From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752535AbbALPh6 (ORCPT ); Mon, 12 Jan 2015 10:37:58 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:48288 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751905AbbALPh5 (ORCPT ); Mon, 12 Jan 2015 10:37:57 -0500 Date: Mon, 12 Jan 2015 16:37:47 +0100 From: Peter Zijlstra To: Sasha Levin Cc: linux-kernel@vger.kernel.org, mingo@redhat.com Subject: Re: [RFC 1/4] lockdep: additional lock specific information when dumping locks Message-ID: <20150112153747.GE25256@twins.programming.kicks-ass.net> References: <1421074631-18831-1-git-send-email-sasha.levin@oracle.com> <20150112150633.GD25256@twins.programming.kicks-ass.net> <54B3E466.2030006@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54B3E466.2030006@oracle.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 12, 2015 at 10:12:38AM -0500, Sasha Levin wrote: > The reason for my patch is simple: That might have maybe been good changelog material? > I'm fuzzing with hundreds of worker threads > which at some point trigger a complete system lockup for some reason. > > When lockdep dumps the list of held locks it shows that pretty much every one > of those threads is holding the lock which caused the lockup, which is incorrect > because it considers locks in the process of getting acquired as "held". > > This is my solution to that issue. I wanted to know which one of the threads is > really holding the lock rather than just waiting on it. > > Is there a better way to solve that problem? Sure, think moar, if the accompanying stack trace is in the middle of the blocking primitive, ignore the top held lock ;-) Alternatively, make better/more use of lock_acquired() and track the acquire vs acquired information in the held_lock (1 bit) and look at it when printing.