linux-kernel - Re: [patch 03/63] sched: Prepare for RT sleeping spin/rwlocks

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Message-ID: <YQlYB7wE8HaDjyd7@hirez.programming.kicks-ass.net>
Date:   Tue, 3 Aug 2021 16:51:51 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Mike Galbraith <efault@....de>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Davidlohr Bueso <dave@...olabs.net>
Subject: Re: [patch 03/63] sched: Prepare for RT sleeping spin/rwlocks

On Tue, Aug 03, 2021 at 04:04:07PM +0200, Thomas Gleixner wrote:
> On Tue, Aug 03 2021 at 11:48, Peter Zijlstra wrote:
> 
> > On Sun, Aug 01, 2021 at 05:30:06PM +0200, Mike Galbraith wrote:
> >> On Fri, 2021-07-30 at 15:50 +0200, Thomas Gleixner wrote:
> >> > 
> >> > --- a/include/linux/sched.h
> >> > +++ b/include/linux/sched.h
> >> > @@ -155,6 +155,27 @@ struct task_group;
> >> >                 WRITE_ONCE(current->__state, (state_value));            \
> >> >                 raw_spin_unlock_irqrestore(&current->pi_lock, flags);   \
> >> >         } while (0)
> >> > +
> >> > +
> >> > +#define current_save_and_set_rtlock_wait_state()                       \
> >> > +       do {                                                            \
> >> > +               raw_spin_lock(&current->pi_lock);                       \
> >
> > That wants to be irqsafe methinks, I realize this is PREEMPT_RT only and
> > there the _irqfoo crap is a no-op so this doesn't really matter one way
> > or the other, but still, taking PI lock without IRQ disable makes my
> > head go BUG-BUG-BUG :-)
> 
> Actually the rule to lock PI lock irqsave still persists on RT, but this
> has to be called with interrupts disabled (rtmutex::wait_lock is held),
> so adding a lockdep_assert_irqs_disable() might be good enough to spare
> the extra save/restore. Hmm?

Works for me.. and yes, duh, raw_.