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SubjectRe: [PATCH 35/51] acpi-cpufreq: Fix CPU hotplug callback registration
On 02/06/2014 06:13 PM, Rafael J. Wysocki wrote:
> 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?
>

Thank you! Same here, every patch depends only on the first patch in
the series. (Except the raid5 and the xen/balloon patches which don't
have any dependency).

But I'll be posting a v2 of this patchset soon with a rename of the
API..

Regards,
Srivatsa S. Bhat

>> ---
>>
>> 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
>


--
Regards,
Srivatsa S. Bhat



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