[RFC][PATCH v3 52/55] follow_dotdot(): be lazy about changing nd->path

Al Viro
2020-03-01T21:53:23Z

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>
---
fs/namei.c | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index fe49db1df8ae..ab17f7ea8c9f 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1750,16 +1750,24 @@ 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);
--
2.11.0