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

[Thomas Gleixner]

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?

Thanks,

        tglx