Re: [PATCH] nbd: fix shutdown and recv work deadlock v2

[Jens Axboe <axboe@kernel.dk>]

On 12/8/19 3:51 PM, Mike Christie wrote:
> This fixes a regression added with:
> 
> commit e9e006f5fcf2bab59149cb38a48a4817c1b538b4
> Author: Mike Christie <mchristi@redhat.com>
> Date:   Sun Aug 4 14:10:06 2019 -0500
> 
>     nbd: fix max number of supported devs
> 
> where we can deadlock during device shutdown. The problem occurs if
> the recv_work's nbd_config_put occurs after nbd_start_device_ioctl has
> returned and the userspace app has droppped its reference via closing
> the device and running nbd_release. The recv_work nbd_config_put call
> would then drop the refcount to zero and try to destroy the config which
> would try to do destroy_workqueue from the recv work.
> 
> This patch just has nbd_start_device_ioctl do a flush_workqueue when it
> wakes so we know after the ioctl returns running works have exited. This
> also fixes a possible race where we could try to reuse the device while
> old recv_works are still running.

Applied, thanks Mike.

-- 
Jens Axboe