follow_dotdot(): be lazy about changing nd->path

Change nd->path only after the loop is done and only in case we hadn't
ended up finding ourselves in root.  Same for NO_XDEV check.

That separates the "check how far back do we need to go through the
mount stack" logics from the rest of .. traversal.

NOTE: path_get/path_put introduced here are temporary.  They will
go away later in the series.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/namei.c b/fs/namei.c
index af18ede..9cfb709 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1748,16 +1748,24 @@ static struct dentry *follow_dotdot(struct nameidata *nd,
        if (path_equal(&nd->path, &nd->root))
                goto in_root;
        if (unlikely(nd->path.dentry == nd->path.mnt->mnt_root)) {
+               struct path path = nd->path;
+               path_get(&path);
                while (1) {
-                       if (!follow_up(&nd->path))
+                       if (!follow_up(&path)) {
+                               path_put(&path);
                                goto in_root;
-                       if (unlikely(nd->flags & LOOKUP_NO_XDEV))
-                               return ERR_PTR(-EXDEV);
-                       if (path_equal(&nd->path, &nd->root))
+                       }
+                       if (path_equal(&path, &nd->root)) {
+                               path_put(&path);
                                goto in_root;
-                       if (nd->path.dentry != nd->path.mnt->mnt_root)
+                       }
+                       if (path.dentry != nd->path.mnt->mnt_root)
                                break;
                }
+               path_put(&nd->path);
+               nd->path = path;
+               if (unlikely(nd->flags & LOOKUP_NO_XDEV))
+                       return ERR_PTR(-EXDEV);
        }
        /* rare case of legitimate dget_parent()... */
        parent = dget_parent(nd->path.dentry);