Hi, Was testing other things today, but ended up with this: # echo "write through" > /sys/block/sde/device/scsi_disk/4:0:0:0/cache_type hanging. Looking closer, the request is successfully queued and the caller is waiting on rq execution and completion, but the request is sitting in the hctx->dispatch list and is continually being attempted issued, but gets a BLK_STS_RESOURCE return. The problematic commit is: commit 328728630d9f2bf14b82ca30b5e47489beefe361 Author: Ming Lei <ming.lei@xxxxxxxxxx> Date: Sun Jun 24 22:03:27 2018 +0800 scsi: core: avoid host-wide host_busy counter for scsi_mq so I'm guessing it's some one-off or similar. I won't have more time to look into this today, so might have to wait until Monday. -- Jens Axboe