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mm, zswap: Fix CPU hotplug callback registration

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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 zswap code by using this latter form of callback registration.

Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Srivatsa S. Bhat 2014-03-11 02:12:40 +05:30 committed by Rafael J. Wysocki
parent 0be94bad0b
commit 576378249c
1 changed files with 4 additions and 4 deletions
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8
mm/zswap.c
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@ -387,18 +387,18 @@ static int zswap_cpu_init(void)
{
unsigned long cpu;
get_online_cpus();
cpu_notifier_register_begin();
for_each_online_cpu(cpu)
if (__zswap_cpu_notifier(CPU_UP_PREPARE, cpu) != NOTIFY_OK)
goto cleanup;
register_cpu_notifier(&zswap_cpu_notifier_block);
put_online_cpus();
__register_cpu_notifier(&zswap_cpu_notifier_block);
cpu_notifier_register_done();
return 0;
cleanup:
for_each_online_cpu(cpu)
__zswap_cpu_notifier(CPU_UP_CANCELED, cpu);
put_online_cpus();
cpu_notifier_register_done();
return -ENOMEM;
}