linux-kernel - Re: [PATCH 1/2] cpuset: Fix cpuset_cpus_allowed() to not filter offline CPUs

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Date:   Thu, 2 Feb 2023 16:05:14 -0500
From:   Waiman Long <longman@...hat.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        kernel-team@...roid.com, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>, cgroups@...r.kernel.org
Subject: Re: [PATCH 1/2] cpuset: Fix cpuset_cpus_allowed() to not filter
 offline CPUs


On 2/2/23 15:53, Waiman Long wrote:
>
> On 2/2/23 15:48, Tejun Heo wrote:
>> On Thu, Feb 02, 2023 at 03:46:02PM -0500, Waiman Long wrote:
>>>>> I will work on a patchset to do that as a counter offer.
>>>> We will need a small and simple patch for /urgent, or I will need to
>>>> revert all your patches -- your call.
>>>>
>>>> I also don't tihnk you fully appreciate the ramifications of
>>>> task_cpu_possible_mask(), cpuset currently gets that quite wrong.
>>> OK, I don't realize the urgency of that. If it is that urgent, I 
>>> will have
>>> no objection to get it in for now. We can improve it later on. So 
>>> are you
>>> planning to get it into the current 6.2 rc or 6.3?
>>>
>>> Tejun, are you OK with that as you are the cgroup maintainer?
>> Yeah, gotta fix the regression but is there currently a solution 
>> which fixes
>> the regression but doesn't further break other stuff?
>
> I believe there is a better way to do that, but it will need more time 
> to flex out. Since cpuset_cpus_allowed() is only used by 
> kernel/sched/core.c, Peter will be responsible if it somehow breaks 
> other stuff.

Maybe my cpuset patch that don't update task's cpumask on cpu offline 
event can help. However, I don't know the exact scenario where the 
regression happen, so it may not.

Cheers,
Longman