linux-kernel - Re: [V5 PATCH 1/4] panic/x86: Fix re-entrance problem due to panic on NMI

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Date:	Tue, 24 Nov 2015 15:45:28 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>,
	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, x86@...nel.org,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Subject: Re: [V5 PATCH 1/4] panic/x86: Fix re-entrance problem due to panic
 on NMI

On Tue, 24 Nov 2015 21:27:13 +0100
Michal Hocko <mhocko@...nel.org> wrote:


> > What happens if:
> > 
> > 	CPU 0:				CPU 1:
> > 	------				------
> > 	nmi_panic();
> > 
> > 					nmi_panic();
> > 					<external nmi>
> > 					nmi_panic();  
> 
> I thought that nmi_panic is called only from the nmi context. If so how
> can we get a nested NMI like that?

Nevermind. I was thinking the external NMI could nest, but I'm guessing
it cant. Anyway, the patches later on modify this code which checks for
something other than != this_cpu, which makes this issue mute even if
it could nest.

-- Steve
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