linux-kernel - Re: [RFC 6/6] x86, NMI, Remove do_nmi

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Date:	Mon, 13 Sep 2010 08:24:27 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Huang Ying <ying.huang@...el.com>
Cc:	Don Zickus <dzickus@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [RFC 6/6] x86, NMI, Remove do_nmi_callback logic


* Huang Ying <ying.huang@...el.com> wrote:

> 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?

Yes. With the new Pentium4 PMU driver we've covered the last 
old-NMI-watchdog hardware support corner too, so we can and should 
remove the old code. (keeping the boot option to stay compatible)

Thanks,

	Ingo
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