From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752603AbZIICCk (ORCPT ); Tue, 8 Sep 2009 22:02:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751081AbZIICCj (ORCPT ); Tue, 8 Sep 2009 22:02:39 -0400 Received: from out02.mta.xmission.com ([166.70.13.232]:33690 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751043AbZIICCj (ORCPT ); Tue, 8 Sep 2009 22:02:39 -0400 To: rostedt@goodmis.org Cc: Li Zefan , Ingo Molnar , Frederic Weisbecker , LKML References: <4AA70198.9070500@cn.fujitsu.com> <4AA701B3.704@cn.fujitsu.com> <1252460366.11070.2.camel@gandalf.stny.rr.com> From: ebiederm@xmission.com (Eric W. Biederman) Date: Tue, 08 Sep 2009 19:02:37 -0700 In-Reply-To: <1252460366.11070.2.camel@gandalf.stny.rr.com> (Steven Rostedt's message of "Tue\, 08 Sep 2009 21\:39\:26 -0400") 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=in01.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: rostedt@goodmis.org, linux-kernel@vger.kernel.org, fweisbec@gmail.com, mingo@elte.hu, lizf@cn.fujitsu.com X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-DCC: XMission; sa01 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;rostedt@goodmis.org X-Spam-Relay-Country: X-Spam-Report: * -1.8 ALL_TRUSTED Passed through trusted hosts only via SMTP * 1.5 XMNoVowels Alpha-numberic number with no vowels * 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 * [sa01 1397; Body=1 Fuz1=1 Fuz2=1] * 0.0 XM_SPF_Neutral SPF-Neutral * 0.4 UNTRUSTED_Relay Comes from a non-trusted relay Subject: Re: [PATCH 2/2] tracing/events: Add kexec tracepoints X-SA-Exim-Version: 4.2.1 (built Thu, 25 Oct 2007 00:26:12 +0000) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Steven Rostedt writes: > On Tue, 2009-09-08 at 18:27 -0700, Eric W. Biederman wrote: >> Li Zefan writes: >> >> > When panic, save in ring buffer the time when crash happened, >> > the panic message, etc. And the data can be retrieved from >> > core dump file using flight-recorder, which is going to be a >> > module of the crash utility. >> > >> > Also if we implement flight-recorder in perf tool, those trace >> > outputs can be used by perf tool. >> >> Please let's keep dynamic code out of crash_kexec if we can. > > What dynamic code? It's a tracepoint not something like the function > tracer. It is activated via a bit test and a jmp. Not very dynamic. The philosophy of the crash dump code is that the kernel is broken trust as little as possible. Within a few seconds we should be able to get the time from the kernel that saves the crash dump so I don't see how adding a trace point adds anything into that code path except an unnecessary dependency that might have broken. Or in short you have a full user space to add features to. Please don't features to the critical kernel magic that gets you to userspace. Eric