From fe22ca5ca9e5d5b5fa6742b7ad40986c8389f155 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Tue, 20 Jul 2010 14:30:57 +0200
Subject: [PATCH] cpu-hotplug: Don't wake up the desched thread from idle_task_exit()

commit 8e7dbdf187d6a6896873a32537fed62111a5910e in tip.

When idle tasks exits then we do not want to wake the cpu bound
desched thread.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index b4f912f..631c0af 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2286,7 +2286,7 @@ extern struct mm_struct * mm_alloc(void);
 
 /* mmdrop drops the mm and the page tables */
 extern void __mmdrop(struct mm_struct *);
-extern void __mmdrop_delayed(struct mm_struct *);
+extern void __mmdrop_delayed(struct mm_struct *, int wake);
 
 static inline void mmdrop(struct mm_struct * mm)
 {
@@ -2294,10 +2294,10 @@ static inline void mmdrop(struct mm_struct * mm)
 		__mmdrop(mm);
 }
 
-static inline void mmdrop_delayed(struct mm_struct * mm)
+static inline void mmdrop_delayed(struct mm_struct * mm, int wake)
 {
 	if (atomic_dec_and_test(&mm->mm_count))
-		__mmdrop_delayed(mm);
+		__mmdrop_delayed(mm, wake);
 }
 
 /* mmput gets rid of the mappings and all user-space */
diff --git a/kernel/fork.c b/kernel/fork.c
index 6dc8e27..74192aa 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1805,24 +1805,26 @@ int unshare_files(struct files_struct **displaced)
 	return 0;
 }
 
-static int mmdrop_complete(void)
+static int mmdrop_complete(int cpu)
 {
 	struct list_head *head;
 	int ret = 0;
 
-	head = &get_cpu_var(delayed_drop_list);
+	preempt_disable();
+	head = &per_cpu(delayed_drop_list, cpu);
 	while (!list_empty(head)) {
 		struct mm_struct *mm = list_entry(head->next,
 					struct mm_struct, delayed_drop);
 		list_del(&mm->delayed_drop);
-		put_cpu_var(delayed_drop_list);
+		preempt_enable();
 
 		__mmdrop(mm);
 		ret = 1;
 
-		head = &get_cpu_var(delayed_drop_list);
+		preempt_disable();
+		head = &per_cpu(delayed_drop_list, cpu);
 	}
-	put_cpu_var(delayed_drop_list);
+	preempt_enable();
 
 	return ret;
 }
@@ -1831,7 +1833,7 @@ static int mmdrop_complete(void)
  * We dont want to do complex work from the scheduler, thus
  * we delay the work to a per-CPU worker thread:
  */
-void  __mmdrop_delayed(struct mm_struct *mm)
+void  __mmdrop_delayed(struct mm_struct *mm, int wake)
 {
 	struct task_struct *cpu_desched_task;
 	struct list_head *head;
@@ -1839,7 +1841,7 @@ void  __mmdrop_delayed(struct mm_struct *mm)
 	head = &get_cpu_var(delayed_drop_list);
 	list_add_tail(&mm->delayed_drop, head);
 	cpu_desched_task = __get_cpu_var(desched_task);
-	if (cpu_desched_task)
+	if (cpu_desched_task && wake)
 		wake_up_process(cpu_desched_task);
 	put_cpu_var(delayed_drop_list);
 }
@@ -1854,13 +1856,16 @@ static void takeover_delayed_drop(int hotcpu)
 				struct mm_struct, delayed_drop);
 
 		list_del(&mm->delayed_drop);
-		__mmdrop_delayed(mm);
+		__mmdrop_delayed(mm, 1);
 	}
 }
 #endif
 
 static int desched_thread(void * __bind_cpu)
 {
+
+	int cpu = (unsigned long)__bind_cpu;
+
 	set_user_nice(current, -10);
 	current->flags |= PF_NOFREEZE;
 	current->extra_flags |= PFE_SOFTIRQ;
@@ -1869,7 +1874,7 @@ static int desched_thread(void * __bind_cpu)
 
 	while (!kthread_should_stop()) {
 
-		if (mmdrop_complete())
+		if (mmdrop_complete(cpu))
 			continue;
 		schedule();
 
diff --git a/kernel/sched.c b/kernel/sched.c
index f03f1d2..f8557a5 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2939,7 +2939,7 @@ static void finish_task_switch(struct rq *rq, struct task_struct *prev)
 	 * to do complex work from within the scheduler:
 	 */
 	if (mm)
-		mmdrop_delayed(mm);
+		mmdrop_delayed(mm, 1);
 	if (unlikely(prev_state == TASK_DEAD)) {
 		/*
 		 * Remove function-return probe instances associated with this
@@ -7787,7 +7787,7 @@ void idle_task_exit(void)
 	if (mm != &init_mm)
 		switch_mm(mm, &init_mm, current);
 #ifdef CONFIG_PREEMPT_RT
-	mmdrop_delayed(mm);
+	mmdrop_delayed(mm, 0);
 #else
 	mmdrop(mm);
 #endif
-- 
1.7.1.1