sched: add in_atomic_preempt_off()

add in_atomic_preempt_off() - debugging helper that will
simplify schedule().
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/hardirq.h

@@ -78,6 +78,19 @@
 # define in_atomic()	((preempt_count() & ~PREEMPT_ACTIVE) != 0)
 #endif
 
+#ifdef CONFIG_PREEMPT
+# define PREEMPT_CHECK_OFFSET 1
+#else
+# define PREEMPT_CHECK_OFFSET 0
+#endif
+
+/*
+ * Check whether we were atomic before we did preempt_disable():
+ * (used by the scheduler)
+ */
+#define in_atomic_preempt_off() \
+		((preempt_count() & ~PREEMPT_ACTIVE) != PREEMPT_CHECK_OFFSET)
+
 #ifdef CONFIG_PREEMPT
 # define preemptible()	(preempt_count() == 0 && !irqs_disabled())
 # define IRQ_EXIT_OFFSET (HARDIRQ_OFFSET-1)