linux-kernel - Re: [WARNING] kernel/rcu/tree.c:1058 rcu_irq

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Message-ID: <20200930155222.6754ce6c@gandalf.local.home>
Date:   Wed, 30 Sep 2020 15:52:22 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [WARNING] kernel/rcu/tree.c:1058 rcu_irq_enter+0x15/0x20

On Wed, 30 Sep 2020 21:22:42 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Wed, Sep 30, 2020 at 03:10:26PM -0400, Steven Rostedt wrote:
> > On Wed, 30 Sep 2020 20:13:23 +0200
> > Peter Zijlstra <peterz@...radead.org> wrote:
> >   
> > >  diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h  
> > > > index 6a584b3e5c74..3e5bc1dd71c6 100644
> > > > --- a/include/linux/lockdep.h
> > > > +++ b/include/linux/lockdep.h
> > > > @@ -550,7 +550,8 @@ do {									\
> > > >  
> > > >  #define lockdep_assert_irqs_disabled()					\
> > > >  do {									\
> > > > -	WARN_ON_ONCE(debug_locks && raw_cpu_read(hardirqs_enabled));	\
> > > > +	WARN_ON_ONCE(debug_locks && raw_cpu_read(hardirqs_enabled) &&	\
> > > > +           likely(!(current->lockdep_recursion & LOCKDEP_RECURSION_MASK)));\
> > > >  } while (0)    
> > > 
> > > Blergh, IIRC there's header hell that way. The sane fix is killing off
> > > that trace_*_rcuidle() disease.  
> > 
> > Really?
> > 
> > I could run this through all my other tests to see if that is the case.
> > That is, to see if it stumbles across header hell.  
> 
> I went through a lot of pain to make that per-cpu to avoid using
> current. But that might've been driven by
> lockdep_assert_preemption_disabled(), which is used in seqlock.h which
> in turn is included all over the place.
> 
> That said, there's at least two things we can do:
> 
>  - make lockdep_recursion per-cpu too, IIRC we only ever set that when
>    we have IRQs disabled anyway.
> 
> OR
> 
>  - inspired by the above, as can save/clear - restore hardirqs_enabled
>    when we frob lockdep_recursion.
> 
> Admittedly, the second is somewhat gross :-)

I think making lockdep_recursion percpu sounds like the best approach.

-- Steve