Re: [PATCH] kernel/sched: Fix sched_fork() access an invalid sched_task_group

[Tejun Heo]

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
> > 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.

Thanks.

-- 
tejun