[Devel] [PATCH 8/9] task_cpu(p) needs to be correct always

[Srivatsa Vaddagiri]

We rely very much on task_cpu(p) to be correct at all times, so that we can
correctly find the task_grp_rq from which the task has to be removed or added
to.

There is however one place in the scheduler where this assumption of
task_cpu(p) being correct is broken. This patch fixes that piece of code.

(Thanks to Balbir Singh for pointing this out to me)

Signed-off-by : Srivatsa Vaddagiri <vatsa at in.ibm.com>

---

---

 1 file changed, 8 insertions(+), 2 deletions(-)


---


diff -puN kernel/sched.c~task_cpu kernel/sched.c
--- linux-2.6.20/kernel/sched.c~task_cpu	2007-04-12 09:10:39.000000000 +0530
+++ linux-2.6.20-vatsa/kernel/sched.c	2007-04-12 11:07:14.000000000 +0530
@@ -5400,6 +5400,7 @@ static int __migrate_task(struct task_st
 {
 	struct rq *rq_dest, *rq_src;
 	int ret = 0;
+	struct prio_array *array;
 
 	if (unlikely(cpu_is_offline(dest_cpu)))
 		return ret;
@@ -5415,8 +5416,8 @@ static int __migrate_task(struct task_st
 	if (!cpu_isset(dest_cpu, p->cpus_allowed))
 		goto out;
 
-	set_task_cpu(p, dest_cpu);
-	if (p->array) {
+	array = p->array;
+	if (array) {
 		/*
 		 * Sync timestamp with rq_dest's before activating.
 		 * The same thing could be achieved by doing this step
@@ -5426,6 +5427,11 @@ static int __migrate_task(struct task_st
 		p->timestamp = p->timestamp - rq_src->most_recent_timestamp
 				+ rq_dest->most_recent_timestamp;
 		deactivate_task(p, rq_src);
+	}
+
+	set_task_cpu(p, dest_cpu);
+
+	if (array) {
 		__activate_task(p, rq_dest);
 		if (TASK_PREEMPTS_CURR(p, rq_dest))
 			resched_task(rq_dest->curr);
_
-- 
Regards,
vatsa
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