Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753987AbdLNSTp (ORCPT ); Thu, 14 Dec 2017 13:19:45 -0500 Received: from mail.kernel.org ([198.145.29.99]:51718 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753389AbdLNSTo (ORCPT ); Thu, 14 Dec 2017 13:19:44 -0500 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F28D821879 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=rostedt@goodmis.org Date: Thu, 14 Dec 2017 13:19:41 -0500 From: Steven Rostedt To: Peter Zijlstra Cc: LKML , Ingo Molnar , Thomas Gleixner , Andrew Morton Subject: Re: [PATCH] lockdep: Show up to three levels for a deadlock scenario Message-ID: <20171214131941.1f87f8ee@gandalf.local.home> In-Reply-To: <20171214175931.mlvr7lk7bcnsqu5i@hirez.programming.kicks-ass.net> References: <20171214123852.515257aa@gandalf.local.home> <20171214175931.mlvr7lk7bcnsqu5i@hirez.programming.kicks-ass.net> X-Mailer: Claws Mail 3.14.0 (GTK+ 2.24.31; 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 Content-Length: 1258 Lines: 25 On Thu, 14 Dec 2017 18:59:31 +0100 Peter Zijlstra wrote: > On Thu, Dec 14, 2017 at 12:38:52PM -0500, Steven Rostedt wrote: > > > > Currently, when lockdep detects a possible deadlock scenario that involves 3 > > or more levels, it just shows the chain, and a CPU sequence order of the > > first and last part of the scenario, leaving out the middle level and this > > can take a bit of effort to understand. By adding a third level, it becomes > > easier to see where the deadlock is. > > So is anybody actually using this? This (together with the callchain for > #0) is always the first thing of the lockdep output I throw away. Um, most people that post lockdep issues do (including myself). You are unique and understand lockdep inside and out, so this doesn't help you. I've had talks accepted on how to read lockdep output (having a talk on how to read output shows it's not trivial at all to do so). Most people have no idea what the lockdep output means. This is the only part that "normal" people appear to understand from it. I've seen this part of the output posted many times on the mailing list to discuss deadlocks. I've been asked by many people to add this change, I just never had time to implement it. -- Steve