d_invalidate(): unhash immediately

Once that is done, we can just hunt mountpoints down one by one;
no new mountpoints can be added from now on, so we don't need
anything tricky in finish() callback, etc.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/dcache.c

@@ -1542,78 +1542,48 @@ void shrink_dcache_for_umount(struct super_block *sb)
 	}
 }
 
-struct detach_data {
-	struct select_data select;
-	struct dentry *mountpoint;
-};
-static enum d_walk_ret detach_and_collect(void *_data, struct dentry *dentry)
+static enum d_walk_ret find_submount(void *_data, struct dentry *dentry)
 {
-	struct detach_data *data = _data;
-
+	struct dentry **victim = _data;
 	if (d_mountpoint(dentry)) {
 		__dget_dlock(dentry);
-		data->mountpoint = dentry;
+		*victim = dentry;
 		return D_WALK_QUIT;
 	}
-
-	return select_collect(&data->select, dentry);
-}
-
-static void check_and_drop(void *_data)
-{
-	struct detach_data *data = _data;
-
-	if (!data->mountpoint && list_empty(&data->select.dispose))
-		__d_drop(data->select.start);
+	return D_WALK_CONTINUE;
 }
 
 /**
  * d_invalidate - detach submounts, prune dcache, and drop
  * @dentry: dentry to invalidate (aka detach, prune and drop)
- *
- * no dcache lock.
- *
- * The final d_drop is done as an atomic operation relative to
- * rename_lock ensuring there are no races with d_set_mounted.  This
- * ensures there are no unhashed dentries on the path to a mountpoint.
  */
 void d_invalidate(struct dentry *dentry)
 {
-	/*
-	 * If it's already been dropped, return OK.
-	 */
+	bool had_submounts = false;
 	spin_lock(&dentry->d_lock);
 	if (d_unhashed(dentry)) {
 		spin_unlock(&dentry->d_lock);
 		return;
 	}
+	__d_drop(dentry);
 	spin_unlock(&dentry->d_lock);
 
 	/* Negative dentries can be dropped without further checks */
-	if (!dentry->d_inode) {
-		d_drop(dentry);
+	if (!dentry->d_inode)
 		return;
-	}
 
+	shrink_dcache_parent(dentry);
 	for (;;) {
-		struct detach_data data;
-
-		data.mountpoint = NULL;
-		INIT_LIST_HEAD(&data.select.dispose);
-		data.select.start = dentry;
-		data.select.found = 0;
-
-		d_walk(dentry, &data, detach_and_collect, check_and_drop);
-
-		if (!list_empty(&data.select.dispose))
-			shrink_dentry_list(&data.select.dispose);
-		else if (!data.mountpoint)
+		struct dentry *victim = NULL;
+		d_walk(dentry, &victim, find_submount, NULL);
+		if (!victim) {
+			if (had_submounts)
+				shrink_dcache_parent(dentry);
 			return;
-
-		if (data.mountpoint) {
-			detach_mounts(data.mountpoint);
-			dput(data.mountpoint);
 		}
+		had_submounts = true;
+		detach_mounts(victim);
+		dput(victim);
 	}
 }
 EXPORT_SYMBOL(d_invalidate);