Subject: Re: [v2 PATCH 1/3] panic: Change nmi_panic from macro to function
To: Michal Hocko <mhocko@kernel.org>,
        Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
References: <20160302103624.5058.35844.stgit@softrs>
 <20160302103626.5058.74361.stgit@softrs>
 <20160302131824.GH26686@dhcp22.suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Thomas Mingarelli <thomas.mingarelli@hpe.com>,
        Wim Van Sebroeck <wim@iguana.be>, Corey Minyard <minyard@acm.org>,
        Javi Merino <javi.merino@arm.com>, linux-watchdog@vger.kernel.org,
        "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        linux-kernel@vger.kernel.org, Michal Nazarewicz <mina86@mina86.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>,
        Borislav Petkov <bp@alien8.de>,
        Gobinda Charan Maji <gobinda.cemk07@gmail.com>,
        Tejun Heo <tj@kernel.org>, Nicolas Iooss <nicolas.iooss_linux@m4x.org>,
        openipmi-developer@lists.sourceforge.net, Borislav Petkov <bp@suse.de>,
        Thomas Gleixner <tglx@linutronix.de>
From: Guenter Roeck <linux@roeck-us.net>
Message-ID: <56D71CCA.20809@roeck-us.net>
Date: Wed, 2 Mar 2016 09:03:06 -0800
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101
 Thunderbird/38.5.1
MIME-Version: 1.0
In-Reply-To: <20160302131824.GH26686@dhcp22.suse.cz>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
X-Authenticated_sender: linux@roeck-us.net
X-OutGoing-Spam-Status: No, score=0.0
X-AntiAbuse: This header was added to track abuse, please include it with any abuse report
X-AntiAbuse: Primary Hostname - bh-25.webhostbox.net
X-AntiAbuse: Original Domain - vger.kernel.org
X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12]
X-AntiAbuse: Sender Address Domain - roeck-us.net
X-Get-Message-Sender-Via: bh-25.webhostbox.net: authenticated_id: linux@roeck-us.net
X-Authenticated-Sender: bh-25.webhostbox.net: linux@roeck-us.net
X-Source: 
X-Source-Args: 
X-Source-Dir: 
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 1187
Lines: 44

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
>>
>>
>