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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pointer to a request that is no longer valid.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: 0a5aa8d161 ("block: fix blk_mq_attempt_bio_merge and rq_qos_throttle protection")
Reported-by: Dylan Yudaken <dylany@fb.com>
Tested-by: Dylan Yudaken <dylany@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2022-06-21 10:03:57 -06:00
parent 9243fc4cd2
commit 2645672ffe
1 changed files with 8 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
block/blk-mq.c
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@ -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;
}