[PATCH] preempt cleanup

This is another generic fallout from the voluntary-preempt patchset: a
cleanup of the cond_resched() infrastructure, in preparation of the latency
reduction patches.  The changes:

 - uninline cond_resched() - this makes the footprint smaller,
   especially once the number of cond_resched() points increase.

 - add a 'was rescheduled' return value to cond_resched. This makes it
   symmetric to cond_resched_lock() and later latency reduction patches
   rely on the ability to tell whether there was any preemption.

 - make cond_resched() more robust by using the same mechanism as
   preempt_kernel(): by using PREEMPT_ACTIVE. This preserves the task's
   state - e.g. if the task is in TASK_ZOMBIE but gets preempted via
   cond_resched() just prior scheduling off then this approach preserves
   TASK_ZOMBIE.

 - the patch also adds need_lockbreak() which critical sections can use 
   to detect lock-break requests.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 17 insertions, 6 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 1a05ab700f2330..a55af06f9976b1 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3433,13 +3433,25 @@ asmlinkage long sys_sched_yield(void)
 	return 0;
 }
 
-void __sched __cond_resched(void)
+static inline void __cond_resched(void)
 {
-	set_current_state(TASK_RUNNING);
-	schedule();
+	do {
+		preempt_count() += PREEMPT_ACTIVE;
+		schedule();
+		preempt_count() -= PREEMPT_ACTIVE;
+	} while (need_resched());
+}
+
+int __sched cond_resched(void)
+{
+	if (need_resched()) {
+		__cond_resched();
+		return 1;
+	}
+	return 0;
 }
 
-EXPORT_SYMBOL(__cond_resched);
+EXPORT_SYMBOL(cond_resched);
 
 /*
  * cond_resched_lock() - if a reschedule is pending, drop the given lock,
@@ -3462,8 +3474,7 @@ int cond_resched_lock(spinlock_t * lock)
 	if (need_resched()) {
 		_raw_spin_unlock(lock);
 		preempt_enable_no_resched();
-		set_current_state(TASK_RUNNING);
-		schedule();
+		__cond_resched();
 		spin_lock(lock);
 		return 1;
 	}