Hi Steven,

> From: Steven Rostedt [mailto:rostedt@goodmis.org]
> On Tue, Nov 24, 2015 at 11:48:53AM +0100, Borislav Petkov wrote:
> > > +	 */
> > > +	while (!raw_spin_trylock(&nmi_reason_lock))
> > > +		poll_crash_ipi_and_callback(regs);
> >
> > Waaait a minute: so if we're getting NMIs broadcasted on every core but
> > we're *not* crash dumping, we will run into here too. This can't be
> > right. :-\
> 
> This only does something if crash_ipi_done is set, which means you are killing
> the box. But perhaps a comment that states that here would be useful, or maybe
> just put in the check here. There's no need to make it depend on SMP, as
> raw_spin_trylock() will turn to just ({1}) for UP, and that code wont even be
> hit.

It seems that poll_crash_ipi_and_callback (now renamed to run_crash_ipi_callback)
is referred for UP if CONFIG_DEBUG_SPINLOCK=y, and it causes a build error
as below.  run_crash_ipi_callback refers crash_ipi_issued and crash_nmi_callback,
which are defined only if CONFIG_SMP=y.  So we need to defined it separately
for SMP and UP.

I'll resend this patch later.

> Hi Hidehiro,
> 
> [auto build test ERROR on v4.4-rc4]
> [also build test ERROR on next-20151209]
> [cannot apply to tip/x86/core]
> 
> url:
> https://github.com/0day-ci/linux/commits/Hidehiro-Kawai/Fix-race-issues-among-panic-NMI-and-crash_kexec/20151210-095
> 254
> config: x86_64-randconfig-s4-12101030 (attached as .config)
> reproduce:
>         # save the attached .config to linux build tree
>         make ARCH=x86_64
> 
> All errors (new ones prefixed by >>):
> 
>    arch/x86/built-in.o: In function `do_nmi':
> >> (.text+0x7339): undefined reference to `run_crash_ipi_callback'
> 
> ---
> 0-DAY kernel test infrastructure                Open Source Technology Center
> https://lists.01.org/pipermail/kbuild-all                   Intel Corporation
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