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

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Message-ID: <Z37ZVyx_PI6cHwZ7@slm.duckdns.org>
Date: Wed, 8 Jan 2025 10:00:23 -1000
From: Tejun Heo <tj@...nel.org>
To: 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

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.

-- 
tejun