__d_unalias() should refuse to move mountpoints

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

diff --git a/fs/dcache.c b/fs/dcache.c
index 015586f1ffc6061a20b05320ed335a33757f3255..8086636bf796ab328219d4a898608af1be2fdb2b 100644 (file)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2387,14 +2387,13 @@ static struct dentry *__d_unalias(struct inode *inode,
                struct dentry *dentry, struct dentry *alias)
 {
        struct mutex *m1 = NULL, *m2 = NULL;
-       struct dentry *ret;
+       struct dentry *ret = ERR_PTR(-EBUSY);
 
        /* If alias and dentry share a parent, then no extra locks required */
        if (alias->d_parent == dentry->d_parent)
                goto out_unalias;
 
        /* See lock_rename() */
-       ret = ERR_PTR(-EBUSY);
        if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex))
                goto out_err;
        m1 = &dentry->d_sb->s_vfs_rename_mutex;
@@ -2402,8 +2401,10 @@ static struct dentry *__d_unalias(struct inode *inode,
                goto out_err;
        m2 = &alias->d_parent->d_inode->i_mutex;
 out_unalias:
-       __d_move(alias, dentry);
-       ret = alias;
+       if (likely(!d_mountpoint(alias))) {
+               __d_move(alias, dentry);
+               ret = alias;
+       }
 out_err:
        spin_unlock(&inode->i_lock);
        if (m2)