step_into(): move fetching ->d_inode past handle_mounts()

... and lose messing with it in __follow_mount_rcu()
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -1474,8 +1474,7 @@ EXPORT_SYMBOL(follow_down);
  * Try to skip to top of mountpoint pile in rcuwalk mode.  Fail if
  * we meet a managed dentry that would need blocking.
  */
-static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
-			       struct inode **inode)
+static bool __follow_mount_rcu(struct nameidata *nd, struct path *path)
 {
 	struct dentry *dentry = path->dentry;
 	unsigned int flags = dentry->d_flags;
@@ -1505,13 +1504,6 @@ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
 				dentry = path->dentry = mounted->mnt.mnt_root;
 				nd->state |= ND_JUMPED;
 				nd->next_seq = read_seqcount_begin(&dentry->d_seq);
-				*inode = dentry->d_inode;
-				/*
-				 * We don't need to re-check ->d_seq after this
-				 * ->d_inode read - there will be an RCU delay
-				 * between mount hash removal and ->mnt_root
-				 * becoming unpinned.
-				 */
 				flags = dentry->d_flags;
 				// makes sure that non-RCU pathwalk could reach
 				// this state.
@@ -1527,7 +1519,7 @@ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
 }
 
 static inline int handle_mounts(struct nameidata *nd, struct dentry *dentry,
-			  struct path *path, struct inode **inode)
+			  struct path *path)
 {
 	bool jumped;
 	int ret;
@@ -1536,12 +1528,7 @@ static inline int handle_mounts(struct nameidata *nd, struct dentry *dentry,
 	path->dentry = dentry;
 	if (nd->flags & LOOKUP_RCU) {
 		unsigned int seq = nd->next_seq;
-		*inode = dentry->d_inode;
-		if (read_seqcount_retry(&dentry->d_seq, seq))
-			return -ECHILD;
-		if (unlikely(!*inode))
-			return -ENOENT;
-		if (likely(__follow_mount_rcu(nd, path, inode)))
+		if (likely(__follow_mount_rcu(nd, path)))
 			return 0;
 		// *path and nd->next_seq might've been clobbered
 		path->mnt = nd->path.mnt;
@@ -1561,8 +1548,6 @@ static inline int handle_mounts(struct nameidata *nd, struct dentry *dentry,
 		dput(path->dentry);
 		if (path->mnt != nd->path.mnt)
 			mntput(path->mnt);
-	} else {
-		*inode = d_backing_inode(path->dentry);
 	}
 	return ret;
 }
@@ -1843,15 +1828,21 @@ static const char *step_into(struct nameidata *nd, int flags,
 {
 	struct path path;
 	struct inode *inode;
-	int err = handle_mounts(nd, dentry, &path, &inode);
+	int err = handle_mounts(nd, dentry, &path);
 
 	if (err < 0)
 		return ERR_PTR(err);
+	inode = path.dentry->d_inode;
 	if (likely(!d_is_symlink(path.dentry)) ||
 	   ((flags & WALK_TRAILING) && !(nd->flags & LOOKUP_FOLLOW)) ||
 	   (flags & WALK_NOFOLLOW)) {
 		/* not a symlink or should not follow */
-		if (!(nd->flags & LOOKUP_RCU)) {
+		if (nd->flags & LOOKUP_RCU) {
+			if (read_seqcount_retry(&path.dentry->d_seq, nd->next_seq))
+				return ERR_PTR(-ECHILD);
+			if (unlikely(!inode))
+				return ERR_PTR(-ENOENT);
+		} else {
 			dput(nd->path.dentry);
 			if (nd->path.mnt != path.mnt)
 				mntput(nd->path.mnt);