From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758092AbZDPRUi (ORCPT ); Thu, 16 Apr 2009 13:20:38 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754965AbZDPRU3 (ORCPT ); Thu, 16 Apr 2009 13:20:29 -0400 Received: from casper.infradead.org ([85.118.1.10]:47137 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754683AbZDPRU2 (ORCPT ); Thu, 16 Apr 2009 13:20:28 -0400 Subject: Re: [PATCH 2/2] tracing/events/lockdep: move tracepoints within recursive protection From: Peter Zijlstra To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton , Thomas Gleixner , Frederic Weisbecker In-Reply-To: References: <20090416161543.199331330@goodmis.org> <20090416161746.831882528@goodmis.org> <1239900469.23397.3128.camel@laptop> Content-Type: text/plain Date: Thu, 16 Apr 2009 19:20:07 +0200 Message-Id: <1239902407.23397.3197.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.26.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2009-04-16 at 13:03 -0400, Steven Rostedt wrote: > On Thu, 16 Apr 2009, Peter Zijlstra wrote: > > > On Thu, 2009-04-16 at 12:15 -0400, Steven Rostedt wrote: > > > plain text document attachment > > > (0002-tracing-events-lockdep-move-tracepoints-within-recu.patch) > > > From: Steven Rostedt > > > > > > With the current location of the tracepoints in lockdep, the system > > > can hard lockup in minutes when the tracepoints are enabled. > > > > > > Moving the tracepoints outside inside the lockdep protection solves > > > the issue. > > > > NAK > > > > the idea is to eventually move lockdep on top of the tracepoints. The > > tracer should grow to be more robust and handle recursion itself. > > > > Its likely a case of the tracer using a spinlock or mutex in the > > tracepoint code. When I did the tracepoints I converted one such to a > > raw_spinlock_t in the trace_print code. > > Note, that the ring buffer and events are made to be recursive. That is, > it allows one event to trace within another event. But surely not in the same context. You could do a 4 level recursion protection like I did in perf-counter, not allowing recursion in: nmi, irq, softirq, process - context. That allows you to trace an irq while you're tracing something in process context, etc.. But not allow recursion on the same level. > If the tracepoint is > triggered by something within the trace point handler, then we are > screwed. That needs to be fixed. Exactly the thing you want to detect and warn about, preferably with a nice stack trace. > I have not seen what is triggering back into locking. The ring buffer and > what I can see by the event code, does not grab any locks besides raw > ones. Well, it used to all work, so something snuck in.