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Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups

From Viresh Kumar <viresh.kumar@linaro.org>
Newsgroups linux.kernel
Subject Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups
Date 2016-02-05 03:50 +0100
Message-ID <qYED8-2lp-27@gated-at.bofh.it> (permalink)
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On 04-02-16, 19:18, Rafael J. Wysocki wrote:
> On Thu, Feb 4, 2016 at 6:44 PM, Saravana Kannan <skannan@codeaurora.org> wrote:
> > On 02/04/2016 09:43 AM, Saravana Kannan wrote:

> >> No no no no! Let's not open up this can of worms of queuing up the work
> >> to handle a write to a sysfs file. It *MIGHT* work for this specific
> >> tunable (I haven't bothered to analyze), but this makes it impossible to
> >> return a useful/proper error value.
> >
> >
> > Sent too soon. Not only that, but it can also cause the writes to the sysfs
> > files to get processed in a different order and I don't know what other
> > issues/races THAT will open up.
> 
> Well, I don't like this too.

I expected similar responses only, so no surprises for me :)

Though there are few things I would like to tell here:
- There wouldn't be any race for updating the file, as that is done
  directly from store_sampling_rate(). It updates the *real* file we
  wanted to.

- What's offloaded to the work-handler is something very special about
  ondemand governor and sampling rate. The same is not done for
  conservative governor as well, don't know why though.

- After updating the sampling rate, we assess if we need to reschedule
  the timers/workqueue to a different time for better efficiency. I
  don't think there can be a race there and it can be safely done in a
  work..

> I actually do have an idea about how to fix these deadlocks, but it is
> on top of my cleanup series.

I would like to hear that, if you can, to save your time. I have tried
so many different ways of fixing this yesterday and found issue
everywhere :(

-- 
viresh

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[PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups Viresh Kumar <viresh.kumar@linaro.org> - 2016-02-03 15:10 +0100
  [PATCH V2 4/7] Revert "cpufreq: Drop rwsem lock around CPUFREQ_GOV_POLICY_EXIT" Viresh Kumar <viresh.kumar@linaro.org> - 2016-02-03 15:10 +0100
  Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups Juri Lelli <juri.lelli@arm.com> - 2016-02-03 17:00 +0100
    Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups Viresh Kumar <viresh.kumar@linaro.org> - 2016-02-03 17:20 +0100
      Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups Juri Lelli <juri.lelli@arm.com> - 2016-02-03 18:20 +0100
        Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups "Rafael J. Wysocki" <rafael@kernel.org> - 2016-02-03 18:30 +0100
          Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups Shilpa Bhat <shilpabhatppc@gmail.com> - 2016-02-04 00:40 +0100
            Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups "Rafael J. Wysocki" <rafael@kernel.org> - 2016-02-04 01:00 +0100
              Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups Viresh Kumar <viresh.kumar@linaro.org> - 2016-02-04 07:00 +0100
              Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups Viresh Kumar <viresh.kumar@linaro.org> - 2016-02-04 12:10 +0100
                Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups Saravana Kannan <skannan@codeaurora.org> - 2016-02-04 18:50 +0100
                Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups Saravana Kannan <skannan@codeaurora.org> - 2016-02-04 18:50 +0100
                Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups "Rafael J. Wysocki" <rafael@kernel.org> - 2016-02-04 19:20 +0100
                Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups Viresh Kumar <viresh.kumar@linaro.org> - 2016-02-05 03:50 +0100
                Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-02-05 05:00 +0100
                Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups Viresh Kumar <viresh.kumar@linaro.org> - 2016-02-05 10:50 +0100
                Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-02-08 03:20 +0100
                Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups Saravana Kannan <skannan@codeaurora.org> - 2016-02-06 03:30 +0100
                Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-02-08 03:30 +0100
      Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups Viresh Kumar <viresh.kumar@linaro.org> - 2016-02-04 07:30 +0100
        Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups Viresh Kumar <viresh.kumar@linaro.org> - 2016-02-04 13:20 +0100
          Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com> - 2016-02-04 22:00 +0100
            Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups Viresh Kumar <viresh.kumar@linaro.org> - 2016-02-05 03:50 +0100

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