linux-kernel - Re: [PATCH -next] cpuset: add cpuset1_online

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Message-ID: <5a35692f-2800-4fd4-9c23-97d0284293df@redhat.com>
Date: Tue, 16 Dec 2025 09:58:02 -0500
From: Waiman Long <llong@...hat.com>
To: Michal Koutný <mkoutny@...e.com>,
 Chen Ridong <chenridong@...weicloud.com>
Cc: tj@...nel.org, hannes@...xchg.org, cgroups@...r.kernel.org,
 linux-kernel@...r.kernel.org, lujialin4@...wei.com
Subject: Re: [PATCH -next] cpuset: add cpuset1_online_css helper for
 v1-specific operations

On 12/16/25 9:03 AM, Michal Koutný wrote:
> On Tue, Dec 16, 2025 at 08:13:53PM +0800, Chen Ridong <chenridong@...weicloud.com> wrote:
>> Regarding the lock assertions: cpuset_mutex is defined in cpuset.c and is not visible in
>> cpuset-v1.c. Given that cpuset v1 is deprecated, would you prefer that we add a helper to assert
>> cpuset_mutex is locked? Is that worth?
> It could be un-static'd and defined in cpuset-internal.h. (Hopefully, we
> should not end up with random callers of the helper but it's IMO worth
> it for docs and greater safety.)
I would suggest defining a "assert_cpuset_lock_held(void)" helper 
function and put the declaration in include/linux/cpuset.h together with 
cpuset_lock/unlock() to complete the full set. This will allow other 
kernel subsystems to acquire the cpuset_mutex and assert that the mutex 
was held.
>
>> Should we guard with !cpuset_v2() or !is_in_v2mode()?
>>
>> In cgroup v1, if the cpuset is operating in v2 mode, are these flags still valid?
> I have no experience with this transitional option so that made me look
> at the docs and there we specify it only affects behaviors of CPU masks,
> not the extra flags. So I wanted to suggest !cpuset_v2(), correct?

The "cpuset_v2_mode" mount flag is used for making the behavior of 
cpuset.{cpus,mems}.effective in v1 behave like in v2. It has no effect 
on other v1 specific control files. So cpuset1_online_css() should only 
be called if "!cpuset_v2()".

Cheers,
Longman

>
> Thanks,
> Michal