On Mon, Nov 19, 2012 at 04:08:04PM +0800, Li Zefan wrote:

quoted

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 0f8fa6a..d0803f0 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c

@@ -2684,9 +2684,7 @@ static int cgroup_create_dir(struct cgroup *cgrp, struct dentry *dentry,
 		dentry->d_fsdata = cgrp;
 		inc_nlink(parent->d_inode);
 		rcu_assign_pointer(cgrp->dentry, dentry);
-		dget(dentry);
 	}
-	dput(dentry);
 

The code has been there since cgroup was merged into mainline!

I know.  Sometimes it's scary how many latent bugs we have in the
kernel and how long many of them have been around.  At other times,
it's comforting.  I mean, there's a pretty good chance that other
people don't notice my screw ups, right?  :P

-- 
tejun