sched: Always provide p->on_cpu

Always provide p->on_cpu so that we can determine if its on a cpu
without having to lock the rq.

Reviewed-by: Frank Rowand <frank.rowand@am.sony.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20110405152728.785452014@chello.nl
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 29 insertions, 17 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index a187c3fe027b..cd2593e1a3ec 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -838,18 +838,39 @@ 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->on_cpu;
+#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->on_cpu = 1;
+#endif
 }
 
 static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev)
 {
+#ifdef CONFIG_SMP
+        /*
+         * After ->on_cpu 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->on_cpu = 0;
+#endif
 #ifdef CONFIG_DEBUG_SPINLOCK
         /* this is a valid case when another task releases the spinlock */
         rq->lock.owner = current;
@@ -865,15 +886,6 @@ 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)
 {
 #ifdef CONFIG_SMP
@@ -882,7 +894,7 @@ static inline void prepare_lock_switch(struct rq *rq, struct task_struct *next)
          * SMP rebalancing from interrupt is the only thing that cares
          * here.
          */
-        next->oncpu = 1;
+        next->on_cpu = 1;
 #endif
 #ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
         raw_spin_unlock_irq(&rq->lock);
@@ -895,12 +907,12 @@ 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.
+         * After ->on_cpu 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;
+        prev->on_cpu = 0;
 #endif
 #ifndef __ARCH_WANT_INTERRUPTS_ON_CTXSW
         local_irq_enable();
@@ -2686,8 +2698,8 @@ 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)
-        p->oncpu = 0;
+#if defined(CONFIG_SMP)
+        p->on_cpu = 0;
 #endif
 #ifdef CONFIG_PREEMPT
         /* Want to start with kernel preemption disabled. */
@@ -5776,8 +5788,8 @@ void __cpuinit init_idle(struct task_struct *idle, int cpu)
         rcu_read_unlock();
 
         rq->curr = rq->idle = idle;
-#if defined(CONFIG_SMP) && defined(__ARCH_WANT_UNLOCKED_CTXSW)
-        idle->oncpu = 1;
+#if defined(CONFIG_SMP)
+        idle->on_cpu = 1;
 #endif
         raw_spin_unlock_irqrestore(&rq->lock, flags);