From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755006AbZFIPXU (ORCPT ); Tue, 9 Jun 2009 11:23:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753241AbZFIPXJ (ORCPT ); Tue, 9 Jun 2009 11:23:09 -0400 Received: from tomts5.bellnexxia.net ([209.226.175.25]:47362 "EHLO tomts5-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752171AbZFIPXH convert rfc822-to-8bit (ORCPT ); Tue, 9 Jun 2009 11:23:07 -0400 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AmAGAFgZLkpMQW1W/2dsb2JhbACBT4EwzVmECgU Date: Tue, 9 Jun 2009 11:23:02 -0400 From: Mathieu Desnoyers To: Dave Young Cc: Dave Jones , Pekka Enberg , "Rafael J. Wysocki" , Linux Kernel Mailing List , Kernel Testers List , cpufreq@vger.kernel.org, Rusty Russell , trenn@suse.de, sven.wegener@stealer.net, Venkatesh Pallipadi , mingo@elte.hu, Shaohua Li Subject: Re: [PATCH] remove rwsem lock from CPUFREQ_GOV_STOP call (second call site) Message-ID: <20090609152302.GA22784@Krystal> References: <84144f020906070621r1f480eaeief026d23662df380@mail.gmail.com> <1244447366.13471.4.camel@penberg-laptop> <20090608124844.GA17588@Krystal> <20090608143220.GC2516@redhat.com> <20090608152316.GA21033@Krystal> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8BIT In-Reply-To: X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.21.3-grsec (i686) X-Uptime: 11:22:25 up 101 days, 11:48, 4 users, load average: 0.85, 0.52, 0.47 User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Dave Young (hidave.darkstar@gmail.com) wrote: > On Mon, Jun 8, 2009 at 11:23 PM, Mathieu > Desnoyers wrote: > > * Dave Jones (davej@redhat.com) wrote: > >> On Mon, Jun 08, 2009 at 08:48:45AM -0400, Mathieu Desnoyers wrote: > >> > >>  > > > >> Bug-Entry       : http://bugzilla.kernel.org/show_bug.cgi?id=13475 > >>  > > > >> Subject         : suspend/hibernate lockdep warning > >>  > > > >> References      : http://marc.info/?l=linux-kernel&m=124393723321241&w=4 > >>  > > > > >>  > > > I suspect the following commit, after revert this patch I test 5 times > >>  > > > without lockdep warnings. > >>  > > > > >>  > > > commit b14893a62c73af0eca414cfed505b8c09efc613c > >>  > > > Author: Mathieu Desnoyers > >>  > > > Date:   Sun May 17 10:30:45 2009 -0400 > >>  > > > > >>  > > >        [CPUFREQ] fix timer teardown in ondemand governor > >>  > > > >>  > > The patch is probably not at fault here. I suspect it's some latent bug > >>  > > that simply got exposed by the change to cancel_delayed_work_sync(). In > >>  > > any case, Mathieu, can you take a look at this please? > >>  > > >>  > Yes, it's been looked at and discussed on the cpufreq ML. The short > >>  > answer is that they plan to re-engineer cpufreq and remove the policy > >>  > rwlock taken around almost every operations at the cpufreq level. > >>  > > >>  > The short-term solution, which is recognised as ugly, would be do to the > >>  > following before doing the cancel_delayed_work_sync() : > >>  > > >>  > unlock policy rwlock write lock > >>  > > >>  > lock policy rwlock write lock > >>  > > >>  > It basically works because this rwlock is unneeded for teardown, hence > >>  > the future re-work planned. > >>  > > >>  > I'm sorry I cannot prepare a patch current... I've got quite a few pages > >>  > of Ph.D. thesis due for the beginning of July. > >> > >> I'm kinda scared to touch this code at all for .30 due to the number of > >> unexpected gotchas we seem to run into every time we touch something > >> locking related.  So I'm inclined to just live with the lockdep warning > >> for .30, and see how the real fixes look for .31, and push them back > >> as -stable updates if they work out. > >> > >> > >> Venki, what are your thoughts? > >> > > > > Hi Dave, > > > > I've looked through the cpufreq code, and the following patch should > > address the call site I've missed in commit > > 42a06f2166f2f6f7bf04f32b4e823eacdceafdc9. I've followed all > > __cpufreq_set_policy call sites within cpufreq.c to make sure they all > > hold the rwsem write lock. An extra round of review would be good > > though. > > > > Can someone try the following patch and see if it fixes the regression ? > > Bad news, I have tried the patch and It does not fix the regression. > Can you provide the lockdep error message you get with the patch applied? Thanks, Mathieu > > My test machine is currently busy running long formal verifications, and > > therefore unavailable for kernel patch testing. It compiles fine on a > > 2.6.30-rc5 kernel with my (now mainlined) cpufreq patches applied. > > > > Mathieu > > > > > > remove rwsem lock from CPUFREQ_GOV_STOP call (second call site) > > > > commit  42a06f2166f2f6f7bf04f32b4e823eacdceafdc9 > > > > Missed a call site for CPUFREQ_GOV_STOP to remove the rwlock taken around the > > teardown. To make a long story short, the rwlock write-lock causes a circular > > dependency with cancel_delayed_work_sync(), because the timer handler takes the > > read lock. > > > > Note that all callers to __cpufreq_set_policy are taking the rwsem. All sysfs > > callers (writers) hold the write rwsem at the earliest sysfs calling stage. > > > > However, the rwlock write-lock is not needed upon governor stop. > > > > Signed-off-by: Mathieu Desnoyers > > CC: rjw@sisk.pl > > CC: mingo@elte.hu > > CC: Shaohua Li > > CC: Pekka Enberg > > CC: Dave Young > > CC: "Rafael J. Wysocki" > > CC: Rusty Russell > > CC: trenn@suse.de > > CC: sven.wegener@stealer.net > > CC: Venkatesh Pallipadi > > CC: cpufreq@vger.kernel.org > > --- > >  drivers/cpufreq/cpufreq.c |   11 ++++++++++- > >  1 file changed, 10 insertions(+), 1 deletion(-) > > > > Index: linux-2.6-lttng/drivers/cpufreq/cpufreq.c > > =================================================================== > > --- linux-2.6-lttng.orig/drivers/cpufreq/cpufreq.c      2009-06-08 10:20:48.000000000 -0400 > > +++ linux-2.6-lttng/drivers/cpufreq/cpufreq.c   2009-06-08 10:48:52.000000000 -0400 > > @@ -1697,8 +1697,17 @@ static int __cpufreq_set_policy(struct c > >                        dprintk("governor switch\n"); > > > >                        /* end old governor */ > > -                       if (data->governor) > > +                       if (data->governor) { > > +                               /* > > +                                * Need to release the rwsem around governor > > +                                * stop due to lock dependency between > > +                                * cancel_delayed_work_sync and the read lock > > +                                * taken in the delayed work handler. > > +                                */ > > +                               unlock_policy_rwsem_write(data->cpu); > >                                __cpufreq_governor(data, CPUFREQ_GOV_STOP); > > +                               lock_policy_rwsem_write(data->cpu); > > +                       } > > > >                        /* start new governor */ > >                        data->governor = policy->governor; > > > > > > -- > > Mathieu Desnoyers > > OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68 > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at  http://vger.kernel.org/majordomo-info.html > > Please read the FAQ at  http://www.tux.org/lkml/ > > > > > > -- > Regards > dave > -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68