On Tue 24-11-15 10:05:10, Steven Rostedt wrote:
> On Fri, Nov 20, 2015 at 06:36:44PM +0900, Hidehiro Kawai wrote:
> > diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> > index 350dfb0..480a4fd 100644
> > --- a/include/linux/kernel.h
> > +++ b/include/linux/kernel.h
> > @@ -445,6 +445,19 @@ extern int sysctl_panic_on_stackoverflow;
> >  
> >  extern bool crash_kexec_post_notifiers;
> >  
> > +extern atomic_t panic_cpu;
> > +
> > +/*
> > + * A variant of panic() called from NMI context.
> > + * If we've already panicked on this cpu, return from here.
> > + */
> > +#define nmi_panic(fmt, ...)                                                
> > \
> > +   do {                                                            \
> > +           int this_cpu = raw_smp_processor_id();                  \
> > +           if (atomic_cmpxchg(&panic_cpu, -1, this_cpu) != this_cpu) \
> > +                   panic(fmt, ##__VA_ARGS__);                      \
> 
> Hmm,
> 
> What happens if:
> 
>       CPU 0:                          CPU 1:
>       ------                          ------
>       nmi_panic();
> 
>                                       nmi_panic();
>                                       <external nmi>
>                                       nmi_panic();

I thought that nmi_panic is called only from the nmi context. If so how
can we get a nested NMI like that?
-- 
Michal Hocko
SUSE Labs
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