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

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Date:	Tue, 1 Mar 2016 03:54:37 +0000
From:	河合英宏 / KAWAI，HIDEHIRO 
	<hidehiro.kawai.ez@...achi.com>
To:	"'Guenter Roeck'" <linux@...ck-us.net>,
	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-watchdog@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	"openipmi-developer@...ts.sourceforge.net" 
	<openipmi-developer@...ts.sourceforge.net>
Subject: RE: [PATCH 3/3] hpwdt: Use nmi_panic() when kernel panics in NMI
 handler

Hi Guenter,

Thanks for the review.

> 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.

OK, I'll combine them.

> > +			goto handled;
> 
> The goto is unnecessary. Just return NMI_HANDLED.

Sure, I'll do that.

> 
> >   		}
> >   	}
> > -	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.

So, I remove this comment.  NMI_HANDLED would be self-explanatory.

> > +	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;"

I'll fix it.  It will become a bit simpler.

Thanks,

--
Hidehiro Kawai
Hitachi, Ltd. Research & Development Group