sched: make task->oncpu available in all configurations

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>

include/linux/sched.h

@@ -1220,9 +1220,7 @@ 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;
@@ -2586,7 +2584,12 @@ static inline void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
 
 #define TASK_STATE_TO_CHAR_STR "RMSDTtZX"
 
-extern int task_is_current(struct task_struct *task);
+#ifdef CONFIG_SMP
+static inline int task_is_current(struct task_struct *task)
+{
+	return task->oncpu;
+}
+#endif
 
 #endif /* __KERNEL__ */
 

kernel/sched.c

@@ -752,10 +752,12 @@ 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:
@@ -969,18 +971,39 @@ 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;
@@ -996,14 +1019,6 @@ 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)
 {
@@ -2759,7 +2774,7 @@ 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
@@ -7235,7 +7250,7 @@ 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
 	atomic_spin_unlock_irqrestore(&rq->lock, flags);