linux-kernel - Re: [PATCH] freezer,sched: Rewrite core freezer logic

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Date:   Fri, 11 Jun 2021 10:46:14 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     rjw@...ysocki.net, Oleg Nesterov <oleg@...hat.com>,
        mingo@...nel.org, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, mgorman@...e.de,
        Will Deacon <will@...nel.org>
Cc:     Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH] freezer,sched: Rewrite core freezer logic

On Fri, Jun 11, 2021 at 10:45:00AM +0200, Peter Zijlstra wrote:
> @@ -52,41 +52,67 @@ bool freezing_slow_path(struct task_stru
>  }
>  EXPORT_SYMBOL(freezing_slow_path);
>  
> +/* Recursion relies on tail-call optimization to not blow away the stack */
> +static bool __frozen(struct task_struct *p)
> +{
> +	if (p->state == TASK_FROZEN)
> +		return true;
> +
> +	/*
> +	 * If stuck in TRACED, and the ptracer is FROZEN, we're frozen too.
> +	 */
> +	if (task_is_traced(p))
> +		return frozen(rcu_dereference(p->parent));
> +
> +	/*
> +	 * If stuck in STOPPED and the parent is FROZEN, we're frozen too.
> +	 */
> +	if (task_is_stopped(p))
> +		return frozen(rcu_dereference(p->real_parent));
> +
> +	return false;
> +}
> +
> +bool frozen(struct task_struct *p)
> +{
> +	bool ret;
> +
> +	rcu_read_lock();
> +	ret = __frozen(p);
> +	rcu_read_unlock();
> +
> +	return ret;
> +}

Oleg, this bit in particular we'd like some feedback on, if possible.

Thanks!