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

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Message-ID: <20250409123944.15df8714@gandalf.local.home>
Date: Wed, 9 Apr 2025 12:39:44 -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>
Subject: Re: [PATCH] sched: do not call __put_task_struct() on rt if
 pi_blocked_on is set

On Wed, 9 Apr 2025 13:27:12 -0300
"Luis Claudio R. Goncalves" <lgoncalv@...hat.com> wrote:

> > > -	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)) {  
> 
> I had to add the #ifdef to avoid the build failing if CONFIG_RT_MUTEXES is
> not set. I do know SMP, FUTEX, I2C, PSTORE and a few more things depend on
> CONFIG_RT_MUTEXES being enabled, but I opted for being thorough.
> 
> I would be more than glad getting rid of the #ifdef and simplifying the patch
> if that possible build failure is not a case to worry about, if RT_MUTEXES are
> always enabled nowadays.
> 

Because pi_blocked_on is only defined when CONFIG_RT_MUTEXES is enabled?

OK, then perhaps we should add in sched.h:

#ifdef CONFIG_RT_MUTEXES
static inline bool tsk_is_pi_blocked_on(struct task_struct *tsk)
{
	return tsk->pi_blocked_on != NULL;
}
#else
static inline bool tsk_is_pi_blocked_on(strut task_struct *tsk)
{
	return false;
}
#endif

??

-- Steve