[PATCH -rt] Add schedule_work_prio() and queue_work_prio().

["Leon Woestenberg" <leon.woestenberg@gmail.com>]

Against 2.6.25.8-rt7, only compile tested.

Adds schedule_work_prio() and queue_work_prio() so that work can be
scheduled with a different priority than the caller.

Under PREEMPT RT, schedule_work() and therefore queue_work() makes
the work inherit the caller's priority.

If a real-time thread, such as an interrupt handler, defers work it
may want the deferred work to be of lower priority so it does not
race with succeeding interrupt handling.

Signed-off-by: Leon Woestenberg <leon@sidebranch.com>

Index: linux-2.6.25.8/kernel/workqueue.c
===================================================================
--- linux-2.6.25.8.orig/kernel/workqueue.c	2008-06-28 16:52:40.000000000 +0200
+++ linux-2.6.25.8/kernel/workqueue.c	2008-06-28 18:29:19.000000000 +0200
@@ -162,9 +162,10 @@
 }

 /**
- * queue_work - queue work on a workqueue
+ * queue_work_prio - queue work on a workqueue and set work priority
  * @wq: workqueue to use
  * @work: work to queue
+ * @prio: priority of work
  *
  * Returns 0 if @work was already on a queue, non-zero otherwise.
  *
@@ -173,7 +174,7 @@
  *
  * Especially no such guarantee on PREEMPT_RT.
  */
-int queue_work(struct workqueue_struct *wq, struct work_struct *work)
+int queue_work_prio(struct workqueue_struct *wq, struct work_struct
*work, int prio)
 {
 	int ret = 0, cpu = raw_smp_processor_id();

@@ -184,6 +185,25 @@
 	}
 	return ret;
 }
+EXPORT_SYMBOL_GPL(queue_work_prio);
+
+/**
+ * queue_work - queue work on a workqueue. work inherits caller's prio.
+ * @wq: workqueue to use
+ * @work: work to queue
+ *
+ * Returns 0 if @work was already on a queue, non-zero otherwise.
+ *
+ * We queue the work to the CPU it was submitted, but there is no
+ * guarantee that it will be processed by that CPU.
+ *
+ * Especially no such guarantee on PREEMPT_RT.
+ */
+int queue_work(struct workqueue_struct *wq, struct work_struct *work)
+{
+  return queue_work(struct workqueue_struct *wq, struct work_struct *work,
+    current->normal_prio);
+}
 EXPORT_SYMBOL_GPL(queue_work);

 static void delayed_work_timer_fn(unsigned long __data)
@@ -626,7 +646,8 @@
  * schedule_work - put work task in global workqueue
  * @work: job to be done
  *
- * This puts a job in the kernel-global workqueue.
+ * This puts a job in the kernel-global workqueue. The job inherits the
+ * caller's priority.
  */
 int schedule_work(struct work_struct *work)
 {
@@ -635,6 +656,19 @@
 EXPORT_SYMBOL(schedule_work);

 /**
+ * schedule_work_prio - put work task in global workqueue, set work prio
+ * @work: job to be done
+ *
+ * This puts a job in the kernel-global workqueue. The job gets the specified
+ * priority.
+ */
+int schedule_work_prio(struct work_struct *work, int prio)
+{
+	return queue_work_prio(keventd_wq, work, prio);
+}
+EXPORT_SYMBOL(schedule_work_prio);
+
+/**
  * schedule_delayed_work - put work task in global workqueue after delay
  * @dwork: job to be done
  * @delay: number of jiffies to wait or 0 for immediate execution

-- 
Leon