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

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Message-ID: <Z_aoIY7GwPFUqMNb@uudg.org>
Date: Wed, 9 Apr 2025 14:02:25 -0300
From: "Luis Claudio R. Goncalves" <lgoncalv@...hat.com>
To: Steven Rostedt <rostedt@...dmis.org>
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, Apr 09, 2025 at 12:39:44PM -0400, Steven Rostedt wrote:
> 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
> 
> ??

Thank you for the suggestion! I will rework the patch with that and send v2
after basic testing.

Luis
 
> -- Steve
> 
---end quoted text---