Preempt functions are common and go in scheduler.c

Signed-off-by: Con Kolivas <kernel@kolivas.org>

Index: linux-2.6.10-rc1-mm2-plugsched1/kernel/scheduler.c
===================================================================
--- linux-2.6.10-rc1-mm2-plugsched1.orig/kernel/scheduler.c	2004-10-29 21:45:10.306944867 +1000
+++ linux-2.6.10-rc1-mm2-plugsched1/kernel/scheduler.c	2004-10-29 21:46:33.969888143 +1000
@@ -63,6 +63,84 @@ void kick_process(task_t *p)
 }
 #endif
 
+#ifdef CONFIG_PREEMPT
+#ifdef CONFIG_DEBUG_PREEMPT
+
+void fastcall add_preempt_count(int val)
+{
+	/*
+	 * Underflow?
+	 */
+	BUG_ON(((int)preempt_count() < 0));
+	preempt_count() += val;
+	/*
+	 * Spinlock count overflowing soon?
+	 */
+	BUG_ON((preempt_count() & PREEMPT_MASK) >= PREEMPT_MASK-10);
+}
+EXPORT_SYMBOL(add_preempt_count);
+
+void fastcall sub_preempt_count(int val)
+{
+	/*
+	 * Underflow?
+	 */
+	BUG_ON(val > preempt_count());
+	/*
+	 * Is the spinlock portion underflowing?
+	 */
+	BUG_ON((val < PREEMPT_MASK) && !(preempt_count() & PREEMPT_MASK));
+	preempt_count() -= val;
+}
+EXPORT_SYMBOL(sub_preempt_count);
+
+#endif
+
+/*
+ * this is is the entry point to schedule() from in-kernel preemption
+ * off of preempt_enable.  Kernel preemptions off return from interrupt
+ * occur there and call schedule directly.
+ */
+asmlinkage void __sched preempt_schedule(void)
+{
+	struct thread_info *ti = current_thread_info();
+#ifdef CONFIG_PREEMPT_BKL
+	struct task_struct *task = current;
+	int saved_lock_depth;
+#endif
+	/*
+	 * If there is a non-zero preempt_count or interrupts are disabled,
+	 * we do not want to preempt the current task.  Just return..
+	 */
+	if (unlikely(ti->preempt_count || irqs_disabled()))
+		return;
+
+need_resched:
+	add_preempt_count(PREEMPT_ACTIVE);
+	/*
+	 * We keep the big kernel semaphore locked, but we
+	 * clear ->lock_depth so that schedule() doesnt
+	 * auto-release the semaphore:
+	 */
+#ifdef CONFIG_PREEMPT_BKL
+	saved_lock_depth = task->lock_depth;
+	task->lock_depth = -1;
+#endif
+	schedule();
+#ifdef CONFIG_PREEMPT_BKL
+	task->lock_depth = saved_lock_depth;
+#endif
+	sub_preempt_count(PREEMPT_ACTIVE);
+
+	/* we could miss a preemption opportunity between schedule and now */
+	barrier();
+	if (unlikely(test_thread_flag(TIF_NEED_RESCHED)))
+		goto need_resched;
+}
+
+EXPORT_SYMBOL(preempt_schedule);
+#endif /* CONFIG_PREEMPT */
+
 extern struct sched_drv ingo_sched_drv;
 static const struct sched_drv *scheduler = &ingo_sched_drv;