On 8/28/18 11:54 AM, Omar Sandoval wrote:

On Mon, Aug 27, 2018 at 08:52:34AM -0600, Jens Axboe wrote:

quoted

On 8/27/18 1:24 AM, Ming Lei wrote:

quoted

Hi,

There is fundamental issue in commit 328728630d9f2bf1 (scsi: core: avoid
host-wide host_busy counter for scsi_mq) because SCSI's host busy counter
may not be same with counter of blk-mq's inflight tags, especially in case
of none io scheduler.

So please revert the two commits.

Please do, they break changing write cache mode on my SATA drives. You
can add my tested-by and/or reported-by to this.

Jens, how does it break? Could we add a blktest for it?

Yep, it's pretty easy:

# echo "write through" > /sys/block/sde/device/scsi_disk/4:0:0:0/cache_type

and it hangs. For a blktests test, probably check the current value and
ensure we set it to a different value, then restore it.

-- 
Jens Axboe