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

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Message-ID: <5C4C569E8A4B9B42A84A977CF070A35B2C199C64E5@USINDEVS01.corp.hds.com>
Date:	Tue, 19 Jul 2011 15:14:22 -0400
From:	Seiji Aguchi <seiji.aguchi@....com>
To:	Matthew Garrett <mjg@...hat.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


>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.

As for ERST, write access is protected by raw_spin_trylock_irqsave(&erst_lock).
Are there anything I'm missing?

Seiji


>-----Original Message-----
>From: Matthew Garrett [mailto:mjg@...hat.com]
>Sent: Tuesday, July 19, 2011 2:52 PM
>To: Seiji Aguchi
>Cc: kexec@...ts.infradead.org; linux-kernel@...r.kernel.org; linux-mtd@...ts.infradead.org; Eric W. Biederman; Vivek
>Goyal; KOSAKI Motohiro; Americo Wang; tony.luck@...el.com; Andrew Morton; Jarod Wilson; hpa@...or.com; dzickus@...hat.com;
>dle-develop@...ts.sourceforge.net; Satoru Moriya
>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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