linux-kernel - Re: [PATCH 1/3] panic: Disable crash_kexec_post

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Message-ID: <20150714142004.GB10792@redhat.com>
Date:	Tue, 14 Jul 2015 10:20:04 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	dwalker@...o99.com
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mips@...ux-mips.org, Baoquan He <bhe@...hat.com>,
	linux-sh@...r.kernel.org, linux-s390@...r.kernel.org,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>,
	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linuxppc-dev@...ts.ozlabs.org, linux-metag@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/3] panic: Disable crash_kexec_post_notifiers if kdump
 is not available

On Tue, Jul 14, 2015 at 01:59:19PM +0000, dwalker@...o99.com wrote:
> On Mon, Jul 13, 2015 at 08:19:45PM -0500, Eric W. Biederman wrote:
> > dwalker@...o99.com writes:
> > 
> > > On Fri, Jul 10, 2015 at 08:41:28AM -0500, Eric W. Biederman wrote:
> > >> Hidehiro Kawai <hidehiro.kawai.ez@...achi.com> writes:
> > >> 
> > >> > You can call panic notifiers and kmsg dumpers before kdump by
> > >> > specifying "crash_kexec_post_notifiers" as a boot parameter.
> > >> > However, it doesn't make sense if kdump is not available.  In that
> > >> > case, disable "crash_kexec_post_notifiers" boot parameter so that
> > >> > you can't change the value of the parameter.
> > >> 
> > >> Nacked-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> > >
> > > I think it would make sense if he just replaced "kdump" with "kexec".
> > 
> > It would be less insane, however it still makes no sense as without
> > kexec on panic support crash_kexec is a noop.  So the value of the
> > seeting makes no difference.
> 
> Can you explain more, I don't really understand what you mean. Are you suggesting
> the whole "crash_kexec_post_notifiers" feature has no value ?

If CONFIG_KEXEC=n, then crash_kexec() is a nop. So it does not matter
whether crash_kexec() is called before panic notifiers or after.

IOW, what do you gain by disabling crash_kexec_post_notifiers, in 
case of CONFIG_KEXEC=n?

Thanks
Vivek
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