This is a note to let you know that I've just added the patch titled block: pop cached rq before potentially blocking rq_qos_throttle() to the 5.18-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: block-pop-cached-rq-before-potentially-blocking-rq_q.patch and it can be found in the queue-5.18 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 450750df0a575f36337994d3cbfa35d0343ee85a Author: Jens Axboe <axboe@xxxxxxxxx> Date: Tue Jun 21 10:03:57 2022 -0600 block: pop cached rq before potentially blocking rq_qos_throttle() [ Upstream commit 2645672ffe21f0a1c139bfbc05ad30fd4e4f2583 ] 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hasn't popped the cached request off the plug list just yet, we end holding a pointer to a request that is no longer valid.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: 0a5aa8d161d1 ("block: fix blk_mq_attempt_bio_merge and rq_qos_throttle protection") Reported-by: Dylan Yudaken <dylany@xxxxxx> Tested-by: Dylan Yudaken <dylany@xxxxxx> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/block/blk-mq.c b/block/blk-mq.c index 631fb87b4976..37caa73bff89 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2777,15 +2777,20 @@ 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; }