linux-kernel - Re: [RFC PATCH] sched: Do not copy user_cpus_ptr when parent is reset_on

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Message-ID: <66d8a8c9-f03b-49de-b67f-0623a796191e@redhat.com>
Date: Thu, 5 Sep 2024 10:00:36 -0400
From: Waiman Long <longman@...hat.com>
To: Phil Auld <pauld@...hat.com>
Cc: Xuewen Yan <xuewen.yan@...soc.com>, mingo@...hat.com,
 peterz@...radead.org, juri.lelli@...hat.com, vincent.guittot@...aro.org,
 dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
 mgorman@...e.de, vschneid@...hat.com, linux-kernel@...r.kernel.org,
 ke.wang@...soc.com, di.shen@...soc.com, xuewen.yan94@...il.com
Subject: Re: [RFC PATCH] sched: Do not copy user_cpus_ptr when parent is
 reset_on_fork


On 9/5/24 09:12, Phil Auld wrote:
> On Thu, Sep 05, 2024 at 08:42:33AM -0400 Waiman Long wrote:
>> On 9/5/24 05:04, Xuewen Yan wrote:
>>> Now, the task's user_cpus_ptr would dup from parent's user_cpus_ptr.
>>> It is better reset the user_cpus_ptr when parent's reset_on_fork
>>> is set.
>> According to sched(7):
>>
>>         Each thread has a reset-on-fork scheduling flag.  When this flag
>>         is set, children created by fork(2) do not inherit privileged
>>         scheduling policies.
>>
>> It can be argued what are considered privileged scheduling policies. AFAICS,
>> a restricted affinity doesn't seem to be a "privileged" scheduling policy.
>> That is my own opinion strictly from the definition point of view, I will
>> let others weigh in on that and I am OK to go either way.
>>
> I think that one could argue that clearing a restricted affinity is
> increasing the privilege and not preventing inheritence of same.
> i.e. it would be the opposite of what reset-on-fork means.
>
> I'd say NAK to this one if I had that power.

Maybe I am not clear enough in my previous mail. My position is the same 
as yours. I think this patch is not necessary. More reasons should be 
provided as to why it is right to not inherited the restricted affinity 
when reset-on-fork flag is reset.

Cheers,
Longman