[RFC, PATCH 8/9] CPU Controller V2 - task_cpu(p) needs to be correct always

Srivatsa Vaddagiri
2006-09-28T17:33:32Z

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@in.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