linux-kernel - Re: [PATCH] sched: do not call __put_task_struct() on rt if pi_blocked

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Message-ID: <20250409114330.1444221e@gandalf.local.home>
Date: Wed, 9 Apr 2025 11:43:30 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: "Luis Claudio R. Goncalves" <lgoncalv@...hat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Clark Williams
 <clrkwllms@...nel.org>, Tejun Heo <tj@...nel.org>, David Vernet
 <dvernet@...a.com>, Barret Rhoden <brho@...gle.com>, Josh Don
 <joshdon@...gle.com>, Crystal Wood <crwood@...hat.com>,
 linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev, Juri Lelli
 <juri.lelli@...hat.com>, lclaudio00@...il.com
Subject: Re: [PATCH] sched: do not call __put_task_struct() on rt if
 pi_blocked_on is set

On Tue, 8 Apr 2025 21:27:37 -0300
"Luis Claudio R. Goncalves" <lgoncalv@...hat.com> wrote:

>  {
> +	bool defer = false;
> +
>  	if (!refcount_dec_and_test(&t->usage))
>  		return;
>  
>  	/*
>  	 * In !RT, it is always safe to call __put_task_struct().
> -	 * Under RT, we can only call it in preemptible context.
> +	 * Under RT, we can only call it in preemptible context,
> +	 * when not blocked on a PI chain.
>  	 */
> -	if (!IS_ENABLED(CONFIG_PREEMPT_RT) || preemptible()) {
> +#ifdef CONFIG_PREEMPT_RT
> +	if (!preemptible() || current->pi_blocked_on)
> +		defer = true;
> +#endif

Why add the ugly #ifdef back?

	if (!IS_ENABLED(CONFIG_PREEMPT_RT) ||
	    (preemptible() && !current->pi_blocked_on)) {

-- Steve

> +
> +	if (!defer) {
>  		static DEFINE_WAIT_OVERRIDE_MAP(put_task_map, LD_WAIT_SLEEP);
>  
>