From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755433AbdBGTrx (ORCPT ); Tue, 7 Feb 2017 14:47:53 -0500 Received: from mx1.redhat.com ([209.132.183.28]:47804 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752885AbdBGTqz (ORCPT ); Tue, 7 Feb 2017 14:46:55 -0500 Subject: Re: [PATCH v3 0/3] locking/spinlock_debug: Change it to a mostly fair lock To: Ingo Molnar , Peter Zijlstra References: <1486044929-7244-1-git-send-email-longman@redhat.com> <20170207084553.GW6500@twins.programming.kicks-ass.net> <20170207094816.GC9829@gmail.com> Cc: Ingo Molnar , linux-kernel@vger.kernel.org, Linus Torvalds , Thomas Gleixner , Peter Zijlstra , Andrew Morton , "Paul E. McKenney" From: Waiman Long Organization: Red Hat Message-ID: Date: Tue, 7 Feb 2017 14:46:31 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <20170207094816.GC9829@gmail.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Tue, 07 Feb 2017 19:46:35 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/07/2017 04:48 AM, Ingo Molnar wrote: > * Peter Zijlstra wrote: > >> On Thu, Feb 02, 2017 at 09:15:26AM -0500, Waiman Long wrote: >>> v2->v3: >>> - Keep the original v1 patches but move patch 3 of v2 in front so >>> as to disable GENERIC_LOCKBREAK when DEBUG_LOCK_ALLOC is on. >>> >>> v1->v2: >>> - Pack lockup and break_lock into a single 4-byte slot so as not >>> to in increase spinlock size when GENERIC_LOCKBREAK is >>> on. Hopefully that will be enough to fix a frame size too large >>> warning in 0-day build. >>> - Add a new patch to disable GENERIC_LOCKBREAK when DEBUG_LOCK_ALLOC >>> is on. >>> >>> The current debug spinlock implementation is a TATAS unfair lock. This >>> can occasionally lead to system lockup with a debug kernel because >>> of the unfairness of the lock rather than inherent locking problem. >>> >>> This patch set changes the debug spinlock implementation to a >>> mostly fair spinlock based on the MCS lock similar to what is done >>> in qspinlock. It also includes a patch that disable GENERIC_LOCKBREAK >>> when DEBUG_LOCK_ALLOC is on. >> >> An alternative is to just delete the thing entirely.. >> >> Ingo, much of what this thing does seems to be superseded by both >> lockdep and a reliable NMI watchdog. Is there still value in >> spinlock_debug? > So there's still early stages when the NMI watchdog is not running, and > spinlock-debug can detect lockups in raw locks that lockdep does not cover, right? > > But yeah ... it would simplify things all around, so I'm not unsympathetic to the > idea... > > I've Cc:-ed a few other locking gents. > > Thanks, > > Ingo I have no problem deleting the debug_spinlock code entirely. I can update the patch to delete the code if you guys think that is the right thing to do. Cheers, Longman