linux-kernel - Re: [PATCH][RFC] cpufreq: Bring CPUs up even if cpufreq

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Date:   Mon, 27 Mar 2017 23:32:35 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Chen Yu <yu.c.chen@...el.com>
Cc:     Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Stable # 4 . 9+" <stable@...r.kernel.org>
Subject: Re: [PATCH][RFC] cpufreq: Bring CPUs up even if cpufreq_online failed

On Sat, Mar 25, 2017 at 5:20 AM, Chen Yu <yu.c.chen@...el.com> wrote:
> There is a report that after
> commit 27622b061eb4 ("cpufreq: Convert to hotplug state machine"),
> the normal CPU offline/online cycle failed on some platforms.
> According to the ftrace result, this problem was triggered on
> platforms using acpi-freq as the default cpufreq driver,
> and due to the lack of some ACPI freq method(_PCT eg), the
> cpufreq_online failed and returned a negative value, thus the cpu
> hotplug statemachine rollbacked the CPU online process. Actually
> the failure of cpufreq_online should not impact the whole CPU
> online process according to the original semantics before above patch.
> BTW, during system bootup the cpufreq_online is not invoked via
> cpuhotplug statemachine but by the cpufreq device creation process,
> thus the APs can be brought up although cpufreq_online failed in that
> stage.
>
> This patch ignores the return value of cpufreq_online/offline and
> prints a warning if there is a failure.
>
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=194581
> Fixes: 27622b061eb4 ("cpufreq: Convert to hotplug state machine")
> Reported-and-tested-by: Tomasz Maciej Nowak <tmn505@...il.com>
> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> Cc: Viresh Kumar <viresh.kumar@...aro.org>
> Cc: linux-pm@...r.kernel.org
> Cc: Stable <stable@...r.kernel.org> # 4.9+
> Signed-off-by: Chen Yu <yu.c.chen@...el.com>
> ---
>  drivers/cpufreq/cpufreq.c | 26 ++++++++++++++++++++++++--
>  1 file changed, 24 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index b8ff617..1c13873 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -2391,6 +2391,28 @@ EXPORT_SYMBOL_GPL(cpufreq_boost_enabled);
>   *********************************************************************/
>  static enum cpuhp_state hp_online;
>
> +static int cpuhp_cpufreq_online(unsigned int cpu)
> +{
> +       int ret = cpufreq_online(cpu);
> +
> +       if (ret)
> +               pr_err("Failed to bring cpufreq online for CPU%u. (%d)\n",
> +                       cpu, ret);

This pr_err() is not particularly useful IMO, because cpufreq_online()
complains on the majority of errors.

It would be better to make cpufreq_online() log errors with pr_err()
in all cases instead.

> +
> +       return 0;
> +}
> +
> +static int cpuhp_cpufreq_offline(unsigned int cpu)
> +{
> +       int ret = cpufreq_offline(cpu);
> +
> +       if (ret)
> +               pr_err("Failed to put cpufreq offline for CPU%u. (%d)\n",
> +                       cpu, ret);

And analogously here.

> +
> +       return 0;
> +}
> +
>  /**
>   * cpufreq_register_driver - register a CPU Frequency driver
>   * @driver_data: A struct cpufreq_driver containing the values#
> @@ -2453,8 +2475,8 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
>         }
>
>         ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "cpufreq:online",
> -                                       cpufreq_online,
> -                                       cpufreq_offline);
> +                                       cpuhp_cpufreq_online,
> +                                       cpuhp_cpufreq_offline);
>         if (ret < 0)
>                 goto err_if_unreg;
>         hp_online = ret;
> --
> 2.7.4

The rest looks OK to me.

Thanks,
Rafael