gfs2: fix infinite loop in gfs2_ail1_flush on io error

Before this patch, an IO error encountered in function gfs2_ail1_flush
would cause a deadlock: because of the io error (and its resulting
withdrawn state), buffers stopped being written to the journal.
Buffers would remain on the ail1 list, so gfs2_ail1_start_one would
return 1 to indicate dirty buffers were still on the ail1 list.
However, when function gfs2_ail1_flush got a non-zero return code,
it would goto restart to retry the writes, which meant it would never
finish, and thus the infinite loop.
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

fs/gfs2/log.c

@@ -161,7 +161,8 @@ void gfs2_ail1_flush(struct gfs2_sbd *sdp, struct writeback_control *wbc)
 	list_for_each_entry_reverse(tr, head, tr_list) {
 		if (wbc->nr_to_write <= 0)
 			break;
-		if (gfs2_ail1_start_one(sdp, wbc, tr, &withdraw))
+		if (gfs2_ail1_start_one(sdp, wbc, tr, &withdraw) &&
+		    !gfs2_withdrawn(sdp))
 			goto restart;
 	}
 	spin_unlock(&sdp->sd_ail_lock);