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

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Date:	Fri, 7 Feb 2014 11:52:05 +0900
From:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
CC:	<paulus@...ba.org>, <oleg@...hat.com>, <rusty@...tcorp.com.au>,
	<peterz@...radead.org>, <tglx@...utronix.de>,
	<akpm@...ux-foundation.org>, <mingo@...nel.org>,
	<paulmck@...ux.vnet.ibm.com>, <tj@...nel.org>, <walken@...gle.com>,
	<ego@...ux.vnet.ibm.com>, <linux@....linux.org.uk>,
	<linux-kernel@...r.kernel.org>, Christoph Lameter <cl@...ux.com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Cody P Schafer <cody@...ux.vnet.ibm.com>,
	Toshi Kani <toshi.kani@...com>, Dave Hansen <dave@...1.net>,
	<linux-mm@...ck.org>
Subject: Re: [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@...ux-foundation.org>
> Cc: Christoph Lameter <cl@...ux.com>
> Cc: Rik van Riel <riel@...hat.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
> Cc: Cody P Schafer <cody@...ux.vnet.ibm.com>
> Cc: Toshi Kani <toshi.kani@...com>
> Cc: Dave Hansen <dave@...1.net>
> Cc: linux-mm@...ck.org
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
> ---

Looks good to me.

Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@...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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