[PATCH] sync wakeup on UP

This fixes the scheduler's sync-wakeup code to be consistent on UP as
well.

Right now there's a behavioral difference between an UP kernel and an
SMP kernel running on a UP box: sync wakeups (which are only activated
on SMP) can cause a wakeup of a higher prio task, without preemption.
On UP kernels this does not happen.  This difference in wakeup behavior
is bad.

This patch activates sync wakeups on UP as well - in the cases sync
wakeups are done the waker knows that it will schedule away soon, so
this 'delay preemption' decision is correct on UP as well.

include/linux/wait.h

@@ -111,15 +111,12 @@ extern void FASTCALL(__wake_up_sync(wait_queue_head_t *q, unsigned int mode, int
 #define wake_up(x)			__wake_up((x),TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, 1)
 #define wake_up_nr(x, nr)		__wake_up((x),TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, nr)
 #define wake_up_all(x)			__wake_up((x),TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, 0)
+#define wake_up_all_sync(x)			__wake_up_sync((x),TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, 0)
 #define wake_up_interruptible(x)	__wake_up((x),TASK_INTERRUPTIBLE, 1)
 #define wake_up_interruptible_nr(x, nr)	__wake_up((x),TASK_INTERRUPTIBLE, nr)
 #define wake_up_interruptible_all(x)	__wake_up((x),TASK_INTERRUPTIBLE, 0)
 #define	wake_up_locked(x)		__wake_up_locked((x), TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE)
-#ifdef CONFIG_SMP
 #define wake_up_interruptible_sync(x)   __wake_up_sync((x),TASK_INTERRUPTIBLE, 1)
-#else
-#define wake_up_interruptible_sync(x)   __wake_up((x),TASK_INTERRUPTIBLE, 1)
-#endif
 
 #define __wait_event(wq, condition) 					\
 do {									\

kernel/sched.c

@@ -1414,8 +1414,6 @@ void __wake_up_locked(wait_queue_head_t *q, unsigned int mode)
 	__wake_up_common(q, mode, 1, 0);
 }
 
-#ifdef CONFIG_SMP
-
 /**
  * __wake_up - sync- wake up threads blocked on a waitqueue.
  * @q: the waitqueue
@@ -1426,6 +1424,8 @@ void __wake_up_locked(wait_queue_head_t *q, unsigned int mode)
  * away soon, so while the target thread will be woken up, it will not
  * be migrated to another CPU - ie. the two threads are 'synchronized'
  * with each other. This can prevent needless bouncing between CPUs.
+ *
+ * On UP it can prevent extra preemption.
  */
 void __wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr_exclusive)
 {
@@ -1442,8 +1442,6 @@ void __wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr_exclusive)
 	spin_unlock_irqrestore(&q->lock, flags);
 }
 
-#endif
-
 void complete(struct completion *x)
 {
 	unsigned long flags;