Subject: stomp-machine-raw-lock.patch
From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 29 Jun 2011 11:01:51 +0200

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 kernel/stop_machine.c |   58 +++++++++++++++++++++++++++++++++++---------------
 1 file changed, 41 insertions(+), 17 deletions(-)

Index: linux-stable/kernel/stop_machine.c
===================================================================
--- linux-stable.orig/kernel/stop_machine.c
+++ linux-stable/kernel/stop_machine.c
@@ -29,12 +29,12 @@ struct cpu_stop_done {
 	atomic_t		nr_todo;	/* nr left to execute */
 	bool			executed;	/* actually executed? */
 	int			ret;		/* collected return value */
-	struct completion	completion;	/* fired if nr_todo reaches 0 */
+	struct task_struct	*waiter;	/* woken when nr_todo reaches 0 */
 };
 
 /* the actual stopper, one per every possible cpu, enabled on online cpus */
 struct cpu_stopper {
-	spinlock_t		lock;
+	raw_spinlock_t		lock;
 	bool			enabled;	/* is this stopper enabled? */
 	struct list_head	works;		/* list of pending works */
 	struct task_struct	*thread;	/* stopper thread */
@@ -47,7 +47,7 @@ static void cpu_stop_init_done(struct cp
 {
 	memset(done, 0, sizeof(*done));
 	atomic_set(&done->nr_todo, nr_todo);
-	init_completion(&done->completion);
+	done->waiter = current;
 }
 
 /* signal completion unless @done is NULL */
@@ -56,8 +56,10 @@ static void cpu_stop_signal_done(struct 
 	if (done) {
 		if (executed)
 			done->executed = true;
-		if (atomic_dec_and_test(&done->nr_todo))
-			complete(&done->completion);
+		if (atomic_dec_and_test(&done->nr_todo)) {
+			wake_up_process(done->waiter);
+			done->waiter = NULL;
+		}
 	}
 }
 
@@ -67,7 +69,7 @@ static void cpu_stop_queue_work(struct c
 {
 	unsigned long flags;
 
-	spin_lock_irqsave(&stopper->lock, flags);
+	raw_spin_lock_irqsave(&stopper->lock, flags);
 
 	if (stopper->enabled) {
 		list_add_tail(&work->list, &stopper->works);
@@ -75,7 +77,23 @@ static void cpu_stop_queue_work(struct c
 	} else
 		cpu_stop_signal_done(work->done, false);
 
-	spin_unlock_irqrestore(&stopper->lock, flags);
+	raw_spin_unlock_irqrestore(&stopper->lock, flags);
+}
+
+static void wait_for_stop_done(struct cpu_stop_done *done)
+{
+	set_current_state(TASK_UNINTERRUPTIBLE);
+	while (atomic_read(&done->nr_todo)) {
+		schedule();
+		set_current_state(TASK_UNINTERRUPTIBLE);
+	}
+	/*
+	 * We need to wait until cpu_stop_signal_done() has cleared
+	 * done->waiter.
+	 */
+	while (done->waiter)
+		cpu_relax();
+	set_current_state(TASK_RUNNING);
 }
 
 /**
@@ -109,7 +127,7 @@ int stop_one_cpu(unsigned int cpu, cpu_s
 
 	cpu_stop_init_done(&done, 1);
 	cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), &work);
-	wait_for_completion(&done.completion);
+	wait_for_stop_done(&done);
 	return done.executed ? done.ret : -ENOENT;
 }
 
@@ -171,7 +189,7 @@ static int __stop_cpus(const struct cpum
 
 	cpu_stop_init_done(&done, cpumask_weight(cpumask));
 	queue_stop_cpus_work(cpumask, fn, arg, &done);
-	wait_for_completion(&done.completion);
+	wait_for_stop_done(&done);
 	return done.executed ? done.ret : -ENOENT;
 }
 
@@ -259,13 +277,13 @@ repeat:
 	}
 
 	work = NULL;
-	spin_lock_irq(&stopper->lock);
+	raw_spin_lock_irq(&stopper->lock);
 	if (!list_empty(&stopper->works)) {
 		work = list_first_entry(&stopper->works,
 					struct cpu_stop_work, list);
 		list_del_init(&work->list);
 	}
-	spin_unlock_irq(&stopper->lock);
+	raw_spin_unlock_irq(&stopper->lock);
 
 	if (work) {
 		cpu_stop_fn_t fn = work->fn;
@@ -299,7 +317,13 @@ repeat:
 			  kallsyms_lookup((unsigned long)fn, NULL, NULL, NULL,
 					  ksym_buf), arg);
 
+		/*
+		 * Make sure that the wakeup and setting done->waiter
+		 * to NULL is atomic.
+		 */
+		local_irq_disable();
 		cpu_stop_signal_done(done, true);
+		local_irq_enable();
 	} else
 		schedule();
 
@@ -337,9 +361,9 @@ static int __cpuinit cpu_stop_cpu_callba
 		/* strictly unnecessary, as first user will wake it */
 		wake_up_process(stopper->thread);
 		/* mark enabled */
-		spin_lock_irq(&stopper->lock);
+		raw_spin_lock_irq(&stopper->lock);
 		stopper->enabled = true;
-		spin_unlock_irq(&stopper->lock);
+		raw_spin_unlock_irq(&stopper->lock);
 		break;
 
 #ifdef CONFIG_HOTPLUG_CPU
@@ -352,11 +376,11 @@ static int __cpuinit cpu_stop_cpu_callba
 		/* kill the stopper */
 		kthread_stop(stopper->thread);
 		/* drain remaining works */
-		spin_lock_irq(&stopper->lock);
+		raw_spin_lock_irq(&stopper->lock);
 		list_for_each_entry(work, &stopper->works, list)
 			cpu_stop_signal_done(work->done, false);
 		stopper->enabled = false;
-		spin_unlock_irq(&stopper->lock);
+		raw_spin_unlock_irq(&stopper->lock);
 		/* release the stopper */
 		put_task_struct(stopper->thread);
 		stopper->thread = NULL;
@@ -387,7 +411,7 @@ static int __init cpu_stop_init(void)
 	for_each_possible_cpu(cpu) {
 		struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
 
-		spin_lock_init(&stopper->lock);
+		raw_spin_lock_init(&stopper->lock);
 		INIT_LIST_HEAD(&stopper->works);
 	}
 
@@ -581,7 +605,7 @@ int stop_machine_from_inactive_cpu(int (
 	ret = stop_machine_cpu_stop(&smdata);
 
 	/* Busy wait for completion. */
-	while (!completion_done(&done.completion))
+	while (atomic_read(&done.nr_todo))
 		cpu_relax();
 
 	mutex_unlock(&stop_cpus_mutex);