Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752732AbbHaJ5S (ORCPT <rfc822;w@1wt.eu>);
	Mon, 31 Aug 2015 05:57:18 -0400
Received: from mail7.hitachi.co.jp ([133.145.228.42]:37846 "EHLO
	mail7.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1752221AbbHaJ5Q (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Mon, 31 Aug 2015 05:57:16 -0400
From: =?utf-8?B?5rKz5ZCI6Iux5a6PIC8gS0FXQUnvvIxISURFSElSTw==?= 
	<hidehiro.kawai.ez@hitachi.com>
To: "'Peter Zijlstra'" <peterz@infradead.org>
CC: Jonathan Corbet <corbet@lwn.net>, Ingo Molnar <mingo@kernel.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>, Vivek Goyal <vgoyal@redhat.com>,
        "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>,
        "kexec@lists.infradead.org" <kexec@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Michal Hocko <mhocko@kernel.org>,
        =?utf-8?B?5bmz5p2+6ZuF5bezIC8gSElSQU1BVFXvvIxNQVNBTUk=?= 
	<masami.hiramatsu.pt@hitachi.com>
Subject: RE: [V3 PATCH 3/4] kexec: Fix race between panic() and
 crash_kexec() called directly
Thread-Topic: [V3 PATCH 3/4] kexec: Fix race between panic() and
 crash_kexec() called directly
Thread-Index: AQHQ0AtjXekgeO133USkzCimPcfuqJ4VA1yAgAJdTKCABPPXAIABVqwggAhInsD//24xgIAApHOg
Date: Mon, 31 Aug 2015 09:57:11 +0000
Message-ID: <04EAB7311EE43145B2D3536183D1A84454958A58@GSjpTKYDCembx31.service.hitachi.net>
References: <20150806054543.25766.29590.stgit@softrs>
 <20150806054543.25766.5914.stgit@softrs>
 <20150820230845.GF3161@worktop.event.rightround.com>
 <04EAB7311EE43145B2D3536183D1A8445493C868@GSjpTKYDCembx31.service.hitachi.net>
 <20150825145258.GS16853@twins.programming.kicks-ass.net>
 <04EAB7311EE43145B2D3536183D1A84454951595@GSjpTKYDCembx31.service.hitachi.net>
 <04EAB7311EE43145B2D3536183D1A8445495793E@GSjpTKYDCembx31.service.hitachi.net>
 <20150831090733.GI19282@twins.programming.kicks-ass.net>
In-Reply-To: <20150831090733.GI19282@twins.programming.kicks-ass.net>
Accept-Language: ja-JP, en-US
Content-Language: ja-JP
X-MS-Has-Attach: 
X-MS-TNEF-Correlator: 
x-originating-ip: [10.198.220.54]
Content-Type: text/plain; charset="utf-8"
MIME-Version: 1.0
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Transfer-Encoding: 8bit
X-MIME-Autoconverted: from base64 to 8bit by mail.home.local id t7V9vN9T014994
Content-Length: 1297
Lines: 40

> From: Peter Zijlstra [mailto:peterz@infradead.org]
> On Mon, Aug 31, 2015 at 08:53:11AM +0000, 河合英宏 / KAWAI，HIDEHIRO wrote:
> > > I understand your question.  I don't intend to permit the recursive
> > > call of crash_kexec() as for 'old_cpu != this_cpu' check.  That is
> > > needed for the case of panic() --> crash_kexec().  Since panic_cpu has
> > > already been set to this_cpu in panic() (please see PATCH 1/4), no one
> > > can run crash_kexec() without 'old_cpu != this_cpu' check.
> > >
> > > If you don't like this check, I would also be able to handle this case
> > > like below:
> > >
> > > crash_kexec()
> > > {
> > > 	old_cpu = atomic_cmpxchg(&panic_cpu, -1, this_cpu);
> > > 	if (old_cpu != -1)
> > > 		return;
> > >
> > > 	__crash_kexec();
> > > }
> > >
> > > panic()
> > > {
> > > 	atomic_cmpxchg(&panic_cpu, -1, this_cpu);
> > > 	__crash_kexec();
> > > ...
> > >
> >
> > Is that OK?
> 
> I suppose so, but I think me getting confused means comments can be
> added/improved.

OK, I'll improve comments and description in the next version.

Thanks!

Hidehiro Kawai
Hitachi, Ltd. Research & Development Group

????{.n?+???????+%?????ݶ??w??{.n?+????{??G?????{ay?ʇڙ?,j??f???h?????????z_??(?階?ݢj"???m??????G????????????&???~???iO???z??v?^?m????????????I?