Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753017AbbHVCfa (ORCPT ); Fri, 21 Aug 2015 22:35:30 -0400 Received: from mail7.hitachi.co.jp ([133.145.228.42]:48884 "EHLO mail7.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752261AbbHVCf2 (ORCPT ); Fri, 21 Aug 2015 22:35:28 -0400 From: =?utf-8?B?5rKz5ZCI6Iux5a6PIC8gS0FXQUnvvIxISURFSElSTw==?= To: "'Peter Zijlstra'" CC: Jonathan Corbet , Ingo Molnar , "Eric W. Biederman" , "H. Peter Anvin" , Andrew Morton , Thomas Gleixner , Vivek Goyal , "linux-doc@vger.kernel.org" , "x86@kernel.org" , "kexec@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Michal Hocko , =?utf-8?B?5bmz5p2+6ZuF5bezIC8gSElSQU1BVFXvvIxNQVNBTUk=?= 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: AQHQ0AtjXekgeO133USkzCimPcfuqJ4VA1yAgAJdTKA= Date: Sat, 22 Aug 2015 02:35:24 +0000 Message-ID: <04EAB7311EE43145B2D3536183D1A8445493C868@GSjpTKYDCembx31.service.hitachi.net> References: <20150806054543.25766.29590.stgit@softrs> <20150806054543.25766.5914.stgit@softrs> <20150820230845.GF3161@worktop.event.rightround.com> In-Reply-To: <20150820230845.GF3161@worktop.event.rightround.com> Accept-Language: ja-JP, en-US Content-Language: ja-JP X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.198.220.34] Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from base64 to 8bit by mail.home.local id t7M2ZuKK003206 Content-Length: 1513 Lines: 47 > From: Peter Zijlstra [mailto:peterz@infradead.org] > > On Thu, Aug 06, 2015 at 02:45:43PM +0900, Hidehiro Kawai wrote: > > void crash_kexec(struct pt_regs *regs) > > { > > + int old_cpu, this_cpu; > > + > > + /* > > + * `old_cpu == -1' means we are the first comer and crash_kexec() > > + * was called without entering panic(). > > + * `old_cpu == this_cpu' means crash_kexec() was called from panic(). > > + */ > > + this_cpu = raw_smp_processor_id(); > > + old_cpu = atomic_cmpxchg(&panic_cpu, -1, this_cpu); > > + if (old_cpu != -1 && old_cpu != this_cpu) > > + return; > > This allows recursive calling of crash_kexec(), the Changelog did not > mention that. Is this really required? What part are you arguing? Recursive call of crash_kexec() doesn't happen. In the first place, one of the purpose of this patch is to prevent a recursive call of crash_kexec() in the following case as I stated in the description: CPU 0: oops_end() crash_kexec() mutex_trylock() // acquired io_check_error() panic() crash_kexec() mutex_trylock() // failed to acquire infinite loop Also, the logic doesn't change form V1 (although the implementation changed), so I didn't add changelogs any more. Regards, 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?