Re: [PATCH 48/51] mm, vmstat: Fix CPU hotplug callback registration

[Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>]

(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);
>


--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>