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SubjectRe: [PATCH 38/51] intel-idle: Fix CPU hotplug callback registration
On 02/06/2014 06:13 PM, Rafael J. Wysocki wrote:
> On Thursday, February 06, 2014 03:41:23 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 intel-idle code by using this latter form of callback registration.
>>
>> Cc: Len Brown <lenb@kernel.org>
>> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
>> Cc: linux-pm@vger.kernel.org
>> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
>
> This looks good to me. Len, what do you think?
>

Thanks a lot Rafael!

> Srivatsa, how does it depend on the rest of your series?
>

It depends only on the first patch in the series:
http://article.gmane.org/gmane.linux.kernel/1641640

But don't take this patch yet, we are discussing a possible rename
of the function cpu_maps_update_begin()/done(). So I'll post a v2
after the name is finalized.

Thank you!

Regards,
Srivatsa S. Bhat







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