linux-kernel - Re: [PATCH v2] cgroup/cpuset: remove kernfs active break

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Message-ID: <6fb6d82f-a321-4b29-9fd6-60f7a8758233@redhat.com>
Date: Wed, 8 Jan 2025 15:04:39 -0500
From: Waiman Long <llong@...hat.com>
To: Tejun Heo <tj@...nel.org>, Waiman Long <llong@...hat.com>
Cc: Chen Ridong <chenridong@...weicloud.com>, hannes@...xchg.org,
 mkoutny@...e.com, cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] cgroup/cpuset: remove kernfs active break


On 1/8/25 3:00 PM, Tejun Heo wrote:
> Hello,
>
> On Wed, Jan 08, 2025 at 02:50:19PM -0500, Waiman Long wrote:
> ...
>> It is not the strict ordering that I am worrying about. It is all about the
>> possibility of hitting some race conditions.
>>
>> I am thinking of a scenario where a cpuset loses all its CPUs in hotunplug
>> and then restored by adding other CPUs. There is chance that the css will be
>> operated on concurrently by the auto-transfer task and another task moving
>> new task to the css. I am not sure if that will be a problem or not. Anyway,
>> it is very rare that we will be in such a situation.
> Hmm... I might be missing something but cgroup_transfer_tasks() is fully
> synchronized against migrations. I don't see anything dangerous there.
>
> Thanks.

I probably misread some of the code. Then it is not an issue anymore.

Thanks,
Longman