[PATCH] sched: add cond_resched_softirq()

It adds cond_resched_softirq() which can be used by _process context_
softirqs-disabled codepaths to preempt if necessary.  The function will
enable softirqs before scheduling.  (Later patches will use this
primitive.)
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/sched.h

@@ -1069,9 +1069,12 @@ static inline int need_resched(void)
  * cond_resched() and cond_resched_lock(): latency reduction via
  * explicit rescheduling in places that are safe. The return
  * value indicates whether a reschedule was done in fact.
+ * cond_resched_lock() will drop the spinlock before scheduling,
+ * cond_resched_softirq() will enable bhs before scheduling.
  */
 extern int cond_resched(void);
 extern int cond_resched_lock(spinlock_t * lock);
+extern int cond_resched_softirq(void);
 
 /*
  * Does a critical section need to be broken due to another

kernel/sched.c

@@ -3483,6 +3483,22 @@ int cond_resched_lock(spinlock_t * lock)
 
 EXPORT_SYMBOL(cond_resched_lock);
 
+int __sched cond_resched_softirq(void)
+{
+	BUG_ON(!in_softirq());
+
+	if (need_resched()) {
+		__local_bh_enable();
+		__cond_resched();
+		local_bh_disable();
+		return 1;
+	}
+	return 0;
+}
+
+EXPORT_SYMBOL(cond_resched_softirq);
+
+
 /**
  * yield - yield the current processor to other threads.
  *