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Commit e9b4ad84 authored by Srivatsa S. Bhat's avatar Srivatsa S. Bhat Committed by Matt Wagantall
Browse files

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>
Cc: netdev@vger.kernel.org
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Git-commit: e30a293e8ad7e6048d6d88bcc114094f964bd67b
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


[osvaldob@codeaurora.org: remove use of {get,put}_online_cpus()]
Signed-off-by: default avatarOsvaldo Banuelos <osvaldob@codeaurora.org>
parent 89396388

net/core/flow.c

+7 −4
Original line number Diff line number Diff line
@@ -456,7 +456,8 @@ static int __init flow_cache_init(struct flow_cache *fc) 
	if (!fc->percpu)

		return -ENOMEM;



	get_online_cpus();

	cpu_notifier_register_begin();



	for_each_online_cpu(i) {

		if (flow_cache_cpu_prepare(fc, i))

			goto err;
@@ -464,8 +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);

	put_online_cpus();

	__register_hotcpu_notifier(&fc->hotcpu_notifier);



	cpu_notifier_register_done();



	setup_timer(&fc->rnd_timer, flow_cache_new_hashrnd,

		    (unsigned long) fc);
@@ -475,13 +477,14 @@ static int __init flow_cache_init(struct flow_cache *fc) 
	return 0;



err:

	put_online_cpus();

	for_each_possible_cpu(i) {

		struct flow_cache_percpu *fcp = per_cpu_ptr(fc->percpu, i);

		kfree(fcp->hash_table);

		fcp->hash_table = NULL;

	}



	cpu_notifier_register_done();



	free_percpu(fc->percpu);

	fc->percpu = NULL;