linux-kernel - RE: [V5 PATCH 2/4] panic/x86: Allow cpus to save registers even if they are looping in NMI context

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Message-ID: <04EAB7311EE43145B2D3536183D1A84454A2A444@GSjpTKYDCembx31.service.hitachi.net>
Date:	Wed, 25 Nov 2015 05:57:34 +0000
From:	河合英宏 / KAWAI，HIDEHIRO 
	<hidehiro.kawai.ez@...achi.com>
To:	"'Steven Rostedt'" <rostedt@...dmis.org>,
	Borislav Petkov <bp@...en8.de>
CC:	Jonathan Corbet <corbet@....net>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vivek Goyal <vgoyal@...hat.com>, Baoquan He <bhe@...hat.com>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	平松雅巳 / HIRAMATU，MASAMI 
	<masami.hiramatsu.pt@...achi.com>
Subject: RE: [V5 PATCH 2/4] panic/x86: Allow cpus to save registers even if
 they are looping in NMI context

> On Tue, Nov 24, 2015 at 11:48:53AM +0100, Borislav Petkov wrote:
> >
> > > +	 */
> > > +	while (!raw_spin_trylock(&nmi_reason_lock))
> > > +		poll_crash_ipi_and_callback(regs);
> >
> > Waaait a minute: so if we're getting NMIs broadcasted on every core but
> > we're *not* crash dumping, we will run into here too. This can't be
> > right. :-\
> 
> This only does something if crash_ipi_done is set, which means you are killing
> the box. But perhaps a comment that states that here would be useful, or maybe
> just put in the check here. 

OK, I'll add more comments around this.

> There's no need to make it depend on SMP, as
> raw_spin_trylock() will turn to just ({1}) for UP, and that code wont even be
> hit.

I'll integrate these SMP and UP versions with a comment about
that.

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