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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Date:	Tue, 24 Nov 2015 14:37:00 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Borislav Petkov <bp@...en8.de>
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,
	Michal Hocko <mhocko@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Masami Hiramatsu <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. 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.

-- Steve

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