linux-kernel - Re: [v2 PATCH 1/3] panic: Change nmi

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Date:	Wed, 2 Mar 2016 09:03:06 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Michal Hocko <mhocko@...nel.org>,
	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Mingarelli <thomas.mingarelli@....com>,
	Wim Van Sebroeck <wim@...ana.be>,
	Corey Minyard <minyard@....org>,
	Javi Merino <javi.merino@....com>,
	linux-watchdog@...r.kernel.org,
	"Steven Rostedt (Red Hat)" <rostedt@...dmis.org>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	linux-kernel@...r.kernel.org,
	Michal Nazarewicz <mina86@...a86.com>,
	Vitaly Kuznetsov <vkuznets@...hat.com>,
	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>,
	Borislav Petkov <bp@...en8.de>,
	Gobinda Charan Maji <gobinda.cemk07@...il.com>,
	Tejun Heo <tj@...nel.org>,
	Nicolas Iooss <nicolas.iooss_linux@....org>,
	openipmi-developer@...ts.sourceforge.net,
	Borislav Petkov <bp@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [v2 PATCH 1/3] panic: Change nmi_panic from macro to function

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
>>
>>
>