From: Viresh Kumar <viresh.kumar@linaro.org>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Shilpa Bhat <shilpabhatppc@gmail.com>,
Juri Lelli <juri.lelli@arm.com>,
Rafael Wysocki <rjw@rjwysocki.net>,
Lists linaro-kernel <linaro-kernel@lists.linaro.org>,
"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
Saravana Kannan <skannan@codeaurora.org>,
Peter Zijlstra <peterz@infradead.org>,
Michael Turquette <mturquette@baylibre.com>,
Steve Muckle <steve.muckle@linaro.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Morten Rasmussen <morten.rasmussen@arm.com>,
dietmar.eggemann@arm.com,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups
Date: Thu, 4 Feb 2016 11:21:08 +0530 [thread overview]
Message-ID: <20160204055108.GY3469@vireshk> (raw)
In-Reply-To: <CAJZ5v0hbhoS+1AaU12SFxz=r1-TOWq10yJ+ST7mVWcUubTbxFw@mail.gmail.com>
On 04-02-16, 00:50, Rafael J. Wysocki wrote:
> On Thu, Feb 4, 2016 at 12:31 AM, Shilpa Bhat <shilpabhatppc@gmail.com> wrote:
> > Sorry for the delayed report. But I see the below backtrace on Power8 box. It
> > has 4 chips with 128 cpus.
Honestly, I wasn't expecting you to test this stuff, but I really
appreciate you doing that.
Thanks a lot ..
> > [ 906.765768] Possible unsafe locking scenario:
> >
> > [ 906.765880] CPU0 CPU1
> > [ 906.765969] ---- ----
This race scenario is perhaps incomplete and difficult to understand
without below lines:
Governor's EXIT Update sampling rate from sysfs
lock(s_active#91);
> > [ 906.766058] lock(od_dbs_cdata.mutex);
> > [ 906.766170] lock(&dbs_data->mutex);
> > [ 906.766304] lock(od_dbs_cdata.mutex);
> > [ 906.766461] lock(s_active#91);
> > [ 906.766572]
> > *** DEADLOCK ***
>
> This is exactly right. We've avoided one deadlock only to trip into
> another one.
As we discussed on IRC, we haven't introduced this deadlock with the
current series. But this is what Juri has reported some days back,
while he tested linus/master on TC2.
> This happens because update_sampling_rate() acquires
> od_dbs_cdata.mutex which is held around cpufreq_governor_exit() by
> cpufreq_governor_dbs().
>
> Worse yet, a deadlock can still happen without (the new)
> dbs_data->mutex, just between s_active and od_dbs_cdata.mutex if
> update_sampling_rate() runs in parallel with
> cpufreq_governor_dbs()->cpufreq_governor_exit() and the latter wins
> the race.
>
> It looks like we need to drop the governor mutex before putting the
> kobject in cpufreq_governor_exit().
That wouldn't be trivial to implement as we discussed.
Okay, here is a proposal for the current series and the series's you
have post Rafael:
- Firstly, I would like to clarify that I don't have any issues with
rebasing on top of your series, it should be easy enough.
- One thing is for sure that nothing from these 3 series's is getting
merged in 4.5, as we aren't fixing the real issue Shilpa/Juril have
reported.
- I think the first 4 patches here are just fine and don't need any
updates. They actually do the right thing and makes code so much
cleaner.
- So, can we apply the first 4 patches (which you have already
applied to bleeding-edge) now and do all work on top of that ?
Again, I can rebase if you merge your patches first, no issues at all
:)
--
viresh
next prev parent reply other threads:[~2016-02-04 5:51 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-03 14:02 [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups Viresh Kumar
2016-02-03 14:02 ` [PATCH V2 1/7] cpufreq: governor: Treat min_sampling_rate as a governor-specific tunable Viresh Kumar
2016-02-05 2:31 ` Rafael J. Wysocki
2016-02-05 2:47 ` Viresh Kumar
2016-02-03 14:02 ` [PATCH V2 2/7] cpufreq: governor: New sysfs show/store callbacks for governor tunables Viresh Kumar
2016-02-03 16:17 ` Viresh Kumar
2016-02-03 14:02 ` [PATCH V2 3/7] cpufreq: governor: Drop unused macros for creating governor tunable attributes Viresh Kumar
2016-02-03 14:02 ` [PATCH V2 4/7] Revert "cpufreq: Drop rwsem lock around CPUFREQ_GOV_POLICY_EXIT" Viresh Kumar
2016-02-03 14:02 ` [PATCH V2 5/7] cpufreq: Merge cpufreq_offline_prepare/finish routines Viresh Kumar
2016-02-03 20:21 ` Saravana Kannan
2016-02-04 1:49 ` Viresh Kumar
2016-02-03 14:02 ` [PATCH V2 6/7] cpufreq: Call __cpufreq_governor() with policy->rwsem held Viresh Kumar
2016-02-03 14:02 ` [PATCH V2 7/7] cpufreq: Remove cpufreq_governor_lock Viresh Kumar
2016-02-04 6:43 ` Viresh Kumar
2016-02-03 15:54 ` [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups Juri Lelli
2016-02-03 16:10 ` Viresh Kumar
2016-02-03 17:20 ` Juri Lelli
2016-02-03 17:20 ` Rafael J. Wysocki
2016-02-03 23:31 ` Shilpa Bhat
2016-02-03 23:50 ` Rafael J. Wysocki
2016-02-04 5:51 ` Viresh Kumar [this message]
2016-02-04 11:09 ` Viresh Kumar
2016-02-04 17:43 ` Saravana Kannan
2016-02-04 17:44 ` Saravana Kannan
2016-02-04 18:18 ` Rafael J. Wysocki
2016-02-05 2:44 ` Viresh Kumar
2016-02-05 3:54 ` Rafael J. Wysocki
2016-02-05 9:49 ` Viresh Kumar
2016-02-08 2:20 ` Rafael J. Wysocki
2016-02-06 2:22 ` Saravana Kannan
2016-02-08 2:28 ` Rafael J. Wysocki
2016-02-09 21:02 ` Saravana Kannan
2016-02-04 6:24 ` Viresh Kumar
2016-02-04 12:17 ` Viresh Kumar
2016-02-04 20:50 ` Shilpasri G Bhat
2016-02-05 2:49 ` Viresh Kumar
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