[patch] sched: add cond_resched_softirq()

[Ingo Molnar]

the attached patch comes after preempt-lock-need-resched.patch.

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.)

	Ingo

the attached patch comes after preempt-lock-need-resched.patch.

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@xxxxxxx>

--- linux/include/linux/sched.h.orig	
+++ linux/include/linux/sched.h	
@@ -955,9 +955,12 @@ 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
--- linux/kernel/sched.c.orig	
+++ linux/kernel/sched.c	
@@ -3589,6 +3589,22 @@ 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.
  *