Return-Path: linux-nfs-owner@vger.kernel.org Received: from mx1.redhat.com ([209.132.183.28]:35682 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758009Ab3CFMGv (ORCPT ); Wed, 6 Mar 2013 07:06:51 -0500 Date: Wed, 6 Mar 2013 07:06:31 -0500 From: Jeff Layton To: Ingo Molnar Cc: Mandeep Singh Baines , Tejun Heo , "J. Bruce Fields" , "Myklebust, Trond" , Oleg Nesterov , Ming Lei , Linux Kernel Mailing List , "linux-nfs@vger.kernel.org" , "Rafael J. Wysocki" , Andrew Morton , Linus Torvalds , Peter Zijlstra , Thomas Gleixner Subject: Re: LOCKDEP: 3.9-rc1: mount.nfs/4272 still has locks held! Message-ID: <20130306070631.0f326014@tlielax.poochiereds.net> In-Reply-To: <20130306090914.GA6030@gmail.com> References: <20130304205307.GA13527@redhat.com> <4FA345DA4F4AE44899BD2B03EEEC2FA9286AEEB0@sacexcmbx05-prd.hq.netapp.com> <20130305082308.6607d4db@tlielax.poochiereds.net> <20130305174648.GF12795@htj.dyndns.org> <20130305174954.GG12795@htj.dyndns.org> <20130305231110.GK15816@fieldses.org> <20130306010507.GL15816@fieldses.org> <20130306011623.GG1227@htj.dyndns.org> <20130306090914.GA6030@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-nfs-owner@vger.kernel.org List-ID: On Wed, 6 Mar 2013 10:09:14 +0100 Ingo Molnar wrote: > > * Mandeep Singh Baines wrote: > > > On Tue, Mar 5, 2013 at 5:16 PM, Tejun Heo wrote: > > > On Tue, Mar 05, 2013 at 08:05:07PM -0500, J. Bruce Fields wrote: > > >> If it's really just a 2-line patch to try_to_freeze(), could it just be > > >> carried out-of-tree by people that are specifically working on tracking > > >> down these problems? > > >> > > >> But I don't have strong feelings about it--as long as it doesn't result > > >> in the same known issues getting reported again and again.... > > > > > > Agreed, I don't think a Kconfig option is justified for this. If this > > > is really important, annotate broken paths so that it doesn't trigger > > > spuriously; otherwise, please just remove it. > > > > > > > Fair enough. Let's revert then. I'll rework to use a lockdep annotation. > > > > Maybe, add a new lockdep API: > > > > lockdep_set_held_during_freeze(lock); > > > > Then when we do the check, ignore any locks that set this bit. > > > > Ingo, does this seem like a reasonable design to you? > > Am I reading the discussion correctly that the new warnings show REAL potential > deadlock scenarios, which can hit real users and can lock their box up in entirely > real usage scenarios? > > If yes then guys we _really_ don't want to use lockdep annotation to _HIDE_ bugs. > We typically use them to teach lockdep about things it does not know about. > > How about fixing the deadlocks instead? > I do see how the freezer might fail to suspend certain tasks, but I don't see the deadlock scenario here in the NFS/RPC case. Can someone outline a situation where this might end up deadlocking? If not, then I'd be inclined to say that while this may be a problem, the warning is excessive... -- Jeff Layton