From: Ilya Dryomov idryomov@gmail.com
commit ed9eb71085ecb7ded9a5118cec2ab70667cc7350 upstream.
Currently rbd_quiesce_lock() holds lock_rwsem for read while blocking on releasing_wait completion. On the I/O completion side, each image request also needs to take lock_rwsem for read. Because rw_semaphore implementation doesn't allow new readers after a writer has indicated interest in the lock, this can result in a deadlock if something that needs to take lock_rwsem for write gets involved. For example:
1. watch error occurs 2. rbd_watch_errcb() takes lock_rwsem for write, clears owner_cid and releases lock_rwsem 3. after reestablishing the watch, rbd_reregister_watch() takes lock_rwsem for write and calls rbd_reacquire_lock() 4. rbd_quiesce_lock() downgrades lock_rwsem to for read and blocks on releasing_wait until running_list becomes empty 5. another watch error occurs 6. rbd_watch_errcb() blocks trying to take lock_rwsem for write 7. no in-flight image request can complete and delete itself from running_list because lock_rwsem won't be granted anymore
A similar scenario can occur with "lock has been acquired" and "lock has been released" notification handers which also take lock_rwsem for write to update owner_cid.
We don't actually get anything useful from sitting on lock_rwsem in rbd_quiesce_lock() -- owner_cid updates certainly don't need to be synchronized with. In fact the whole owner_cid tracking logic could probably be removed from the kernel client because we don't support proxied maintenance operations.
Cc: stable@vger.kernel.org # 5.3+ URL: https://tracker.ceph.com/issues/42757 Signed-off-by: Ilya Dryomov idryomov@gmail.com Tested-by: Robin Geuze robin.geuze@nl.team.blue Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/block/rbd.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-)
--- a/drivers/block/rbd.c +++ b/drivers/block/rbd.c @@ -4239,8 +4239,6 @@ again:
static bool rbd_quiesce_lock(struct rbd_device *rbd_dev) { - bool need_wait; - dout("%s rbd_dev %p\n", __func__, rbd_dev); lockdep_assert_held_write(&rbd_dev->lock_rwsem);
@@ -4252,11 +4250,11 @@ static bool rbd_quiesce_lock(struct rbd_ */ rbd_dev->lock_state = RBD_LOCK_STATE_RELEASING; rbd_assert(!completion_done(&rbd_dev->releasing_wait)); - need_wait = !list_empty(&rbd_dev->running_list); - downgrade_write(&rbd_dev->lock_rwsem); - if (need_wait) - wait_for_completion(&rbd_dev->releasing_wait); - up_read(&rbd_dev->lock_rwsem); + if (list_empty(&rbd_dev->running_list)) + return true; + + up_write(&rbd_dev->lock_rwsem); + wait_for_completion(&rbd_dev->releasing_wait);
down_write(&rbd_dev->lock_rwsem); if (rbd_dev->lock_state != RBD_LOCK_STATE_RELEASING)