linux-kernel - Re: [PATCH 1/5] cgroup/cpuset: Don't call validate

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Date:   Wed, 16 Jun 2021 22:53:44 -0400
From:   Waiman Long <llong@...hat.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Shuah Khan <shuah@...nel.org>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>, Phil Auld <pauld@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>
Subject: Re: [PATCH 1/5] cgroup/cpuset: Don't call validate_change() for some
 flag changes

On 6/16/21 4:39 PM, Tejun Heo wrote:
> Hello,
>
> On Thu, Jun 03, 2021 at 05:24:12PM -0400, Waiman Long wrote:
>> The update_flag() is called with one flag bit change and without change
>> in the various cpumasks in the cpuset. Moreover, not all changes in the
>> flag bits are validated in validate_change().  In particular, the load
>> balance flag and the two spread flags are not checked there. So there
>> is no point in calling validate_change() if those flag bits change.
> The fact that it's escaping validation conditionally from caller side is
> bothersome given that the idea is to have self-contained verifier to ensure
> correctness. I'd prefer to make the validation more complete and optimized
> (ie. detect or keep track of what changed) if really necessary rather than
> escaping partially because certain conditions aren't checked.

Thanks for the comments.

You are right. I will leave out this patch. Anyway, the rests of the 
patchset don't have a strict dependency on it.

Cheers,
Longman