Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751276AbdH2AzX (ORCPT ); Mon, 28 Aug 2017 20:55:23 -0400 Received: from LGEAMRELO13.lge.com ([156.147.23.53]:45834 "EHLO lgeamrelo13.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751209AbdH2AzW (ORCPT ); Mon, 28 Aug 2017 20:55:22 -0400 X-Original-SENDERIP: 156.147.1.121 X-Original-MAILFROM: byungchul.park@lge.com X-Original-SENDERIP: 10.177.222.33 X-Original-MAILFROM: byungchul.park@lge.com Date: Tue, 29 Aug 2017 09:55:16 +0900 From: Byungchul Park To: Peter Zijlstra Cc: tj@kernel.org, johannes.berg@intel.com, mingo@kernel.org, tglx@linutronix.de, linux-kernel@vger.kernel.org, kernel-team@lge.com Subject: Re: [RFC] workqueue: remove manual lockdep uses to detect deadlocks Message-ID: <20170829005516.GB3240@X58A-UD3R> References: <1503650463-14582-1-git-send-email-byungchul.park@lge.com> <20170828065553.gikwc5zsuy2762eg@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170828065553.gikwc5zsuy2762eg@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1356 Lines: 31 On Mon, Aug 28, 2017 at 08:55:53AM +0200, Peter Zijlstra wrote: > On Fri, Aug 25, 2017 at 05:41:03PM +0900, Byungchul Park wrote: > > Hello all, > > > > This is _RFC_. > > > > I want to request for comments about if it's reasonable conceptually. If > > yes, I want to resend after working it more carefully. > > > > Could you let me know your opinions about this? > > > > ----->8----- > > From 448360c343477fff63df766544eec4620657a59e Mon Sep 17 00:00:00 2001 > > From: Byungchul Park > > Date: Fri, 25 Aug 2017 17:35:07 +0900 > > Subject: [RFC] workqueue: remove manual lockdep uses to detect deadlocks > > > > We introduced the following commit to detect deadlocks caused by > > wait_for_completion() in flush_{workqueue, work}() and other locks. But > > now LOCKDEP_COMPLETIONS is introduced, such works are automatically done > > by LOCKDEP_COMPLETIONS. So it doesn't have to be done manually anymore. > > Removed it. > > > > No.. the existing annotation is strictly better because it will _always_ > warn. It doesn't need to first observe things just right. In addition, the existing annotation is never good, but just able to detect deadlocks aggresively. However, it's inevitable to create false dependencies. I mean some dependencies between work/wq and any locks inside of each work might be false ones sometimes.