linux-kernel - Re: [PATCH] cgroup: fix reverse unlock sequence in cgroup_get

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Date:	Tue, 21 Jul 2009 08:34:51 -0700
From:	Paul Menage <menage@...gle.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	Zefan Li <lizf.kernel@...il.com>, Xiaotian Feng <dfeng@...hat.com>,
	lizf@...fujitsu.com, containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cgroup: fix reverse unlock sequence in cgroup_get_sb

On Tue, Jul 21, 2009 at 5:01 AM, Balbir Singh<balbir@...ux.vnet.ibm.com> wrote:
>
> lock(A)
> lock(B)
> unlock(A)
> unlock(B)
>
> Tomorrow if a unsuspecting programmer does this
>
> lock(A)
> lock(B)
> unlock(A)
>
> code block
>
> unlock(B)
>
>
> What protects code block? lock B? Is that the intention?
>

An "unsuspecting programmer" shouldn't be adding code to
multi-threaded routines without thoroughly understanding the locking.

I guess there's no harm in this patch, but as Li says, it doesn't
really change anything.

Paul
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