linux-kernel - Re: [tip: locking/core] lockdep: Annotate irq

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Date:   Sat, 21 Mar 2020 19:12:49 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        x86 <x86@...nel.org>
Subject: Re: [tip: locking/core] lockdep: Annotate irq_work

On 2020-03-21 17:40:58 [+0100], Frederic Weisbecker wrote:
> > diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h
> > index 9c17f9c..f23f540 100644
> > --- a/include/linux/irqflags.h
> > +++ b/include/linux/irqflags.h
> > @@ -69,6 +69,17 @@ do {						\
> >  			current->irq_config = 0;	\
> >  	  } while (0)
> >  
> > +# define lockdep_irq_work_enter(__work)					\
> > +	  do {								\
> > +		  if (!(atomic_read(&__work->flags) & IRQ_WORK_HARD_IRQ))\
> > +			current->irq_config = 1;			\
> 
> So, irq_config == 1 means we are in a softirq? Are there other values for
> irq_config? In which case there should be enums or something?
> I can't find the patch that describes this.

0 means as-is, 1 means threaded / sleeping locks are okay.

> > --- a/kernel/time/tick-sched.c
> > +++ b/kernel/time/tick-sched.c
> > @@ -245,6 +245,7 @@ static void nohz_full_kick_func(struct irq_work *work)
> >  
> >  static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
> >  	.func = nohz_full_kick_func,
> > +	.flags = ATOMIC_INIT(IRQ_WORK_HARD_IRQ),
> >  };
> 
> I get why these need to be in hardirq but some basic explanations for
> ordinary mortals as to why those two specifically and not all the others
> (and there are many) would have been nice.

Is the documentation patch in this series any good?

> Thanks.

Sebastian