On Jun 21, 2022 / 10:07, Jens Axboe wrote:
> 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 pointer to a request that is no longer valid.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>
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Thank you for the fix and sorry for the trouble. The patch passed my test set:
Tested-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@xxxxxxx>
BTW, may I know the workload or script which triggers the failure? I'm
interested in if we can add a blktests test case to exercises qos throttle
and prevent similar bugs in the future.
--
Shin'ichiro Kawasaki
