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Subject: Re: [RFC 6/6] x86, NMI, Remove do_nmi_callback logic
From: Huang Ying <ying.huang@intel.com>
To: Don Zickus <dzickus@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>, "H. Peter Anvin" <hpa@zytor.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Andi Kleen <andi@firstfloor.org>
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Date: Mon, 13 Sep 2010 10:27:16 +0800
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On Sat, 2010-09-11 at 00:13 +0800, Don Zickus wrote:
> On Fri, Sep 10, 2010 at 10:51:05AM +0800, Huang Ying wrote:
> >  
> > +#if defined(CONFIG_X86_LOCAL_APIC) && !defined(CONFIG_LOCKUP_DETECTOR)
> > +extern int nmi_watchdog_tick(struct pt_regs *regs);
> > +#else
> > +static inline int nmi_watchdog_tick(struct pt_regs *regs)
> > +{
> > +	return 0;
> > +}
> > +#endif
> > +
> >  extern atomic_t nmi_active;
> >  extern unsigned int nmi_watchdog;
> >  #define NMI_NONE	0
> 
> <snip>
> 
> > @@ -421,12 +429,8 @@ static notrace __kprobes void default_do
> >  	}
> >  	raw_spin_unlock(&nmi_reason_lock);
> >  
> > -#if defined(CONFIG_X86_LOCAL_APIC) && !defined(CONFIG_LOCKUP_DETECTOR)
> > -	if (nmi_watchdog_tick(regs, reason))
> > -		return;
> > -	if (do_nmi_callback(regs, smp_processor_id()))
> > +	if (nmi_watchdog_tick(regs))
> >  		return;
> > -#endif
> >  
> >  	if (notify_die(DIE_NMIUNKNOWN, "nmi_unknown", regs, reason, 2, SIGINT)
> >  	    == NOTIFY_STOP)
> 
> I wonder if these two chunks are going to confuse people when they read
> the code.  The old nmi watchdog exists in the arch/x86 area but the new
> nmi watchdog code is now in kernel/watchdog.c.
> 
> If someone sees nmi_watchdog_tick() here will they assume the nmi watchdog
> code is still inside arch/x86?
> 
> I would suggest keep it wrapped with CONFIG_LOCKUP_DETECTOR to make it
> obvious.  Thoughts?

Is it planned to remove old NMI watchdog implementation in near future?

If it is not, I think it is better to document/comment the two
implementation more explicitly, maybe in nmi_watchdog_tick() comments. I
suspect nmi_watchdog_tick() wrapped with "!
defined(CONFIG_LOCKUP_DETECTOR)" will make people more confused.

Best Regards,
Huang Ying