[DLM] fix requestqueue race

Red Hat BZ 211914

There's a race between dlm_recoverd (1) enabling locking and (2) clearing
out the requestqueue, and dlm_recvd (1) checking if locking is enabled and
(2) adding a message to the requestqueue.  An order of recoverd(1),
recvd(1), recvd(2), recoverd(2) will result in a message being left on the
requestqueue.  The fix is to have dlm_recvd check if dlm_recoverd has
enabled locking after taking the mutex for the requestqueue and if it has
processing the message instead of queueing it.

Signed-off-by: David Teigland <teigland@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/dlm/lock.c

@@ -3028,10 +3028,17 @@ int dlm_receive_message(struct dlm_header *hd, int nodeid, int recovery)
 
 	while (1) {
 		if (dlm_locking_stopped(ls)) {
-			if (!recovery)
-				dlm_add_requestqueue(ls, nodeid, hd);
-			error = -EINTR;
-			goto out;
+			if (recovery) {
+				error = -EINTR;
+				goto out;
+			}
+			error = dlm_add_requestqueue(ls, nodeid, hd);
+			if (error == -EAGAIN)
+				continue;
+			else {
+				error = -EINTR;
+				goto out;
+			}
 		}
 
 		if (lock_recovery_try(ls))