From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Date: Mon, 31 Aug 2015 11:07:33 +0200 From: Peter Zijlstra Subject: Re: [V3 PATCH 3/4] kexec: Fix race between panic() and crash_kexec() called directly Message-ID: <20150831090733.GI19282@twins.programming.kicks-ass.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> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <04EAB7311EE43145B2D3536183D1A8445495793E@GSjpTKYDCembx31.service.hitachi.net> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: =?utf-8?B?5rKz5ZCI6Iux5a6PIC8gS0FXQUnvvIxISURFSElSTw==?= Cc: "x86@kernel.org" , Jonathan Corbet , "linux-doc@vger.kernel.org" , "kexec@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Michal Hocko , Thomas Gleixner , "Eric W. Biederman" , "H. Peter Anvin" , =?utf-8?B?5bmz5p2+6ZuF5bezIC8gSElSQU1BVFXvvIxNQVNBTUk=?= , Andrew Morton , Ingo Molnar , Vivek Goyal T24gTW9uLCBBdWcgMzEsIDIwMTUgYXQgMDg6NTM6MTFBTSArMDAwMCwg5rKz5ZCI6Iux5a6PIC8g S0FXQUnvvIxISURFSElSTyB3cm90ZToKPiA+IEkgdW5kZXJzdGFuZCB5b3VyIHF1ZXN0aW9uLiAg SSBkb24ndCBpbnRlbmQgdG8gcGVybWl0IHRoZSByZWN1cnNpdmUKPiA+IGNhbGwgb2YgY3Jhc2hf a2V4ZWMoKSBhcyBmb3IgJ29sZF9jcHUgIT0gdGhpc19jcHUnIGNoZWNrLiAgVGhhdCBpcwo+ID4g bmVlZGVkIGZvciB0aGUgY2FzZSBvZiBwYW5pYygpIC0tPiBjcmFzaF9rZXhlYygpLiAgU2luY2Ug cGFuaWNfY3B1IGhhcwo+ID4gYWxyZWFkeSBiZWVuIHNldCB0byB0aGlzX2NwdSBpbiBwYW5pYygp IChwbGVhc2Ugc2VlIFBBVENIIDEvNCksIG5vIG9uZQo+ID4gY2FuIHJ1biBjcmFzaF9rZXhlYygp IHdpdGhvdXQgJ29sZF9jcHUgIT0gdGhpc19jcHUnIGNoZWNrLgo+ID4gCj4gPiBJZiB5b3UgZG9u J3QgbGlrZSB0aGlzIGNoZWNrLCBJIHdvdWxkIGFsc28gYmUgYWJsZSB0byBoYW5kbGUgdGhpcyBj YXNlCj4gPiBsaWtlIGJlbG93Ogo+ID4gCj4gPiBjcmFzaF9rZXhlYygpCj4gPiB7Cj4gPiAJb2xk X2NwdSA9IGF0b21pY19jbXB4Y2hnKCZwYW5pY19jcHUsIC0xLCB0aGlzX2NwdSk7Cj4gPiAJaWYg KG9sZF9jcHUgIT0gLTEpCj4gPiAJCXJldHVybjsKPiA+IAo+ID4gCV9fY3Jhc2hfa2V4ZWMoKTsK PiA+IH0KPiA+IAo+ID4gcGFuaWMoKQo+ID4gewo+ID4gCWF0b21pY19jbXB4Y2hnKCZwYW5pY19j cHUsIC0xLCB0aGlzX2NwdSk7Cj4gPiAJX19jcmFzaF9rZXhlYygpOwo+ID4gLi4uCj4gPiAKPiAK PiBJcyB0aGF0IE9LPwoKSSBzdXBwb3NlIHNvLCBidXQgSSB0aGluayBtZSBnZXR0aW5nIGNvbmZ1 c2VkIG1lYW5zIGNvbW1lbnRzIGNhbiBiZQphZGRlZC9pbXByb3ZlZC4KCl9fX19fX19fX19fX19f X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fCmtleGVjIG1haWxpbmcgbGlzdAprZXhl Y0BsaXN0cy5pbmZyYWRlYWQub3JnCmh0dHA6Ly9saXN0cy5pbmZyYWRlYWQub3JnL21haWxtYW4v bGlzdGluZm8va2V4ZWMK From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752601AbbHaJHp (ORCPT ); Mon, 31 Aug 2015 05:07:45 -0400 Received: from casper.infradead.org ([85.118.1.10]:40053 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751322AbbHaJHn (ORCPT ); Mon, 31 Aug 2015 05:07:43 -0400 Date: Mon, 31 Aug 2015 11:07:33 +0200 From: Peter Zijlstra To: =?utf-8?B?5rKz5ZCI6Iux5a6PIC8gS0FXQUnvvIxISURFSElSTw==?= 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 Message-ID: <20150831090733.GI19282@twins.programming.kicks-ass.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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <04EAB7311EE43145B2D3536183D1A8445495793E@GSjpTKYDCembx31.service.hitachi.net> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.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.