[PATCH 41/51] thermal,x86-pkg-temp: Fix CPU hotplug callback registration

From: Srivatsa S. Bhat
Date: Wed Feb 05 2014 - 17:17:29 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 thermal x86-pkg-temp code by using this latter form of callback
registration.

Cc: Zhang Rui <rui.zhang@xxxxxxxxx>
Cc: Eduardo Valentin <eduardo.valentin@xxxxxx>
Cc: linux-pm@xxxxxxxxxxxxxxx
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
---

drivers/thermal/x86_pkg_temp_thermal.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/thermal/x86_pkg_temp_thermal.c b/drivers/thermal/x86_pkg_temp_thermal.c
index 972e1c7..55f9eac 100644
--- a/drivers/thermal/x86_pkg_temp_thermal.c
+++ b/drivers/thermal/x86_pkg_temp_thermal.c
@@ -589,12 +589,12 @@ static int __init pkg_temp_thermal_init(void)
platform_thermal_package_rate_control =
pkg_temp_thermal_platform_thermal_rate_control;

- get_online_cpus();
+ cpu_maps_update_begin();
for_each_online_cpu(i)
if (get_core_online(i))
goto err_ret;
- register_hotcpu_notifier(&pkg_temp_thermal_notifier);
- put_online_cpus();
+ __register_hotcpu_notifier(&pkg_temp_thermal_notifier);
+ cpu_maps_update_done();

pkg_temp_debugfs_init(); /* Don't care if fails */

@@ -603,7 +603,7 @@ static int __init pkg_temp_thermal_init(void)
err_ret:
for_each_online_cpu(i)
put_core_offline(i);
- put_online_cpus();
+ cpu_maps_update_done();
kfree(pkg_work_scheduled);
platform_thermal_package_notify = NULL;
platform_thermal_package_rate_control = NULL;
@@ -616,8 +616,8 @@ static void __exit pkg_temp_thermal_exit(void)
struct phy_dev_entry *phdev, *n;
int i;

- get_online_cpus();
- unregister_hotcpu_notifier(&pkg_temp_thermal_notifier);
+ cpu_maps_update_begin();
+ __unregister_hotcpu_notifier(&pkg_temp_thermal_notifier);
mutex_lock(&phy_dev_list_mutex);
list_for_each_entry_safe(phdev, n, &phy_dev_list, list) {
/* Retore old MSR value for package thermal interrupt */
@@ -635,7 +635,7 @@ static void __exit pkg_temp_thermal_exit(void)
for_each_online_cpu(i)
cancel_delayed_work_sync(
&per_cpu(pkg_temp_thermal_threshold_work, i));
- put_online_cpus();
+ cpu_maps_update_done();

kfree(pkg_work_scheduled);


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