linux-kernel - Re: [PATCH v2] kernel/sched: Fix sched_fork() access an invalid sched_task

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Date:   Mon, 13 Sep 2021 08:01:00 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Zhang Qiao <zhangqiao22@...wei.com>
Cc:     mingo@...hat.com, peterz@...radead.org,
        linux-kernel@...r.kernel.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com
Subject: Re: [PATCH v2] kernel/sched: Fix sched_fork() access an invalid
 sched_task_group

Hello,

On Sat, Sep 11, 2021 at 03:50:54PM +0800, Zhang Qiao wrote:
> Between cgroup_can_fork() and cgroup_post_fork(), the cgroup
> membership is fixed and thus sched_task_group can't change. So
> call sched_fork() after cgroup_can_fork() and update the child's
> sched_task_group before it is used.

The part being fixed looks correct to me but it's difficult to for me to
assess whether the whole relocation of the sched_fork() hook doesn't change
anything else. Besides, even if we decide to relocate the sched_fork hook, I
think it'd be better to separate the two changes - one is a relatively safe
bug fix, the other is a code reorganization with possibly subtle side
effects. So, I think it'd be better to produce a patch which just fixes the
bug even if that ends up introducing another function in the flow.

Thanks.

-- 
tejun