Re: [PATCH -next] cpuset: add cpuset1_online_css helper for v1-specific operations

[Chen Ridong <chenridong@huaweicloud.com>]

On 2025/12/16 22:58, Waiman Long wrote:
> On 12/16/25 9:03 AM, Michal Koutný wrote:
>> On Tue, Dec 16, 2025 at 08:13:53PM +0800, Chen Ridong <chenridong@huaweicloud.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.

Considering potential use by other subsystems, this is worthwhile. I will add the helper.

>>
>>> 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()".
> 

If cpuset1_online_css() is only called under the condition !cpuset_v2(), a compile-time option might
suffice? When CONFIG_CPUSETS_V1=n, cpuset1_online_css could be defined as an empty inline function.

-- 
Best regards,
Ridong