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SubjectRe: [PATCH v3 36/52] zsmalloc: Fix CPU hotplug callback registration
On Tue, Mar 11, 2014 at 02:09:59AM +0530, 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_notifier_register_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_notifier_register_done();
>
>
> Fix the zsmalloc code by using this latter form of callback registration.
>
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: Nitin Gupta <ngupta@vflare.org>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: linux-mm@kvack.org
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>

Acked-by: Minchan Kim <minchan@kernel.org>

Thanks.

--
Kind regards,
Minchan Kim


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