make nameidata_dentry_drop_rcu_maybe() always leave RCU mode

Now we have do_follow_link() guaranteed to leave without dangling RCU
and the next step will get LOOKUP_RCU logics completely out of
link_path_walk().

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

1 files changed, 11 insertions, 5 deletions

diff --git a/fs/namei.c b/fs/namei.c
index ea14bfb04785..53bba7c1a520 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -498,8 +498,15 @@ err_root:
 /* Try to drop out of rcu-walk mode if we were in it, otherwise do nothing.  */
 static inline int nameidata_dentry_drop_rcu_maybe(struct nameidata *nd, struct dentry *dentry)
 {
-        if (nd->flags & LOOKUP_RCU)
-                return nameidata_dentry_drop_rcu(nd, dentry);
+        if (nd->flags & LOOKUP_RCU) {
+                if (unlikely(nameidata_dentry_drop_rcu(nd, dentry))) {
+                        nd->flags &= ~LOOKUP_RCU;
+                        nd->root.mnt = NULL;
+                        rcu_read_unlock();
+                        br_read_unlock(vfsmount_lock);
+                        return -ECHILD;
+                }
+        }
         return 0;
 }
 
@@ -1424,7 +1431,7 @@ static int link_path_walk(const char *name, struct nameidata *nd)
                 if (inode && inode->i_op->follow_link) {
                         err = do_follow_link(inode, &next, nd);
                         if (err)
-                                goto return_err;
+                                return err;
                         nd->inode = nd->path.dentry->d_inode;
                 } else {
                         path_to_nameidata(&next, nd);
@@ -1455,7 +1462,7 @@ last_component:
                     (lookup_flags & LOOKUP_FOLLOW)) {
                         err = do_follow_link(inode, &next, nd);
                         if (err)
-                                goto return_err;
+                                return err;
                         nd->inode = nd->path.dentry->d_inode;
                 } else {
                         path_to_nameidata(&next, nd);
@@ -1477,7 +1484,6 @@ lookup_parent:
         }
         if (!(nd->flags & LOOKUP_RCU))
                 path_put(&nd->path);
-return_err:
         if (nd->flags & LOOKUP_RCU) {
                 nd->flags &= ~LOOKUP_RCU;
                 nd->root.mnt = NULL;