nbd: fix circular lock dependency in nbd_disconnect_and_put#1022
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nbd: fix circular lock dependency in nbd_disconnect_and_put#1022blktests-ci[bot] wants to merge 1 commit into
blktests-ci[bot] wants to merge 1 commit into
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Move flush_workqueue() out of the config_lock critical section in
nbd_disconnect_and_put() to break a circular lock dependency.
The lockdep splat shows:
config_lock -> (wq_completion)nbd0-recv
from nbd_disconnect_and_put() holding config_lock then calling
flush_workqueue() which waits for recv_work to complete.
(work_completion)(&args->work) -> config_lock
from recv_work() -> nbd_config_put() -> refcount_dec_and_mutex_lock()
which may acquire config_lock when the last reference is dropped.
Fix by splitting the config_lock region: first hold config_lock to
perform nbd_disconnect(), sock_shutdown(), and clear NBD_RT_BOUND (to
prevent nbd_genl_reconfigure from queueing new recv_work during the
window), then release config_lock before flush_workqueue(), and
re-acquire it for nbd_clear_que(). This is safe because:
- sock_shutdown() ensures recv_work will observe errors and exit
- NBD_RT_BOUND cleared prevents concurrent reconfigure from reconnecting
- flush_workqueue() guarantees all recv_work has completed before
the second config_lock section clears the queue
Fixes: e2daec4 ("nbd: Fix hungtask when nbd_config_put")
Reported-by: syzbot+3add0454d5a2619b8e80@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=3add0454d5a2619b8e80
Signed-off-by: Yun Zhou <yun.zhou@windriver.com>
Author
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Upstream branch: dc59e4f |
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Pull request for series with
subject: nbd: fix circular lock dependency in nbd_disconnect_and_put
version: 1
url: https://patchwork.kernel.org/project/linux-block/list/?series=1118610