hwmon: (coretemp) Use get_online_cpus to avoid races involving CPU hotplug

coretemp_init loops with for_each_online_cpu, adding platform_devices
and sysfs interfaces, then calls register_hotcpu_notifier.  There is a
race if a CPU is offlined or onlined after the loop, but before
register_hotcpu_notifier.  The race might result in the absence of a
platform_device+sysfs interface for an online CPU, or the presence of
a platform_device+sysfs interface for an offline CPU.  A similar race
occurs during coretemp_exit, after the module calls
unregister_hotcpu_notifier, but before it unregisters all devices, a
CPU might offline and a device for an offline CPU will exist for a
short while.

This fix surrounds for_each_online_cpu and register_hotcpu_notifier
with get_online_cpus+put_online_cpus; and surrounds
unregister_hotcpu_notifier and device unregistering with
get_online_cpus+put_online_cpus.

Build tested.

Signed-off-by: Silas Boyd-Wickizer <sbw@mit.edu>
Signed-off-by: Jean Delvare <khali@linux-fr.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/hwmon/coretemp.c b/drivers/hwmon/coretemp.c
index 0fa356fe82cc..984a3f13923b 100644
--- a/drivers/hwmon/coretemp.c
+++ b/drivers/hwmon/coretemp.c
@@ -815,17 +815,20 @@ static int __init coretemp_init(void)
         if (err)
                 goto exit;
 
+        get_online_cpus();
         for_each_online_cpu(i)
                 get_core_online(i);
 
 #ifndef CONFIG_HOTPLUG_CPU
         if (list_empty(&pdev_list)) {
+                put_online_cpus();
                 err = -ENODEV;
                 goto exit_driver_unreg;
         }
 #endif
 
         register_hotcpu_notifier(&coretemp_cpu_notifier);
+        put_online_cpus();
         return 0;
 
 #ifndef CONFIG_HOTPLUG_CPU
@@ -840,6 +843,7 @@ static void __exit coretemp_exit(void)
 {
         struct pdev_entry *p, *n;
 
+        get_online_cpus();
         unregister_hotcpu_notifier(&coretemp_cpu_notifier);
         mutex_lock(&pdev_list_mutex);
         list_for_each_entry_safe(p, n, &pdev_list, list) {
@@ -848,6 +852,7 @@ static void __exit coretemp_exit(void)
                 kfree(p);
         }
         mutex_unlock(&pdev_list_mutex);
+        put_online_cpus();
         platform_driver_unregister(&coretemp_driver);
 }