	if (blk_mq_get_hctx_type((*bio)->bi_opf) != rq->mq_hctx->type)

		return NULL;

	if (op_is_flush(rq->cmd_flags) != op_is_flush((*bio)->bi_opf))

		return NULL;



	rq->cmd_flags = (*bio)->bi_opf;

	/*

	 * If any qos ->throttle() end up blocking, we will have flushed the

	 * plug and hence killed the cached_rq list as well. Pop this entry

	 * before we throttle.

	 */

	plug->cached_rq = rq_list_next(rq);

	rq_qos_throttle(q, *bio);



	rq->cmd_flags = (*bio)->bi_opf;

	INIT_LIST_HEAD(&rq->queuelist);

	return rq;

}