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SubjectRe: [PATCH 48/51] mm, vmstat: Fix CPU hotplug callback registration
(2014/02/06 7:13), 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 vmstat code in the MM subsystem by using this latter form of callback
> registration.
>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
> Cc: Cody P Schafer <cody@linux.vnet.ibm.com>
> Cc: Toshi Kani <toshi.kani@hp.com>
> Cc: Dave Hansen <dave@sr71.net>
> Cc: linux-mm@kvack.org
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
> ---

Looks good to me.

Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>

Thanks,
Yasuaki Ishimatsu


>
> mm/vmstat.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 7249614..70668ba 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1290,14 +1290,14 @@ static int __init setup_vmstat(void)
> #ifdef CONFIG_SMP
> int cpu;
>
> - register_cpu_notifier(&vmstat_notifier);
> + cpu_maps_update_begin();
> + __register_cpu_notifier(&vmstat_notifier);
>
> - get_online_cpus();
> for_each_online_cpu(cpu) {
> start_cpu_timer(cpu);
> node_set_state(cpu_to_node(cpu), N_CPU);
> }
> - put_online_cpus();
> + cpu_maps_update_done();
> #endif
> #ifdef CONFIG_PROC_FS
> proc_create("buddyinfo", S_IRUGO, NULL, &fragmentation_file_operations);
>




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