linux-kernel - Re: [PATCH 3/4] cpuset: Fix unchecked calls to NODEMASK

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Message-ID: <AANLkTin6TqQMHSpQjNXNrgGAHG8DL6CvzhTm3KHoxv0y@mail.gmail.com>
Date:	Thu, 17 Feb 2011 15:50:01 -0800
From:	Paul Menage <menage@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Li Zefan <lizf@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	David Rientjes <rientjes@...gle.com>,
	缪 勰 <miaox@...fujitsu.com>,
	linux-mm@...ck.org
Subject: Re: [PATCH 3/4] cpuset: Fix unchecked calls to NODEMASK_ALLOC()

On Thu, Feb 17, 2011 at 2:46 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Thu, 17 Feb 2011 09:50:09 +0800
> Li Zefan <lizf@...fujitsu.com> wrote:
>
>> +/*
>> + * In functions that can't propogate errno to users, to avoid declaring a
>> + * nodemask_t variable, and avoid using NODEMASK_ALLOC that can return
>> + * -ENOMEM, we use this global cpuset_mems.
>> + *
>> + * It should be used with cgroup_lock held.
>
> I'll do s/should/must/ - that would be a nasty bug.
>
> I'd be more comfortable about the maintainability of this optimisation
> if we had
>
>        WARN_ON(!cgroup_is_locked());
>
> at each site.
>

Agreed - that was my first thought on reading the patch. How about:

static nodemask_t *cpuset_static_nodemask() {
  static nodemask_t nodemask;
  WARN_ON(!cgroup_is_locked());
  return &nodemask;
}

and then just call cpuset_static_nodemask() in the various locations
being patched?

Paul
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