gfs2: Sanitize kthread stopping

Immediately stop the logd and quotad kernel threads when a filesystem
withdraw is detected: those threads aren't doing anything useful after a
withdraw.  (Depends on the extra logd and quotad task struct references
held since commit 7a109f383fa3 ("gfs2: Fix asynchronous thread
destruction").)

In addition, check for kthread_should_stop() in the wait condition in
gfs2_quotad() to stop immediately when kthread_stop() is called.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

fs/gfs2/log.c

@@ -1298,11 +1298,9 @@ int gfs2_logd(void *data)
 	unsigned long t = 1;
 
 	while (!kthread_should_stop()) {
+		if (gfs2_withdrawn(sdp))
+			break;
 
-		if (gfs2_withdrawn(sdp)) {
-			msleep_interruptible(HZ);
-			continue;
-		}
 		/* Check for errors writing to the journal */
 		if (sdp->sd_log_error) {
 			gfs2_lm(sdp,
@@ -1311,7 +1309,7 @@ int gfs2_logd(void *data)
 				"prevent further damage.\n",
 				sdp->sd_fsname, sdp->sd_log_error);
 			gfs2_withdraw(sdp);
-			continue;
+			break;
 		}
 
 		if (gfs2_jrnl_flush_reqd(sdp) || t == 0) {
@@ -1339,6 +1337,7 @@ int gfs2_logd(void *data)
 				gfs2_ail_flush_reqd(sdp) ||
 				gfs2_jrnl_flush_reqd(sdp) ||
 				sdp->sd_log_error ||
+				gfs2_withdrawn(sdp) ||
 				kthread_should_stop(),
 				t);
 	}

fs/gfs2/quota.c

@@ -1559,9 +1559,9 @@ int gfs2_quotad(void *data)
 	unsigned long t = 0;
 
 	while (!kthread_should_stop()) {
-
 		if (gfs2_withdrawn(sdp))
-			goto bypass;
+			break;
+
 		/* Update the master statfs file */
 		if (sdp->sd_statfs_force_sync) {
 			int error = gfs2_statfs_sync(sdp->sd_vfs, 0);
@@ -1579,11 +1579,12 @@ int gfs2_quotad(void *data)
 
 		try_to_freeze();
 
-bypass:
 		t = min(quotad_timeo, statfs_timeo);
 
 		t = wait_event_interruptible_timeout(sdp->sd_quota_wait,
-				sdp->sd_statfs_force_sync,
+				sdp->sd_statfs_force_sync ||
+				gfs2_withdrawn(sdp) ||
+				kthread_should_stop(),
 				t);
 
 		if (sdp->sd_statfs_force_sync)