sched/core: Fix a race between try_to_wake_up() and a woken up task

[GitHub/mt8127/android_kernel_alcatel_ttab.git] / kernel / cpu.c

diff --git a/kernel/cpu.c b/kernel/cpu.c
index b5e4ab2d427e874404347c7e20186ed4cfd2f488..bc255e25d5ddced3bcda1cca7f2d61ba3e7c6cac 100644 (file)
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -133,6 +133,27 @@ static void cpu_hotplug_done(void)
        mutex_unlock(&cpu_hotplug.lock);
 }
 
+/*
+ * Wait for currently running CPU hotplug operations to complete (if any) and
+ * disable future CPU hotplug (from sysfs). The 'cpu_add_remove_lock' protects
+ * the 'cpu_hotplug_disabled' flag. The same lock is also acquired by the
+ * hotplug path before performing hotplug operations. So acquiring that lock
+ * guarantees mutual exclusion from any currently running hotplug operations.
+ */
+void cpu_hotplug_disable(void)
+{
+       cpu_maps_update_begin();
+       cpu_hotplug_disabled = 1;
+       cpu_maps_update_done();
+}
+
+void cpu_hotplug_enable(void)
+{
+       cpu_maps_update_begin();
+       cpu_hotplug_disabled = 0;
+       cpu_maps_update_done();
+}
+
 #else /* #if CONFIG_HOTPLUG_CPU */
 static void cpu_hotplug_begin(void) {}
 static void cpu_hotplug_done(void) {}
@@ -540,36 +561,6 @@ static int __init alloc_frozen_cpus(void)
 }
 core_initcall(alloc_frozen_cpus);
 
-/*
- * Prevent regular CPU hotplug from racing with the freezer, by disabling CPU
- * hotplug when tasks are about to be frozen. Also, don't allow the freezer
- * to continue until any currently running CPU hotplug operation gets
- * completed.
- * To modify the 'cpu_hotplug_disabled' flag, we need to acquire the
- * 'cpu_add_remove_lock'. And this same lock is also taken by the regular
- * CPU hotplug path and released only after it is complete. Thus, we
- * (and hence the freezer) will block here until any currently running CPU
- * hotplug operation gets completed.
- */
-void cpu_hotplug_disable_before_freeze(void)
-{
-       cpu_maps_update_begin();
-       cpu_hotplug_disabled = 1;
-       cpu_maps_update_done();
-}
-
-
-/*
- * When tasks have been thawed, re-enable regular CPU hotplug (which had been
- * disabled while beginning to freeze tasks).
- */
-void cpu_hotplug_enable_after_thaw(void)
-{
-       cpu_maps_update_begin();
-       cpu_hotplug_disabled = 0;
-       cpu_maps_update_done();
-}
-
 /*
  * When callbacks for CPU hotplug notifications are being executed, we must
  * ensure that the state of the system with respect to the tasks being frozen
@@ -589,12 +580,12 @@ cpu_hotplug_pm_callback(struct notifier_block *nb,
 
        case PM_SUSPEND_PREPARE:
        case PM_HIBERNATION_PREPARE:
-               cpu_hotplug_disable_before_freeze();
+               cpu_hotplug_disable();
                break;
 
        case PM_POST_SUSPEND:
        case PM_POST_HIBERNATION:
-               cpu_hotplug_enable_after_thaw();
+               cpu_hotplug_enable();
                break;
 
        default:
@@ -707,10 +698,12 @@ void set_cpu_present(unsigned int cpu, bool present)
 
 void set_cpu_online(unsigned int cpu, bool online)
 {
-       if (online)
+       if (online) {
                cpumask_set_cpu(cpu, to_cpumask(cpu_online_bits));
-       else
+               cpumask_set_cpu(cpu, to_cpumask(cpu_active_bits));
+       } else {
                cpumask_clear_cpu(cpu, to_cpumask(cpu_online_bits));
+       }
 }
 
 void set_cpu_active(unsigned int cpu, bool active)