linux-kernel - Re: [RFC][PATCH -mmotm 1/4] Add static function calls of pstore to kexec path

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Date:	Tue, 19 Jul 2011 19:52:13 +0100
From:	Matthew Garrett <mjg@...hat.com>
To:	Seiji Aguchi <seiji.aguchi@....com>
Cc:	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Americo Wang <xiyou.wangcong@...il.com>,
	"tony.luck@...el.com" <tony.luck@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jarod Wilson <jwilson@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"dzickus@...hat.com" <dzickus@...hat.com>,
	"dle-develop@...ts.sourceforge.net" 
	<dle-develop@...ts.sourceforge.net>,
	Satoru Moriya <satoru.moriya@....com>
Subject: Re: [RFC][PATCH -mmotm 1/4] Add static function calls of pstore to
 kexec path

On Tue, Jul 19, 2011 at 02:48:22PM -0400, Seiji Aguchi wrote:
> >How is this safe? What happens if there's a pstore access in process
> >when you hit this codepath?
> 
> This will never happen because pstore_kmsg_dump_in_interrupt() is called after machine_crash_shutdown().
> 
> Panicked cpu sends NMI to all other cpus in machine_crash_shutdown() and they stop.

And how does that handle the case where we're halfway through a pstore
access when the NMI arrives? ERST, at least, has a complex state 
machine. You can't guarantee what starting one transaction without 
completing one that was in process will do.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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