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net/core/flow.c: Fix CPU hotplug callback registration 

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 code in net/core/flow.c by using this latter form of callback
registration.

Cc: Li RongQing <roy.qing.li@gmail.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Ingo Molnar <mingo@kernel.org>
Acked-by: David S. Miller <davem@davemloft.net>
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 02:12:51 +05:30 committed by Rafael J. Wysocki
parent 576378249c
commit e30a293e8a
1 changed files with 7 additions and 1 deletions
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8
net/core/flow.c
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@ -456,6 +456,8 @@ static int __init flow_cache_init(struct flow_cache *fc)
if (!fc->percpu)
return -ENOMEM;
cpu_notifier_register_begin();
for_each_online_cpu(i) {
if (flow_cache_cpu_prepare(fc, i))
goto err;
@ -463,7 +465,9 @@ static int __init flow_cache_init(struct flow_cache *fc)
fc->hotcpu_notifier = (struct notifier_block){
.notifier_call = flow_cache_cpu,
};
register_hotcpu_notifier(&fc->hotcpu_notifier);
__register_hotcpu_notifier(&fc->hotcpu_notifier);
cpu_notifier_register_done();
setup_timer(&fc->rnd_timer, flow_cache_new_hashrnd,
(unsigned long) fc);
@ -479,6 +483,8 @@ static int __init flow_cache_init(struct flow_cache *fc)
fcp->hash_table = NULL;
}
cpu_notifier_register_done();
free_percpu(fc->percpu);
fc->percpu = NULL;