From: Mike Christie mchristi@redhat.com
commit 1c05839aa973cfae8c3db964a21f9c0eef8fcc21 upstream.
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.
Cc: stable@vger.kernel.org Fixes: e9e006f5fcf2 ("nbd: fix max number of supported devs") Signed-off-by: Mike Christie mchristi@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/block/nbd.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
--- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -1234,10 +1234,10 @@ static int nbd_start_device_ioctl(struct mutex_unlock(&nbd->config_lock); ret = wait_event_interruptible(config->recv_wq, atomic_read(&config->recv_threads) == 0); - if (ret) { + if (ret) sock_shutdown(nbd); - flush_workqueue(nbd->recv_workq); - } + flush_workqueue(nbd->recv_workq); + mutex_lock(&nbd->config_lock); bd_set_size(bdev, 0); /* user requested, ignore socket errors */