fs: dlm: clear pending bit when queue was empty

This patch clears the DLM_IFL_CB_PENDING_BIT flag which will be set when
there is callback work queued when there was no callback to dequeue. It
is a buggy case and should never happen, that's why there is a
WARN_ON(). However if the case happens we are prepared to somehow
recover from it.

Cc: stable@vger.kernel.org
Fixes: 61bed0ba ("fs: dlm: use a non-static queue for callbacks")
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>

fs/dlm/ast.c

@@ -181,10 +181,12 @@ void dlm_callback_work(struct work_struct *work)
 
 	spin_lock(&lkb->lkb_cb_lock);
 	rv = dlm_dequeue_lkb_callback(lkb, &cb);
-	spin_unlock(&lkb->lkb_cb_lock);
-
-	if (WARN_ON_ONCE(rv == DLM_DEQUEUE_CALLBACK_EMPTY))
+	if (WARN_ON_ONCE(rv == DLM_DEQUEUE_CALLBACK_EMPTY)) {
+		clear_bit(DLM_IFL_CB_PENDING_BIT, &lkb->lkb_iflags);
+		spin_unlock(&lkb->lkb_cb_lock);
 		goto out;
+	}
+	spin_unlock(&lkb->lkb_cb_lock);
 
 	for (;;) {
 		castfn = lkb->lkb_astfn;