[PATCH 2.6.30] schedule_work() documentation improvements

[Bart Van Assche <bart.vanassche@gmail.com>]

Two important aspects of the schedule_work() function are not yet documented:
- that it is allowed to pass a struct work_struct * to this function that
  is already on the kernel-global workqueue;
- the meaning of its return value.
The patch below documents both aspects.

Signed-off-by: Bart Van Assche <bart.vanassche@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Ingo Molnar <mingo@elte.hu>

diff -uprN orig/linux-2.6.30/kernel/workqueue.c linux-2.6.30/kernel/workqueue.c
--- orig/linux-2.6.30/kernel/workqueue.c	2009-06-10 05:05:27.000000000 +0200
+++ linux-2.6.30/kernel/workqueue.c	2009-07-30 18:58:07.000000000 +0200
@@ -603,7 +603,11 @@ static struct workqueue_struct *keventd_
  * schedule_work - put work task in global workqueue
  * @work: job to be done
  *
- * This puts a job in the kernel-global workqueue.
+ * Returns zero if @work was already on the kernel-global workqueue and
+ * non-zero otherwise.
+ *
+ * This puts a job in the kernel-global workqueue if it was not already queued
+ * and leaves it in the same position on the kernel-global workqueue otherwise.
  */
 int schedule_work(struct work_struct *work)
 {