linux-kernel - Re: [RESEND PATCH v3] cpuset: restore sanity to cpuset_cpus_allowed

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Message-ID: <20190612160244.GP3341036@devbig004.ftw2.facebook.com>
Date:   Wed, 12 Jun 2019 09:02:44 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Joel Savitz <jsavitz@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Li Zefan <lizefan@...wei.com>,
        Phil Auld <pauld@...hat.com>, Waiman Long <longman@...hat.com>,
        Michal Koutný <mkoutny@...e.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, cgroups@...r.kernel.org
Subject: Re: [RESEND PATCH v3] cpuset: restore sanity to
 cpuset_cpus_allowed_fallback()

On Wed, Jun 12, 2019 at 11:50:48AM -0400, Joel Savitz wrote:
> In the case that a process is constrained by taskset(1) (i.e.
> sched_setaffinity(2)) to a subset of available cpus, and all of those are
> subsequently offlined, the scheduler will set tsk->cpus_allowed to
> the current value of task_cs(tsk)->effective_cpus.
> 
> This is done via a call to do_set_cpus_allowed() in the context of 
> cpuset_cpus_allowed_fallback() made by the scheduler when this case is
> detected. This is the only call made to cpuset_cpus_allowed_fallback()
> in the latest mainline kernel.
> 
> However, this is not sane behavior.

While not perfect (we'll need to stop updating task's cpumask from
cpuset to make), this is still a signifcant improvement.

 Acked-by: Tejun Heo <tj@...nel.org>

If there's no objection, I'll route it through the cgroup tree.

Thanks.

-- 
tejun