Re: [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 <redacted>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: linux-mm@kvack.org
Signed-off-by: Srivatsa S. Bhat <redacted>

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

Thanks.

-- 
Kind regards,
Minchan Kim