[DLM] fix stopping unstarted recovery

Red Hat BZ 211914

When many nodes are joining a lockspace simultaneously, the dlm gets a
quick sequence of stop/start events, a pair for adding each node.
dlm_controld in user space sends dlm_recoverd in the kernel each stop and
start event.  dlm_controld will sometimes send the stop before
dlm_recoverd has had a chance to take up the previously queued start.  The
stop aborts the processing of the previous start by setting the
RECOVERY_STOP flag.  dlm_recoverd is erroneously clearing this flag and
ignoring the stop/abort if it happens to take up the start after the stop
meant to abort it.  The fix is to check the sequence number that's
incremented for each stop/start before clearing the flag.

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

fs/dlm/recoverd.c

@@ -219,14 +219,19 @@ static int ls_recover(struct dlm_ls *ls, struct dlm_recover *rv)
 	return error;
 }
 
+/* The dlm_ls_start() that created the rv we take here may already have been
+   stopped via dlm_ls_stop(); in that case we need to leave the RECOVERY_STOP
+   flag set. */
+
 static void do_ls_recovery(struct dlm_ls *ls)
 {
 	struct dlm_recover *rv = NULL;
 
 	spin_lock(&ls->ls_recover_lock);
 	rv = ls->ls_recover_args;
 	ls->ls_recover_args = NULL;
-	clear_bit(LSFL_RECOVERY_STOP, &ls->ls_flags);
+	if (rv && ls->ls_recover_seq == rv->seq)
+		clear_bit(LSFL_RECOVERY_STOP, &ls->ls_flags);
 	spin_unlock(&ls->ls_recover_lock);
 
 	if (rv) {