sched-make-task-oncpu-available-in-all-configuration.patch

From 89f3f6e92b72f07991b7f1e716ea3f97ccd5b2ba Mon Sep 17 00:00:00 2001
From: Gregory Haskins <ghaskins@novell.com>
Date: Fri, 3 Jul 2009 08:44:21 -0500
Subject: [PATCH] sched: make task->oncpu available in all configurations

commit 529d35d4c98a136eb811607fe418df5781395db6 in tip.

We will use this later in the series to eliminate the need for a function
call.

[ Steven Rostedt: added task_is_current function ]

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index f342f61..f743779 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1287,10 +1287,8 @@ struct task_struct {
 	int lock_depth;		/* BKL lock depth */
 
 #ifdef CONFIG_SMP
-#ifdef __ARCH_WANT_UNLOCKED_CTXSW
 	int oncpu;
 #endif
-#endif
 
 	int prio, static_prio, normal_prio;
 	unsigned int rt_priority;
@@ -2084,6 +2082,13 @@ extern void set_curr_task(int cpu, struct task_struct *p);
 void yield(void);
 void __yield(void);
 
+#ifdef CONFIG_SMP
+static inline int task_is_current(struct task_struct *task)
+{
+	return task->oncpu;
+}
+#endif
+
 /*
  * The default (Linux) execution domain.
  */
@@ -2742,8 +2747,6 @@ static inline unsigned long rlimit_max(unsigned int limit)
 	return task_rlimit_max(current, limit);
 }
 
-extern int task_is_current(struct task_struct *task);
-
 #endif /* __KERNEL__ */
 
 #endif
diff --git a/kernel/sched.c b/kernel/sched.c
index c486ea2..9d1c4cf 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -697,10 +697,12 @@ inline void update_rq_clock(struct rq *rq)
 	rq->clock = sched_clock_cpu(cpu_of(rq));
 }
 
+#ifndef CONFIG_SMP
 int task_is_current(struct task_struct *task)
 {
 	return task_rq(task)->curr == task;
 }
+#endif
 
 /*
  * Tunables that become constants when CONFIG_SCHED_DEBUG is off:
@@ -918,18 +920,39 @@ static inline int task_current(struct rq *rq, struct task_struct *p)
 	return rq->curr == p;
 }
 
-#ifndef __ARCH_WANT_UNLOCKED_CTXSW
 static inline int task_running(struct rq *rq, struct task_struct *p)
 {
+#ifdef CONFIG_SMP
+	return p->oncpu;
+#else
 	return task_current(rq, p);
+#endif
 }
 
+#ifndef __ARCH_WANT_UNLOCKED_CTXSW
 static inline void prepare_lock_switch(struct rq *rq, struct task_struct *next)
 {
+#ifdef CONFIG_SMP
+	/*
+	 * We can optimise this out completely for !SMP, because the
+	 * SMP rebalancing from interrupt is the only thing that cares
+	 * here.
+	 */
+	next->oncpu = 1;
+#endif
 }
 
 static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev)
 {
+#ifdef CONFIG_SMP
+	/*
+	 * After ->oncpu is cleared, the task can be moved to a different CPU.
+	 * We must ensure this doesn't happen until the switch is completely
+	 * finished.
+	 */
+	smp_wmb();
+	prev->oncpu = 0;
+#endif
 #ifdef CONFIG_DEBUG_SPINLOCK
 	/* this is a valid case when another task releases the spinlock */
 	rq->lock.owner = current;
@@ -945,14 +968,6 @@ static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev)
 }
 
 #else /* __ARCH_WANT_UNLOCKED_CTXSW */
-static inline int task_running(struct rq *rq, struct task_struct *p)
-{
-#ifdef CONFIG_SMP
-	return p->oncpu;
-#else
-	return task_current(rq, p);
-#endif
-}
 
 static inline void prepare_lock_switch(struct rq *rq, struct task_struct *next)
 {
@@ -2751,7 +2766,7 @@ void sched_fork(struct task_struct *p, int clone_flags)
 	if (likely(sched_info_on()))
 		memset(&p->sched_info, 0, sizeof(p->sched_info));
 #endif
-#if defined(CONFIG_SMP) && defined(__ARCH_WANT_UNLOCKED_CTXSW)
+#if defined(CONFIG_SMP)
 	p->oncpu = 0;
 #endif
 #ifdef CONFIG_PREEMPT
@@ -7380,7 +7395,7 @@ void __cpuinit init_idle(struct task_struct *idle, int cpu)
 	__set_task_cpu(idle, cpu);
 
 	rq->curr = rq->idle = idle;
-#if defined(CONFIG_SMP) && defined(__ARCH_WANT_UNLOCKED_CTXSW)
+#if defined(CONFIG_SMP)
 	idle->oncpu = 1;
 #endif
 	raw_spin_unlock_irqrestore(&rq->lock, flags);
-- 
1.7.1.1