vfs: make follow_link check RCU safe

This will allow this code to be used in RCU mode.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/namei.c b/fs/namei.c
index 41445e7fd3398d2f9140e374c716bf439b3ff210..c6b996817bb39cd6778a5c6caaf3eb92c20ae4fa 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2201,6 +2201,7 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
        int acc_mode = op->acc_mode;
        struct file *filp;
        struct inode *inode;
+       int symlink_ok = 0;
        int error;
 
        nd->flags &= ~LOOKUP_PARENT;
@@ -2232,7 +2233,6 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
        }
 
        if (!(open_flag & O_CREAT)) {
-               int symlink_ok = 0;
                if (nd->last.name[nd->last.len])
                        nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
                if (open_flag & O_PATH && !(nd->flags & LOOKUP_FOLLOW))
@@ -2364,8 +2364,16 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
        if (!inode)
                goto exit_dput;
 
-       if (inode->i_op->follow_link)
+       if (should_follow_link(inode, !symlink_ok)) {
+               if (nd->flags & LOOKUP_RCU) {
+                       if (unlikely(unlazy_walk(nd, path->dentry))) {
+                               error = -ECHILD;
+                               goto exit;
+                       }
+               }
+               BUG_ON(inode != path->dentry->d_inode);
                return NULL;
+       }
 
        path_to_nameidata(path, nd);
        nd->inode = inode;