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

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Date:	Tue, 21 Jul 2009 21:17:11 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Paul Menage <menage@...gle.com>
Cc:	containers@...ts.linux-foundation.org,
	Zefan Li <lizf.kernel@...il.com>, linux-kernel@...r.kernel.org,
	Xiaotian Feng <dfeng@...hat.com>
Subject: Re: [PATCH] cgroup: fix reverse unlock sequence in cgroup_get_sb

* menage@...gle.com <menage@...gle.com> [2009-07-21 08:34:51]:

> 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.
> 

Agreed, but why leave behind places for people to do so. There is the
consistency factor as well, see below.


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

Well all the other places do it right in the same routine. 

-- 
	Balbir
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