lookup_fast(): don't bother with inode

Note that validation of ->d_seq after ->d_inode fetch is gone, along
with fetching of ->d_inode itself.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -1621,8 +1621,7 @@ static struct dentry *__lookup_hash(const struct qstr *name,
 	return dentry;
 }
 
-static struct dentry *lookup_fast(struct nameidata *nd,
-				  struct inode **inode)
+static struct dentry *lookup_fast(struct nameidata *nd)
 {
 	struct dentry *dentry, *parent = nd->path.dentry;
 	int status = 1;
@@ -1640,22 +1639,11 @@ static struct dentry *lookup_fast(struct nameidata *nd,
 			return NULL;
 		}
 
-		/*
-		 * This sequence count validates that the inode matches
-		 * the dentry name information from lookup.
-		 */
-		*inode = d_backing_inode(dentry);
-		if (read_seqcount_retry(&dentry->d_seq, nd->next_seq))
-			return ERR_PTR(-ECHILD);
-
 		/*
 		 * This sequence count validates that the parent had no
 		 * changes while we did the lookup of the dentry above.
-		 *
-		 * The memory barrier in read_seqcount_begin of child is
-		 *  enough, we can use __read_seqcount_retry here.
 		 */
-		if (__read_seqcount_retry(&parent->d_seq, nd->seq))
+		if (read_seqcount_retry(&parent->d_seq, nd->seq))
 			return ERR_PTR(-ECHILD);
 
 		status = d_revalidate(dentry, nd->flags);
@@ -1997,7 +1985,6 @@ static const char *handle_dots(struct nameidata *nd, int type)
 static const char *walk_component(struct nameidata *nd, int flags)
 {
 	struct dentry *dentry;
-	struct inode *inode;
 	/*
 	 * "." and ".." are special - ".." especially so because it has
 	 * to be able to know about the current root directory and
@@ -2008,7 +1995,7 @@ static const char *walk_component(struct nameidata *nd, int flags)
 			put_link(nd);
 		return handle_dots(nd, nd->last_type);
 	}
-	dentry = lookup_fast(nd, &inode);
+	dentry = lookup_fast(nd);
 	if (IS_ERR(dentry))
 		return ERR_CAST(dentry);
 	if (unlikely(!dentry)) {
@@ -3396,7 +3383,6 @@ static const char *open_last_lookups(struct nameidata *nd,
 	struct dentry *dir = nd->path.dentry;
 	int open_flag = op->open_flag;
 	bool got_write = false;
-	struct inode *inode;
 	struct dentry *dentry;
 	const char *res;
 
@@ -3412,7 +3398,7 @@ static const char *open_last_lookups(struct nameidata *nd,
 		if (nd->last.name[nd->last.len])
 			nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
 		/* we _can_ be in RCU mode here */
-		dentry = lookup_fast(nd, &inode);
+		dentry = lookup_fast(nd);
 		if (IS_ERR(dentry))
 			return ERR_CAST(dentry);
 		if (likely(dentry))