ocfs2: Fix use after free on remount read-only

We also have to cancel quota syncing thread on remount read only because
at that moment quota is being turned off. Otherwise quota syncing thread
will try to access already freed quota structures.
Signed-off-by: Jan Kara <jack@suse.cz>

fs/ocfs2/super.c

@@ -883,9 +883,15 @@ static int ocfs2_susp_quotas(struct ocfs2_super *osb, int unsuspend)
 					sb_dqopt(sb)->files[type],
 					type, QFMT_OCFS2,
 					DQUOT_SUSPENDED);
-		else
+		else {
+			struct ocfs2_mem_dqinfo *oinfo;
+
+			/* Cancel periodic syncing before suspending */
+			oinfo = sb_dqinfo(sb, type)->dqi_priv;
+			cancel_delayed_work_sync(&oinfo->dqi_sync_work);
 			status = vfs_quota_disable(sb, type,
 						   DQUOT_SUSPENDED);
+		}
 		if (status < 0)
 			break;
 	}