fsnotify: fix false positive warning on inode delete

When inode is getting deleted and someone else holds reference to a mark
attached to the inode, we just detach the connector from the inode. In
that case fsnotify_put_mark() called from fsnotify_destroy_marks() will
decide to recalculate mask for the inode and __fsnotify_recalc_mask()
will WARN about invalid connector type:

WARNING: CPU: 1 PID: 12015 at fs/notify/mark.c:139
__fsnotify_recalc_mask+0x2d7/0x350 fs/notify/mark.c:139

Actually there's no reason to warn about detached connector in
__fsnotify_recalc_mask() so just silently skip updating the mask in such
case.

Reported-by: syzbot+c34692a51b9a6ca93540@syzkaller.appspotmail.com
Fixes: 3ac70bfc ("fsnotify: add helper to get mask from connector")
Signed-off-by: Jan Kara <jack@suse.cz>

fs/notify/mark.c

@@ -132,13 +132,13 @@ static void __fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
 	struct fsnotify_mark *mark;
 
 	assert_spin_locked(&conn->lock);
+	/* We can get detached connector here when inode is getting unlinked. */
+	if (!fsnotify_valid_obj_type(conn->type))
+		return;
 	hlist_for_each_entry(mark, &conn->list, obj_list) {
 		if (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)
 			new_mask |= mark->mask;
 	}
-	if (WARN_ON(!fsnotify_valid_obj_type(conn->type)))
-		return;
-
 	*fsnotify_conn_mask_p(conn) = new_mask;
 }