Re: [PATCH v5 7/9] sched/fair: allow changing cgroup of new forked task

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Aug 18, 2022 at 11:43:41AM +0800, Chengming Zhou wrote:

> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 8e3f1c3f0b2c..157f7461a08a 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4550,11 +4550,11 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
>  {
>  	__sched_fork(clone_flags, p);
>  	/*
> -	 * We mark the process as NEW here. This guarantees that
> +	 * We mark the process as running here. This guarantees that
>  	 * nobody will actually run it, and a signal or other external
>  	 * event cannot wake it up and insert it on the runqueue either.
>  	 */
> -	p->__state = TASK_NEW;
> +	p->__state = TASK_RUNNING;
>  
>  	/*
>  	 * Make sure we do not leak PI boosting priority to the child.
> @@ -4672,7 +4672,6 @@ void wake_up_new_task(struct task_struct *p)
>  	struct rq *rq;
>  
>  	raw_spin_lock_irqsave(&p->pi_lock, rf.flags);
> -	WRITE_ONCE(p->__state, TASK_RUNNING);
>  #ifdef CONFIG_SMP
>  	/*
>  	 * Fork balancing, do it here and not earlier because:
> @@ -10290,36 +10289,19 @@ static void cpu_cgroup_css_free(struct cgroup_subsys_state *css)
>  	sched_unregister_group(tg);
>  }

> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index eba8a64f905a..e0d34ecdabae 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -11840,6 +11840,13 @@ void init_cfs_rq(struct cfs_rq *cfs_rq)
>  #ifdef CONFIG_FAIR_GROUP_SCHED
>  static void task_change_group_fair(struct task_struct *p)
>  {
> +	/*
> +	 * We couldn't detach or attach a forked task which
> +	 * hasn't been woken up by wake_up_new_task().
> +	 */
> +	if (!p->on_rq && !p->se.sum_exec_runtime)
> +		return;
> +
>  	detach_task_cfs_rq(p);

Wouldn't that be much clearer when expressed in TASK_NEW ?