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 19:54:26 -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 16:50, Tejun Heo wrote:
> On Thu, Feb 02, 2023 at 04:05:14PM -0500, Waiman Long wrote:
>> 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.
> Neither patch looks like they would break anything. That said, the patches
> aren't trivial and we're really close to the merge window, so I'd really
> appreciate if you can take a look and test a bit before we send these
> Linus's way. We can replace it with a better solution afterwards.

OK, will do.

Cheers,
Longman