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nbd: fix shutdown and recv work deadlock v2

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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>
This commit is contained in:
Mike Christie 2019-12-08 16:51:50 -06:00 committed by Greg Kroah-Hartman
parent 5a07ace737
commit d1db913b04
1 changed files with 3 additions and 3 deletions
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6
drivers/block/nbd.c
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@ -1234,10 +1234,10 @@ 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);
}
flush_workqueue(nbd->recv_workq);
mutex_lock(&nbd->config_lock);
bd_set_size(bdev, 0);
/* user requested, ignore socket errors */