[PATCH v3 07/52] ia64, topology: Fix CPU hotplug callback registration

From: Srivatsa S. Bhat
Date: Mon Mar 10 2014 - 16:35:32 EST


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 topology code in ia64 by using this latter form of callback
registration.

Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: linux-ia64@xxxxxxxxxxxxxxx
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
---

arch/ia64/kernel/topology.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/ia64/kernel/topology.c b/arch/ia64/kernel/topology.c
index ca69a5a..f295f9a 100644
--- a/arch/ia64/kernel/topology.c
+++ b/arch/ia64/kernel/topology.c
@@ -454,12 +454,16 @@ static int __init cache_sysfs_init(void)
{
int i;

+ cpu_notifier_register_begin();
+
for_each_online_cpu(i) {
struct device *sys_dev = get_cpu_device((unsigned int)i);
cache_add_dev(sys_dev);
}

- register_hotcpu_notifier(&cache_cpu_notifier);
+ __register_hotcpu_notifier(&cache_cpu_notifier);
+
+ cpu_notifier_register_done();

return 0;
}

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