Re: [Xen-devel] [PATCH v3 5/6] xen/rcu: add assertions to debug build

[Jürgen Groß <jgross@xxxxxxxx>]

On 04.03.20 14:42, Julien Grall wrote:
> Hi,
>
> On 04/03/2020 06:32, Juergen Gross wrote:
> > diff --git a/xen/include/xen/rcupdate.h b/xen/include/xen/rcupdate.h
> > index 31c8b86d13..9f6d420898 100644
> > --- a/xen/include/xen/rcupdate.h
> > +++ b/xen/include/xen/rcupdate.h
> > @@ -34,10 +34,40 @@
> >   #include <xen/cache.h>
> >   #include <xen/spinlock.h>
> >   #include <xen/cpumask.h>
> > -#include <xen/preempt.h>
> > +#include <xen/percpu.h>
> > +#include <asm/atomic.h>
> >   #define __rcu
> > +#ifndef NDEBUG
> > +DECLARE_PER_CPU(unsigned int, rcu_lock_cnt);
> > +
> > +static inline void rcu_quiesce_disable(void)
> > +{
> > +    this_cpu(rcu_lock_cnt)++;
> > +    arch_lock_acquire_barrier();
> I am not sure to understand the goal of this barrier. What are you 
> trying to protect against?
This is the result of a request by Roger, which seemed reasonable,
although I should have checked the suggested barrier type more
thoroughly.

He suggested to add barriers like in the former preempt_[en|dis]able()
cases, but to use the acquire and release barriers like in locks.

Thinking more about it I think a simple barrier() should do the trick as
only cpu local protection is needed.


Juergen

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