Re: [v2 PATCH 1/3] panic: Change nmi_panic from macro to function

[Guenter Roeck]

On 03/02/2016 05:18 AM, Michal Hocko wrote:
> On Wed 02-03-16 19:36:26, Hidehiro Kawai wrote:
> [...]
> > +void nmi_panic(struct pt_regs *regs, const char *fmt, ...)
>
> Do we really need vargs? All the current users seem to be OK with a
> simple string. This makes the code slightly more complicated without any
> apparent reason.
>
> > +{
> > +	static char buf[1024]; /* protected by panic_cpu */

I am also not too happy with this additional stack allocation.
panic() itself takes varargs. Can those be passed on ?
I understand this would need something like vpanic(), so
maybe that isn't feasible.

Dropping the format, at least for now, might be a simpler option.

Guenter

> > +	va_list args;
> > +	int old_cpu, cpu;
> > +
> > +	cpu = raw_smp_processor_id();
> > +	old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, cpu);
> > +
> > +	if (old_cpu == PANIC_CPU_INVALID) {
> > +		va_start(args, fmt);
> > +		vsnprintf(buf, sizeof(buf), fmt, args);
> > +		va_end(args);
> > +
> > +		panic("%s", buf);
> > +	} else if (old_cpu != cpu)
> > +		nmi_panic_self_stop(regs);
> > +}
> > +EXPORT_SYMBOL(nmi_panic);
> > +
> >   /**
> >    *	panic - halt the system
> >    *	@fmt: The text string to print