rbd: don't assume RBD_LOCK_STATE_LOCKED for exclusive mappings

Every time a watch is reestablished after getting lost, we need to
update the cookie which involves quiescing exclusive lock.  For this,
we transition from RBD_LOCK_STATE_LOCKED to RBD_LOCK_STATE_QUIESCING
roughly for the duration of rbd_reacquire_lock() call.  If the mapping
is exclusive and I/O happens to arrive in this time window, it's failed
with EROFS (later translated to EIO) based on the wrong assumption in
rbd_img_exclusive_lock() -- "lock got released?" check there stopped
making sense with commit a2b1da0 ("rbd: lock should be quiesced on
reacquire").

To make it worse, any such I/O is added to the acquiring list before
EROFS is returned and this sets up for violating rbd_lock_del_request()
precondition that the request is either on the running list or not on
any list at all -- see commit ded080c ("rbd: don't move requests
to the running list on errors").  rbd_lock_del_request() ends up
processing these requests as if they were on the running list which
screws up quiescing_wait completion counter and ultimately leads to

    rbd_assert(!completion_done(&rbd_dev->quiescing_wait));

being triggered on the next watch error.

Cc: [email protected] # 06ef84c4e9c4: rbd: rename RBD_LOCK_STATE_RELEASING and releasing_wait
Cc: [email protected]
Fixes: 637cd06 ("rbd: new exclusive lock wait/wake code")
Signed-off-by: Ilya Dryomov <[email protected]>
Reviewed-by: Dongsheng Yang <[email protected]>

Author: idryomov

drivers/block/rbd.c

@@ -3457,6 +3457,7 @@ static void rbd_lock_del_request(struct rbd_img_request *img_req)
 	lockdep_assert_held(&rbd_dev->lock_rwsem);
 	spin_lock(&rbd_dev->lock_lists_lock);
 	if (!list_empty(&img_req->lock_item)) {
+		rbd_assert(!list_empty(&rbd_dev->running_list));
 		list_del_init(&img_req->lock_item);
 		need_wakeup = (rbd_dev->lock_state == RBD_LOCK_STATE_QUIESCING &&
 			       list_empty(&rbd_dev->running_list));
@@ -3476,11 +3477,6 @@ static int rbd_img_exclusive_lock(struct rbd_img_request *img_req)
 	if (rbd_lock_add_request(img_req))
 		return 1;
 
-	if (rbd_dev->opts->exclusive) {
-		WARN_ON(1); /* lock got released? */
-		return -EROFS;
-	}
-
 	/*
 	 * Note the use of mod_delayed_work() in rbd_acquire_lock()
 	 * and cancel_delayed_work() in wake_lock_waiters().
@@ -4601,6 +4597,10 @@ static void rbd_reacquire_lock(struct rbd_device *rbd_dev)
 			rbd_warn(rbd_dev, "failed to update lock cookie: %d",
 				 ret);
 
+		if (rbd_dev->opts->exclusive)
+			rbd_warn(rbd_dev,
+			     "temporarily releasing lock on exclusive mapping");
+
 		/*
 		 * Lock cookie cannot be updated on older OSDs, so do
 		 * a manual release and queue an acquire.