linux-kernel - Re: [PATCH 3/3] hpwdt: Use nmi_panic() when kernel panics in NMI handler

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Message-ID: <56D5049C.50207@roeck-us.net>
Date:	Mon, 29 Feb 2016 18:55:24 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Mingarelli <thomas.mingarelli@....com>,
	Wim Van Sebroeck <wim@...ana.be>,
	Corey Minyard <minyard@....org>
Cc:	linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org,
	Michal Hocko <mhocko@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	openipmi-developer@...ts.sourceforge.net
Subject: Re: [PATCH 3/3] hpwdt: Use nmi_panic() when kernel panics in NMI
 handler

On 02/29/2016 05:50 PM, Hidehiro Kawai wrote:
> commit 58c5661f2144 ("panic, x86: Allow CPUs to save registers even
> if looping in NMI context") introduced nmi_panic() which prevents
> concurrent/recursive execution of panic().  It also saves registers
> for the crash dump on x86.
>
> hpwdt driver can call panic() from NMI handler, so replace it with
> nmi_panic().
>
> Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>
> Cc: Thomas Mingarelli <thomas.mingarelli@....com>
> Cc: Wim Van Sebroeck <wim@...ana.be>
> Cc: Guenter Roeck <linux@...ck-us.net>
> Cc: linux-watchdog@...r.kernel.org
> ---
>   drivers/watchdog/hpwdt.c |   12 ++++++++++--
>   1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/watchdog/hpwdt.c b/drivers/watchdog/hpwdt.c
> index 92443c3..fd0486f 100644
> --- a/drivers/watchdog/hpwdt.c
> +++ b/drivers/watchdog/hpwdt.c
> @@ -496,11 +496,12 @@ static int hpwdt_pretimeout(unsigned int ulReason, struct pt_regs *regs)
>
>   	if (!is_icru && !is_uefi) {
>   		if (cmn_regs.u1.ral == 0) {
> -			panic("An NMI occurred, "
> +			nmi_panic(regs, "An NMI occurred, "
>   				"but unable to determine source.\n");

This message should really be in a single line.
Sure, strictly speaking that should be done in a separate patch,
but since you touch the line you might as well fix it.

> +			goto handled;

The goto is unnecessary. Just return NMI_HANDLED.

>   		}
>   	}
> -	panic("An NMI occurred. Depending on your system the reason "
> +	nmi_panic(regs, "An NMI occurred. Depending on your system the reason "
>   		"for the NMI is logged in any one of the following "
>   		"resources:\n"
>   		"1. Integrated Management Log (IML)\n"
> @@ -508,6 +509,13 @@ static int hpwdt_pretimeout(unsigned int ulReason, struct pt_regs *regs)
>   		"3. OA Forward Progress Log\n"
>   		"4. iLO Event Log");
>
> +handled:
> +	/*
> +	 * Returning from nmi_panic() means this CPU was processing panic()
> +	 * before NMI.  Return NMI_HANDLED and go back to panic routines.
> +	 */

I don't think this comment adds much if any value.

> +	return NMI_HANDLED;
> +
>   out:

Any goto to this label does no longer serve a useful purpose (if it ever served one),
and should be replaced with "return NMI_DONE;"

>   	return NMI_DONE;
>   }
>
>
>