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Subject: Re: [PATCH] kernel/sched: Fix sched_fork() access an invalid
 sched_task_group
To:     Tejun Heo <tj@kernel.org>
CC:     <peterz@infradead.org>, <juri.lelli@redhat.com>,
        <linux-kernel@vger.kernel.org>, <mingo@redhat.com>,
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References: <20210826112635.7404-1-zhangqiao22@huawei.com>
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From:   Zhang Qiao <zhangqiao22@huawei.com>
Message-ID: <128d52ab-b4ee-65f8-e0a3-2796ef43a98b@huawei.com>
Date:   Wed, 1 Sep 2021 15:43:00 +0800
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hello,tejun.

?? 2021/9/1 6:59, Tejun Heo д??:
> Hello,
> 
> On Tue, Aug 31, 2021 at 03:58:42PM +0800, Zhang Qiao wrote:
>>> I think this would allow cgroup migrations to take place before
>>> sched_post_fork() is run, which likely will break stuff. The right

cgroup migrations? Do you mean child process set its cgroups at
cgroup_subsys->fork()?

>>> thing to do likely is taking sched_task_group (and whatever other
>>> fields) after cgroup_can_fork(), which fixates the cgroup memberships,
>>
>> But it still seems possible that it accessed an invalid sched_task_group?
>> because the child process does not update its sched_task_group util
>> cgroup_post_fork().
> 
> Between cgroup_can_fork() and cgroup_post_fork(), the cgroup membership and
> thus sched_task_group can't change, so if the child sets it to the parent's
> inbetween, the sched_task_group can't go away.

so the child just need to update its sched_task_group after cgroup_can_fork(),
then call sched_fork(), is it right?

thanks.

--
Qiao Zhang.
> 
> Thanks.
>