| From | "Srivatsa S. Bhat" <> | Subject | [PATCH 50/51] net/core/flow.c: Fix CPU hotplug callback registration | Date | Thu, 06 Feb 2014 03:43:46 +0530 |
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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_maps_update_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_maps_update_done();
Fix the code in net/core/flow.c by using this latter form of callback registration.
Cc: "David S. Miller" <davem@davemloft.net> 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: netdev@vger.kernel.org Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> ---
net/core/flow.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/net/core/flow.c b/net/core/flow.c index dfa602c..0f2c995 100644 --- a/net/core/flow.c +++ b/net/core/flow.c @@ -456,6 +456,8 @@ static int __init flow_cache_init(struct flow_cache *fc) if (!fc->percpu) return -ENOMEM; + cpu_maps_update_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_maps_update_done(); setup_timer(&fc->rnd_timer, flow_cache_new_hashrnd, (unsigned long) fc); @@ -479,6 +483,8 @@ err: fcp->hash_table = NULL; } + cpu_maps_update_done(); + free_percpu(fc->percpu); fc->percpu = NULL;
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