Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754751AbZGUG4c (ORCPT ); Tue, 21 Jul 2009 02:56:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754541AbZGUG4a (ORCPT ); Tue, 21 Jul 2009 02:56:30 -0400 Received: from out02.mta.xmission.com ([166.70.13.232]:59502 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754424AbZGUG43 (ORCPT ); Tue, 21 Jul 2009 02:56:29 -0400 To: Lai Jiangshan Cc: Andrew Morton , Neil Horman , Vivek Goyal , Brayan Arraes , LKML References: <4A64672E.8020005@cn.fujitsu.com> <4A65598D.7020808@cn.fujitsu.com> From: ebiederm@xmission.com (Eric W. Biederman) Date: Mon, 20 Jul 2009 23:56:22 -0700 In-Reply-To: <4A65598D.7020808@cn.fujitsu.com> (Lai Jiangshan's message of "Tue\, 21 Jul 2009 14\:00\:45 +0800") Message-ID: User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-XM-SPF: eid=;;;mid=;;;hst=in02.mta.xmission.com;;;ip=76.21.114.89;;;frm=ebiederm@xmission.com;;;spf=neutral X-SA-Exim-Connect-IP: 76.21.114.89 X-SA-Exim-Rcpt-To: laijs@cn.fujitsu.com, linux-kernel@vger.kernel.org, brayan@yack.com.br, vgoyal@redhat.com, nhorman@tuxdriver.com, akpm@linux-foundation.org X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-DCC: XMission; sa04 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;Lai Jiangshan X-Spam-Relay-Country: X-Spam-Report: * -1.8 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.0 T_TM2_M_HEADER_IN_MSG BODY: T_TM2_M_HEADER_IN_MSG * -2.6 BAYES_00 BODY: Bayesian spam probability is 0 to 1% * [score: 0.0000] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa04 1397; Body=1 Fuz1=1 Fuz2=1] * 0.0 T_TooManySym_01 4+ unique symbols in subject * 0.0 XM_SPF_Neutral SPF-Neutral * 0.4 UNTRUSTED_Relay Comes from a non-trusted relay Subject: Re: [PATCH] sysrq, kdump: fix regression, revert "simplify sysrq-c handler" X-SA-Exim-Version: 4.2.1 (built Thu, 25 Oct 2007 00:26:12 +0000) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1559 Lines: 47 Lai Jiangshan writes: > Eric W. Biederman wrote: >> Lai Jiangshan writes: >> >>> 1) This fix breaks our tools. >>> This fix changes the ABI. panic_on_oops is default 0, >>> and a lots system do not specify the boot option "panic", >>> thus, Sysrq-c will not cause CrashDump(Kdump) as expected. >> >> How does it break your tools? > > Sysrq-c is known for causing a CrashDump. > This fix make Sysrq-c just causing an oops. > An oops in process context just kills current task and > does nothing. (panic_on_oops=0) > > Why we let a cleanup patch changes the kernel behavior so much? Because it seemed reasonable to be able to test the oops path as well. >>> 2) When CONFIG_KEXEC=n, Sysrq-c should become an invalid >>> command like Sysrq-D(CONFIG_LOCKDEP, show-all-locks). >>> But this fix makes it a valid command and let it do a >>> hazard thing: cause a page fault(NULL dereference) in kernel. >>> >>> So, we revert this fix. >> >> The idea was to extend sysrq-d to also be a way of testing NULL >> pointer dereferences. How is that a bad idea? >> > > When CONFIG_KEXEC=n, Crashdump is not available, > Sysrq-c should become an invalid command. Why should sysrq-c become an invalid command? What problem does this cause for you? Eric -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/