Commit 1c05839a authored Dec 08, 2019 by Mike Christie Committed by Jens Axboe Dec 16, 2019

nbd: fix shutdown and recv work deadlock v2



This fixes a regression added with:

commit e9e006f5
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: e9e006f5 ("nbd: fix max number of supported devs")
Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent d7bd15a1

drivers/block/nbd.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -1296,10 +1296,10 @@ static int nbd_start_device_ioctl(struct nbd_device nbd, struct block_device b
		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);
		}

		mutex_lock(&nbd->config_lock);
		nbd_bdev_reset(bdev);
		/* user requested, ignore socket errors */

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