Commit e30a293e authored Mar 11, 2014 by Srivatsa S. Bhat Committed by Rafael J. Wysocki Mar 20, 2014

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>

parent 57637824

net/core/flow.c

+7 −1

Original line number	Original line	Diff line number	Diff line
	@@ -456,6 +456,8 @@ static int __init flow_cache_init(struct flow_cache *fc)
	if (!fc->percpu)		if (!fc->percpu)
	return -ENOMEM;		return -ENOMEM;

			cpu_notifier_register_begin();

	for_each_online_cpu(i) {		for_each_online_cpu(i) {
	if (flow_cache_cpu_prepare(fc, i))		if (flow_cache_cpu_prepare(fc, i))
	goto err;		goto err;
	@@ -463,7 +465,9 @@ static int __init flow_cache_init(struct flow_cache *fc)
	fc->hotcpu_notifier = (struct notifier_block){		fc->hotcpu_notifier = (struct notifier_block){
	.notifier_call = flow_cache_cpu,		.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,		setup_timer(&fc->rnd_timer, flow_cache_new_hashrnd,
	(unsigned long) fc);		(unsigned long) fc);
	@@ -479,6 +483,8 @@ static int __init flow_cache_init(struct flow_cache *fc)
	fcp->hash_table = NULL;		fcp->hash_table = NULL;
	}		}

			cpu_notifier_register_done();

	free_percpu(fc->percpu);		free_percpu(fc->percpu);
	fc->percpu = NULL;		fc->percpu = NULL;