[PATCH v3 45/52] hwmon, via-cputemp: Fix CPU hotplug callback registration

From: Srivatsa S. Bhat
Date: Mon Mar 10 2014 - 16:41:59 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 hwmon via-cputemp code by using this latter form of callback
registration.

Cc: Jean Delvare <jdelvare@xxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: lm-sensors@xxxxxxxxxxxxxx
Acked-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
---

drivers/hwmon/via-cputemp.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/hwmon/via-cputemp.c b/drivers/hwmon/via-cputemp.c
index 38944e9..8df43c5 100644
--- a/drivers/hwmon/via-cputemp.c
+++ b/drivers/hwmon/via-cputemp.c
@@ -319,7 +319,7 @@ static int __init via_cputemp_init(void)
if (err)
goto exit;

- get_online_cpus();
+ cpu_notifier_register_begin();
for_each_online_cpu(i) {
struct cpuinfo_x86 *c = &cpu_data(i);

@@ -339,14 +339,14 @@ static int __init via_cputemp_init(void)

#ifndef CONFIG_HOTPLUG_CPU
if (list_empty(&pdev_list)) {
- put_online_cpus();
+ cpu_notifier_register_done();
err = -ENODEV;
goto exit_driver_unreg;
}
#endif

- register_hotcpu_notifier(&via_cputemp_cpu_notifier);
- put_online_cpus();
+ __register_hotcpu_notifier(&via_cputemp_cpu_notifier);
+ cpu_notifier_register_done();
return 0;

#ifndef CONFIG_HOTPLUG_CPU
@@ -361,8 +361,8 @@ static void __exit via_cputemp_exit(void)
{
struct pdev_entry *p, *n;

- get_online_cpus();
- unregister_hotcpu_notifier(&via_cputemp_cpu_notifier);
+ cpu_notifier_register_begin();
+ __unregister_hotcpu_notifier(&via_cputemp_cpu_notifier);
mutex_lock(&pdev_list_mutex);
list_for_each_entry_safe(p, n, &pdev_list, list) {
platform_device_unregister(p->pdev);
@@ -370,7 +370,7 @@ static void __exit via_cputemp_exit(void)
kfree(p);
}
mutex_unlock(&pdev_list_mutex);
- put_online_cpus();
+ cpu_notifier_register_done();
platform_driver_unregister(&via_cputemp_driver);
}


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