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SubjectRe: [WARNING] kernel/rcu/tree.c:1058 rcu_irq_enter+0x15/0x20
On Wed, 30 Sep 2020 21:22:42 +0200
Peter Zijlstra <peterz@infradead.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@infradead.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

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