Merge tag 'v3.18' into p/abusse/merge_upgrade
[projects/modsched/linux.git] / kernel / cpu.c
index e6702fa..feff739 100644 (file)
@@ -68,6 +68,8 @@ static struct {
         * an ongoing cpu hotplug operation.
         */
        int refcount;
+       /* And allows lockless put_online_cpus(). */
+       atomic_t puts_pending;
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
        struct lockdep_map dep_map;
@@ -83,6 +85,8 @@ static struct {
 
 /* Lockdep annotations for get/put_online_cpus() and cpu_hotplug_begin/end() */
 #define cpuhp_lock_acquire_read() lock_map_acquire_read(&cpu_hotplug.dep_map)
+#define cpuhp_lock_acquire_tryread() \
+                                 lock_map_acquire_tryread(&cpu_hotplug.dep_map)
 #define cpuhp_lock_acquire()      lock_map_acquire(&cpu_hotplug.dep_map)
 #define cpuhp_lock_release()      lock_map_release(&cpu_hotplug.dep_map)
 
@@ -95,15 +99,31 @@ void get_online_cpus(void)
        mutex_lock(&cpu_hotplug.lock);
        cpu_hotplug.refcount++;
        mutex_unlock(&cpu_hotplug.lock);
-
 }
 EXPORT_SYMBOL_GPL(get_online_cpus);
 
+bool try_get_online_cpus(void)
+{
+       if (cpu_hotplug.active_writer == current)
+               return true;
+       if (!mutex_trylock(&cpu_hotplug.lock))
+               return false;
+       cpuhp_lock_acquire_tryread();
+       cpu_hotplug.refcount++;
+       mutex_unlock(&cpu_hotplug.lock);
+       return true;
+}
+EXPORT_SYMBOL_GPL(try_get_online_cpus);
+
 void put_online_cpus(void)
 {
        if (cpu_hotplug.active_writer == current)
                return;
-       mutex_lock(&cpu_hotplug.lock);
+       if (!mutex_trylock(&cpu_hotplug.lock)) {
+               atomic_inc(&cpu_hotplug.puts_pending);
+               cpuhp_lock_release();
+               return;
+       }
 
        if (WARN_ON(!cpu_hotplug.refcount))
                cpu_hotplug.refcount++; /* try to fix things up */
@@ -145,6 +165,12 @@ void cpu_hotplug_begin(void)
        cpuhp_lock_acquire();
        for (;;) {
                mutex_lock(&cpu_hotplug.lock);
+               if (atomic_read(&cpu_hotplug.puts_pending)) {
+                       int delta;
+
+                       delta = atomic_xchg(&cpu_hotplug.puts_pending, 0);
+                       cpu_hotplug.refcount -= delta;
+               }
                if (likely(!cpu_hotplug.refcount))
                        break;
                __set_current_state(TASK_UNINTERRUPTIBLE);