Re: 2.4.19pre10aa3

[Andrea Arcangeli <andrea@suse.de>]

On Thu, Jun 20, 2002 at 04:40:33PM +0200, Andrea Arcangeli wrote:
> however I noticed an smp bug in my changes, I was too aggressive
> removing the loop in task_rq_lock, not that such bug ever triggered yet
> but the rq may change under us while we take the lock if the task is
> getting migrated to another cpu.

just for reference, here it is the fix:

--- sched/kernel/sched.c.~1~	Thu Jun 20 16:42:41 2002
+++ sched/kernel/sched.c	Thu Jun 20 16:43:36 2002
@@ -133,19 +133,13 @@ static inline runqueue_t *task_rq_lock(t
 {
 	struct runqueue *rq;
 
-	/*
-	 * 2.4 cannot be made preemptive or it can trigger preemption bugs all
-	 * over the place (just check the networking per-cpu data), so it's
-	 * pointless to disable irq before reading the current runqueue address.
-	 */
+repeat_lock_task:
 	rq = task_rq(p);
 	spin_lock_irqsave(&rq->lock, *flags);
-	if (unlikely(rq != task_rq(p)))
-		/*
-		 * Bug just in case somebody made the 2.4 kernel non preemptive
-		 * as an experiment on a non production system.
-		 */
-		BUG();
+	if (unlikely(rq != task_rq(p))) {
+		spin_unlock_irqrestore(&rq->lock, *flags);
+		goto repeat_lock_task;
+	}
 	return rq;
 }
 

Andrea