rbd: don't assume rbd_is_lock_owner() for exclusive mappings

Expanding on the previous commit, assuming that rbd_is_lock_owner()
always returns true (i.e. that we are either in RBD_LOCK_STATE_LOCKED
or RBD_LOCK_STATE_QUIESCING) if the mapping is exclusive is wrong too.
In case ceph_cls_set_cookie() fails, the lock would be temporarily
released even if the mapping is exclusive, meaning that we can end up
even in RBD_LOCK_STATE_UNLOCKED.

IOW, exclusive mappings are really "just" about disabling automatic
lock transitions (as documented in the man page), not about grabbing
the lock and holding on to it whatever it takes.

Cc: stable@vger.kernel.org
Fixes: 637cd060 ("rbd: new exclusive lock wait/wake code")
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Dongsheng Yang <dongsheng.yang@easystack.cn>

drivers/block/rbd.c

@@ -6589,11 +6589,6 @@ static int rbd_add_acquire_lock(struct rbd_device *rbd_dev)
 	if (ret)
 		return ret;
 
-	/*
-	 * The lock may have been released by now, unless automatic lock
-	 * transitions are disabled.
-	 */
-	rbd_assert(!rbd_dev->opts->exclusive || rbd_is_lock_owner(rbd_dev));
 	return 0;
 }