Re: [PATCH 04/31] sched: Allow sched_cgroup_fork() to fail and introduce sched_cancel_fork()

[Tejun Heo]

On Mon, Dec 12, 2022 at 12:13:31PM +0100, Peter Zijlstra wrote:
> On Tue, Nov 29, 2022 at 10:22:46PM -1000, Tejun Heo wrote:
> > A new sched_clas needs a bit more control over forking. This patch makes the
>                  ^
>                  (insufficient s's)

Will update.

> > following changes:
> > 
> > * Add sched_cancel_fork() which is called if fork fails after sched_fork()
> >   succeeds so that the preparation can be undone.
> > 
> > * Allow sched_cgroup_fork() to fail.
> > 
> > Neither is used yet and this patch shouldn't cause any behavior changes.
> 
> Fails to explain why this would be needed and why that would be a good
> thing. IOW, total lack of justification.

This is because sched_ext calls out to BPF scheduler's prepare_enable()
operation to prepare the task. The operation is allowed to fail (e.g. it
might need to allocate something which can fail), so we need a way back back
out of it.

Thanks.

-- 
tejun