linux-kernel - [RFC, PATCH 8/9] CPU Controller V2 - task

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Message-ID: <20060928173320.GI8746@in.ibm.com>
Date:	Thu, 28 Sep 2006 23:03:20 +0530
From:	Srivatsa Vaddagiri <vatsa@...ibm.com>
To:	Ingo Molnar <mingo@...e.hu>, Nick Piggin <nickpiggin@...oo.com.au>
Cc:	linux-kernel@...r.kernel.org, Kirill Korotaev <dev@...nvz.org>,
	Mike Galbraith <efault@....de>,
	Balbir Singh <balbir@...ibm.com>, sekharan@...ibm.com,
	Andrew Morton <akpm@...l.org>, nagar@...son.ibm.com,
	matthltc@...ibm.com, dipankar@...ibm.com,
	ckrm-tech@...ts.sourceforge.net
Subject: [RFC, PATCH 8/9] CPU Controller V2 - task_cpu(p) needs to be correct always

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@...ibm.com>

---

 linux-2.6.18-root/kernel/sched.c |   10 ++++++++--
 1 files changed, 8 insertions(+), 2 deletions(-)

diff -puN kernel/sched.c~cpu_ctlr_setcpu kernel/sched.c
--- linux-2.6.18/kernel/sched.c~cpu_ctlr_setcpu	2006-09-28 16:40:37.844287616 +0530
+++ linux-2.6.18-root/kernel/sched.c	2006-09-28 17:23:14.896556584 +0530
@@ -5230,6 +5230,7 @@ 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;
@@ -5245,8 +5246,8 @@ 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
@@ -5256,6 +5257,11 @@ static int __migrate_task(struct task_st
 		p->timestamp = p->timestamp - rq_src->timestamp_last_tick
 				+ rq_dest->timestamp_last_tick;
 		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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