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

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Message-ID: <20110719194036.GA25558@srcf.ucam.org>
Date:	Tue, 19 Jul 2011 20:40:36 +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 08:27:54PM +0100, Matthew Garrett wrote:
> On Tue, Jul 19, 2011 at 03:14:22PM -0400, Seiji Aguchi wrote:
> > 
> > >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?
> 
> If there's already locking involved, what benefit does removing the lock 
> in the pstore code give? You'll just hang when you hit the erst code 
> instead of the pstore code.

I'm sorry, you're right, this is a trylock so we won't hang in this 
case. We should probably document that in the pstore documentation to 
ensure that any future backends have the same behaviour.

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