14 files changed, 391 insertions, 501 deletions

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 5d220234b3ca..1972b161c61e 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -58,22 +58,23 @@ static int cpu_hotplug_disabled;
 
 static struct {
         struct task_struct *active_writer;
-        struct mutex lock; /* Synchronizes accesses to refcount, */
+        /* wait queue to wake up the active_writer */
+        wait_queue_head_t wq;
+        /* verifies that no writer will get active while readers are active */
+        struct mutex lock;
         /*
          * Also blocks the new readers during
          * an ongoing cpu hotplug operation.
          */
-        int refcount;
-        /* And allows lockless put_online_cpus(). */
-        atomic_t puts_pending;
+        atomic_t refcount;
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
         struct lockdep_map dep_map;
 #endif
 } cpu_hotplug = {
         .active_writer = NULL,
+        .wq = __WAIT_QUEUE_HEAD_INITIALIZER(cpu_hotplug.wq),
         .lock = __MUTEX_INITIALIZER(cpu_hotplug.lock),
-        .refcount = 0,
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
         .dep_map = {.name = "cpu_hotplug.lock" },
 #endif
@@ -86,15 +87,6 @@ static struct {
 #define cpuhp_lock_acquire()      lock_map_acquire(&cpu_hotplug.dep_map)
 #define cpuhp_lock_release()      lock_map_release(&cpu_hotplug.dep_map)
 
-static void apply_puts_pending(int max)
-{
-        int delta;
-
-        if (atomic_read(&cpu_hotplug.puts_pending) >= max) {
-                delta = atomic_xchg(&cpu_hotplug.puts_pending, 0);
-                cpu_hotplug.refcount -= delta;
-        }
-}
 
 void get_online_cpus(void)
 {
@@ -103,8 +95,7 @@ void get_online_cpus(void)
                 return;
         cpuhp_lock_acquire_read();
         mutex_lock(&cpu_hotplug.lock);
-        apply_puts_pending(65536);
-        cpu_hotplug.refcount++;
+        atomic_inc(&cpu_hotplug.refcount);
         mutex_unlock(&cpu_hotplug.lock);
 }
 EXPORT_SYMBOL_GPL(get_online_cpus);
@@ -116,8 +107,7 @@ bool try_get_online_cpus(void)
         if (!mutex_trylock(&cpu_hotplug.lock))
                 return false;
         cpuhp_lock_acquire_tryread();
-        apply_puts_pending(65536);
-        cpu_hotplug.refcount++;
+        atomic_inc(&cpu_hotplug.refcount);
         mutex_unlock(&cpu_hotplug.lock);
         return true;
 }
@@ -125,20 +115,18 @@ EXPORT_SYMBOL_GPL(try_get_online_cpus);
 
 void put_online_cpus(void)
 {
+        int refcount;
+
         if (cpu_hotplug.active_writer == current)
                 return;
-        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 */
+        refcount = atomic_dec_return(&cpu_hotplug.refcount);
+        if (WARN_ON(refcount < 0)) /* try to fix things up */
+                atomic_inc(&cpu_hotplug.refcount);
+
+        if (refcount <= 0 && waitqueue_active(&cpu_hotplug.wq))
+                wake_up(&cpu_hotplug.wq);
 
-        if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))
-                wake_up_process(cpu_hotplug.active_writer);
-        mutex_unlock(&cpu_hotplug.lock);
         cpuhp_lock_release();
 
 }
@@ -168,18 +156,20 @@ EXPORT_SYMBOL_GPL(put_online_cpus);
  */
 void cpu_hotplug_begin(void)
 {
-        cpu_hotplug.active_writer = current;
+        DEFINE_WAIT(wait);
 
+        cpu_hotplug.active_writer = current;
         cpuhp_lock_acquire();
+
         for (;;) {
                 mutex_lock(&cpu_hotplug.lock);
-                apply_puts_pending(1);
-                if (likely(!cpu_hotplug.refcount))
-                        break;
-                __set_current_state(TASK_UNINTERRUPTIBLE);
+                prepare_to_wait(&cpu_hotplug.wq, &wait, TASK_UNINTERRUPTIBLE);
+                if (likely(!atomic_read(&cpu_hotplug.refcount)))
+                                break;
                 mutex_unlock(&cpu_hotplug.lock);
                 schedule();
         }
+        finish_wait(&cpu_hotplug.wq, &wait);
 }
 
 void cpu_hotplug_done(void)
diff --git a/kernel/notifier.c b/kernel/notifier.c
index 4803da6eab62..ae9fc7cc360e 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -402,6 +402,7 @@ int raw_notifier_call_chain(struct raw_notifier_head *nh,
 }
 EXPORT_SYMBOL_GPL(raw_notifier_call_chain);
 
+#ifdef CONFIG_SRCU
 /*
  *      SRCU notifier chain routines.    Registration and unregistration
  *      use a mutex, and call_chain is synchronized by SRCU (no locks).
@@ -528,6 +529,8 @@ void srcu_init_notifier_head(struct srcu_notifier_head *nh)
 }
 EXPORT_SYMBOL_GPL(srcu_init_notifier_head);
 
+#endif /* CONFIG_SRCU */
+
 static ATOMIC_NOTIFIER_HEAD(die_chain);
 
 int notrace notify_die(enum die_val val, const char *str,
diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
index 48b28d387c7f..7e01f78f0417 100644
--- a/kernel/power/Kconfig
+++ b/kernel/power/Kconfig
@@ -251,6 +251,7 @@ config APM_EMULATION
 
 config PM_OPP
         bool
+        select SRCU
         ---help---
           SOCs have a standard set of tuples consisting of frequency and
           voltage pairs that the device will support per voltage domain. This
diff --git a/kernel/rcu/Makefile b/kernel/rcu/Makefile
index e6fae503d1bc..50a808424b06 100644
--- a/kernel/rcu/Makefile
+++ b/kernel/rcu/Makefile
@@ -1,4 +1,5 @@
-obj-y += update.o srcu.o
+obj-y += update.o
+obj-$(CONFIG_SRCU) += srcu.o
 obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
 obj-$(CONFIG_TREE_RCU) += tree.o
 obj-$(CONFIG_PREEMPT_RCU) += tree.o
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 07bb02eda844..80adef7d4c3d 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -137,4 +137,10 @@ int rcu_jiffies_till_stall_check(void);
 
 void rcu_early_boot_tests(void);
 
+/*
+ * This function really isn't for public consumption, but RCU is special in
+ * that context switches can allow the state machine to make progress.
+ */
+extern void resched_cpu(int cpu);
+
 #endif /* __LINUX_RCU_H */
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 4d559baf06e0..30d42aa55d83 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -244,7 +244,8 @@ struct rcu_torture_ops {