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commit1c05839aa9upstream. This fixes a regression added with: commite9e006f5fcAuthor: 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:e9e006f5fc("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>