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SubjectRe: [PATCH 35/51] acpi-cpufreq: Fix CPU hotplug callback registration
Date
On Thursday, February 06, 2014 03:40:53 AM Srivatsa S. Bhat wrote:
> Subsystems that want to register CPU hotplug callbacks, as well as perform
> initialization for the CPUs that are already online, often do it as shown
> below:
>
> get_online_cpus();
>
> for_each_online_cpu(cpu)
> init_cpu(cpu);
>
> register_cpu_notifier(&foobar_cpu_notifier);
>
> put_online_cpus();
>
> This is wrong, since it is prone to ABBA deadlocks involving the
> cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
> with CPU hotplug operations).
>
> Instead, the correct and race-free way of performing the callback
> registration is:
>
> cpu_maps_update_begin();
>
> for_each_online_cpu(cpu)
> init_cpu(cpu);
>
> /* Note the use of the double underscored version of the API */
> __register_cpu_notifier(&foobar_cpu_notifier);
>
> cpu_maps_update_done();
>
>
> Fix the acpi-cpufreq code by using this latter form of callback registration.
>
> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> Cc: Viresh Kumar <viresh.kumar@linaro.org>
> Cc: cpufreq@vger.kernel.org
> Cc: linux-pm@vger.kernel.org
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>

Looks OK to me. How does it depend on the rest of your series?

> ---
>
> drivers/cpufreq/acpi-cpufreq.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
> index 18448a7..e2eb471 100644
> --- a/drivers/cpufreq/acpi-cpufreq.c
> +++ b/drivers/cpufreq/acpi-cpufreq.c
> @@ -907,15 +907,16 @@ static void __init acpi_cpufreq_boost_init(void)
>
> acpi_cpufreq_driver.boost_supported = true;
> acpi_cpufreq_driver.boost_enabled = boost_state(0);
> - get_online_cpus();
> +
> + cpu_maps_update_begin();
>
> /* Force all MSRs to the same value */
> boost_set_msrs(acpi_cpufreq_driver.boost_enabled,
> cpu_online_mask);
>
> - register_cpu_notifier(&boost_nb);
> + __register_cpu_notifier(&boost_nb);
>
> - put_online_cpus();
> + cpu_maps_update_done();
> }
> }
>
>
> --
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--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.


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