fix oops in fs/9p late mount failure

if 9P ->get_sb() fails late (at root inode or root dentry
allocation), we'll hit its ->kill_sb() with NULL ->s_root

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

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/9p/vfs_super.c b/fs/9p/vfs_super.c
index 14a86448572c..69357c0d9899 100644
--- a/fs/9p/vfs_super.c
+++ b/fs/9p/vfs_super.c
@@ -188,7 +188,8 @@ static void v9fs_kill_super(struct super_block *s)
 
         P9_DPRINTK(P9_DEBUG_VFS, " %p\n", s);
 
-        v9fs_dentry_release(s->s_root); /* clunk root */
+        if (s->s_root)
+                v9fs_dentry_release(s->s_root); /* clunk root */
 
         kill_anon_super(s);