From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755459AbcA1OTA (ORCPT ); Thu, 28 Jan 2016 09:19:00 -0500 Received: from smtprelay0062.hostedemail.com ([216.40.44.62]:45686 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752703AbcA1OS5 (ORCPT ); Thu, 28 Jan 2016 09:18:57 -0500 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,rostedt@goodmis.org,:::::::::::,RULES_HIT:41:355:379:541:599:800:960:973:988:989:1260:1277:1311:1313:1314:1345:1359:1437:1515:1516:1518:1534:1540:1593:1594:1711:1730:1747:1777:1792:2393:2553:2559:2562:2895:2901:3138:3139:3140:3141:3142:3352:3622:3865:3866:3867:3868:3870:3871:3872:3873:3874:4250:4470:5007:6261:7875:9707:10004:10400:10848:10967:11232:11658:11914:12296:12517:12519:12740:13069:13161:13200:13229:13311:13357:14096:14097:14659:21080:30054:30070:30090:30091,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:none,Custom_rules:0:0:0,LFtime:2,LUA_SUMMARY:none X-HE-Tag: glove70_6b15b0a24185a X-Filterd-Recvd-Size: 2010 Date: Thu, 28 Jan 2016 09:18:54 -0500 From: Steven Rostedt To: Peter Zijlstra Cc: Mathieu Desnoyers , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, "Paul E. McKenney" Subject: Re: [RFC][BUG] tracer: Fails to work Message-ID: <20160128091854.45d0ac2b@gandalf.local.home> In-Reply-To: <20160128135733.GQ6356@twins.programming.kicks-ass.net> References: <20160128080859.GB6357@twins.programming.kicks-ass.net> <1069612139.6639.1453988280286.JavaMail.zimbra@efficios.com> <20160128135733.GQ6356@twins.programming.kicks-ass.net> X-Mailer: Claws Mail 3.13.1 (GTK+ 2.24.29; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 28 Jan 2016 14:57:33 +0100 Peter Zijlstra wrote: > On Thu, Jan 28, 2016 at 01:38:00PM +0000, Mathieu Desnoyers wrote: > > > Thoughts ? > > So ideally dumping the trace data would not depend on any of that, > because I can break it all :-) > > Not being able to access the trace data completely and utterly defeats > the purpose of having a tracer in the first place. > The solution is to use trace_pipe. That's for live tracing (or in this case, tracing when the system gets corrupted). I may update the tracing documentation to note this. The trace file preserves the data it reads, and disables the ring buffer before reading it to keep the iterator from being corrupted. But that requires a somewhat working system (not a CPU being stuck). Hence, use trace_pipe for your debugging. The only thing you'll lose is the header that trace provides. -- Steve