linux-kernel - Re: [PATCH v5 1/2] cgroup: fix cgroup

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Date:	Mon, 4 Mar 2013 09:50:32 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Li Zefan <lizefan@...wei.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	cgroups <cgroups@...r.kernel.org>
Subject: Re: [PATCH v5 1/2] cgroup: fix cgroup_path() vs rename() race

On Fri, Mar 01, 2013 at 03:01:56PM +0800, Li Zefan wrote:
> rename() will change dentry->d_name. The result of this race can
> be worse than seeing partially rewritten name, but we might access
> a stale pointer because rename() will re-allocate memory to hold
> a longer name.
> 
> As accessing dentry->name must be protected by dentry->d_lock or
> parent inode's i_mutex, while on the other hand cgroup-path() can
> be called with some irq-safe spinlocks held, we can't generate
> cgroup path using dentry->d_name.
> 
> Alternatively we make a copy of dentry->d_name and save it in
> cgrp->name when a cgroup is created, and update cgrp->name at
> rename().
> 
> v5: use flexible array instead of zero-size array.
> v4: - allocate root_cgroup_name and all root_cgroup->name points to it.
>     - add cgroup_name() wrapper.
> v3: use kfree_rcu() instead of synchronize_rcu() in user-visible path.
> v2: make cgrp->name RCU safe.
> 
> Signed-off-by: Li Zefan <lizefan@...wei.com>

Applied 1-2 to cgroup/for-3.10.

Thanks.

-- 
tejun
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