fix handling of nd->depth on LOOKUP_CACHED failures in try_to_unlazy*

After switching to non-RCU mode, we want nd->depth to match the number
of entries in nd->stack[] that need eventual path_put().
legitimize_links() takes care of that on failures; unfortunately,
failure exits added for LOOKUP_CACHED do not.

We could add the logics for that into those failure exits, both in
try_to_unlazy() and in try_to_unlazy_next(), but since both checks
are immediately followed by legitimize_links() and there's no calls
of legitimize_links() other than those two...  It's easier to
move the check (and required handling of nd->depth on failure) into
legitimize_links() itself.

[caught by Jens: ... and since we are zeroing ->depth here, we need
to do drop_links() first]

Fixes: 6c6ec2b0 "fs: add support for LOOKUP_CACHED"
Tested-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -630,6 +630,11 @@ static inline bool legitimize_path(struct nameidata *nd,
 static bool legitimize_links(struct nameidata *nd)
 {
 	int i;
+	if (unlikely(nd->flags & LOOKUP_CACHED)) {
+		drop_links(nd);
+		nd->depth = 0;
+		return false;
+	}
 	for (i = 0; i < nd->depth; i++) {
 		struct saved *last = nd->stack + i;
 		if (unlikely(!legitimize_path(nd, &last->link, last->seq))) {
@@ -686,8 +691,6 @@ static bool try_to_unlazy(struct nameidata *nd)
 	BUG_ON(!(nd->flags & LOOKUP_RCU));
 
 	nd->flags &= ~LOOKUP_RCU;
-	if (nd->flags & LOOKUP_CACHED)
-		goto out1;
 	if (unlikely(!legitimize_links(nd)))
 		goto out1;
 	if (unlikely(!legitimize_path(nd, &nd->path, nd->seq)))
@@ -724,8 +727,6 @@ static bool try_to_unlazy_next(struct nameidata *nd, struct dentry *dentry, unsi
 	BUG_ON(!(nd->flags & LOOKUP_RCU));
 
 	nd->flags &= ~LOOKUP_RCU;
-	if (nd->flags & LOOKUP_CACHED)
-		goto out2;
 	if (unlikely(!legitimize_links(nd)))
 		goto out2;
 	if (unlikely(!legitimize_mnt(nd->path.mnt, nd->m_seq)))