Re: [BUG] TASK_DEAD task is able to be woken up in special condition

Peter Zijlstra
2012-01-25T10:10:39Z

On Wed, 2011-12-28 at 16:07 -0500, KOSAKI Motohiro wrote:
>
> CPU0 CPU1
> --------------------------------------------------------
> deactivate_task()
> task->state = TASK_UNINTERRUPTIBLE;
> activate_task()
> rq->nr_uninterruptible--;
>
> schedule()
> deactivate_task()
> rq->nr_uninterruptible++;
>
>

Hmm, I think you're right, when CPU0 does __sched_setscheduler() on the
task running on CPU1 and CPU1's @task is current.

I think only __sched_setscheduler() is really a problem, the other
activate/deactivate users not schedule or wakeup are __migrate_task()
and normalize_task().

__migrate_task() will only run on tasks that aren't actually running
anywhere so the above scenario can't happen, normalize_task() is never
used on normal systems (sysrq-n).

So I guess the below cures things and cleans up a bit.. no?

---
kernel/sched/core.c | 18 ++++++------------
1 files changed, 6 insertions(+), 12 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index df00cb0..e067df1 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -723,9 +723,6 @@ static void dequeue_task(struct rq *rq, struct task_struct *p, int flags)
p->sched_class->dequeue_task(rq, p, flags);
}

-/*
- * activate_task - move a task to the runqueue.
- */
void activate_task(struct rq *rq, struct task_struct *p, int flags)
{
if (task_contributes_to_load(p))
@@ -734,9 +731,6 @@ void activate_task(struct rq *rq, struct task_struct *p, int flags)
enqueue_task(rq, p, flags);
}

-/*
- * deactivate_task - remove a task from the runqueue.
- */
void deactivate_task(struct rq *rq, struct task_struct *p, int flags)
{
if (task_contributes_to_load(p))
@@ -4134,7 +4128,7 @@ static int __sched_setscheduler(struct task_struct *p, int policy,
on_rq = p->on_rq;
running = task_current(rq, p);
if (on_rq)
- deactivate_task(rq, p, 0);
+ dequeue_task(rq, p, 0);
if (running)
p->sched_class->put_prev_task(rq, p);

@@ -4147,7 +4141,7 @@ static int __sched_setscheduler(struct task_struct *p, int policy,
if (running)
p->sched_class->set_curr_task(rq);
if (on_rq)
- activate_task(rq, p, 0);
+ enqueue_task(rq, p, 0);

check_class_changed(rq, p, prev_class, oldprio);
task_rq_unlock(rq, p, &flags);
@@ -4998,9 +4992,9 @@ static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
* placed properly.
*/
if (p->on_rq) {
- deactivate_task(rq_src, p, 0);
+ dequeue_task(rq_src, p, 0);
set_task_cpu(p, dest_cpu);
- activate_task(rq_dest, p, 0);
+ enqueue_task(rq_dest, p, 0);
check_preempt_curr(rq_dest, p, 0);
}
done:
@@ -7032,10 +7026,10 @@ static void normalize_task(struct rq *rq, struct task_struct *p)

on_rq = p->on_rq;
if (on_rq)
- deactivate_task(rq, p, 0);
+ dequeue_task(rq, p, 0);
__setscheduler(rq, p, SCHED_NORMAL, 0);
if (on_rq) {
- activate_task(rq, p, 0);
+ enqueue_task(rq, p, 0);
resched_task(rq->curr);
}