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Subject[PATCH 5.18 084/181] block: pop cached rq before potentially blocking rq_qos_throttle()
Date
From: Jens Axboe <axboe@kernel.dk>

[ 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pointer to a request that is no longer valid.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@fb.com>
Tested-by: Dylan Yudaken <dylany@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
block/blk-mq.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

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;
}
--
2.35.1


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