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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();
    > }
    > }
    >
    >
    > --
    > To unsubscribe from this list: send the line "unsubscribe cpufreq" in
    > the body of a message to majordomo@vger.kernel.org
    > More majordomo info at http://vger.kernel.org/majordomo-info.html

    --
    I speak only for myself.
    Rafael J. Wysocki, Intel Open Source Technology Center.


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