[PATCH 36/51] drivers/base/topology.c: Fix CPU hotplug callbackregistration

From: Srivatsa S. Bhat
Date: Wed Feb 05 2014 - 17:16:41 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_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 topology code by using this latter form of callback registration.

Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
---

drivers/base/topology.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/base/topology.c b/drivers/base/topology.c
index 94ffee3..9db29cc 100644
--- a/drivers/base/topology.c
+++ b/drivers/base/topology.c
@@ -161,16 +161,20 @@ static int topology_cpu_callback(struct notifier_block *nfb,
static int topology_sysfs_init(void)
{
int cpu;
- int rc;
+ int rc = 0;
+
+ cpu_maps_update_begin();

for_each_online_cpu(cpu) {
rc = topology_add_dev(cpu);
if (rc)
- return rc;
+ goto out;
}
- hotcpu_notifier(topology_cpu_callback, 0);
+ __hotcpu_notifier(topology_cpu_callback, 0);

- return 0;
+out:
+ cpu_maps_update_done();
+ return rc;
}

device_initcall(topology_sysfs_init);

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