On Tue, Jun 03, 2014 at 07:24:38PM +0800, Lai Jiangshan wrote:
> Hi, Jason
>
> Could you test again after the following command has done.
> (if Peter hasn't asked you test with this command before nor he doesn't stop
> you now)
>
> echo NO_TTWU_QUEUE > /sys/kernel/debug/sched_features
>
> Thanks a lot.
>
> Hi, Peter,
>
> I found something strange by review (just by review, no test yet)
>
> __migrate_task()
> {
> ...
> /*
> * If we're not on a rq, the next wake-up will ensure we're
> * placed properly.
> */
> if (p->on_rq) {
> dequeue_task(rq_src, p, 0);
> set_task_cpu(p, dest_cpu);
> enqueue_task(rq_dest, p, 0);
> check_preempt_curr(rq_dest, p, 0);
> }
> ...
> }
>
> The comment is incorrect if TTWU_QUEUE is enabled.
> The task is waken-up even p->on_rq==0 in this case:
> p->wake_entry is added to the rq,
> p->state is TASK_WAKING
> p->on_rq is 0
>
> In this case __migrate_task() fails to migrate the task!!!.
>
> Go back to workqueue for higher level analysing.
>
> task1 cpu#4 task3
> workqueue_cpu_up_callback()
> wake_up_process(worker1)
> ttwu_queue_remote()
> #queue worker1 to cpu#4
> set_cpus_allowed_ptr()
> set worker's cpuallowed to
> cpumask_of(5)
> #stopper_task
> __migrate_task()
> finds p->on_rq is 0,
> do nothing return
> set_cpus_allowed_ptr() return 0
>
> In this case, the WARN_ON() in process_one_work() hit.
Hmm, yes I think you're right. A queued wakeup can miss an affinity
change like that.
Something like the below ought to cure that I suppose..
---
kernel/sched/core.c | 21 +++++++++++++++------
1 file changed, 15 insertions(+), 6 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 240aa83e73f5..0708ee21632f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1521,17 +1521,32 @@ static int ttwu_remote(struct task_struct *p, int
wake_flags)
}
#ifdef CONFIG_SMP
+static void ttwu_queue_remote(struct task_struct *p, int cpu)
+{
+ if (llist_add(&p->wake_entry, &cpu_rq(cpu)->wake_list))
+ smp_send_reschedule(cpu);
+}
+
static void sched_ttwu_pending(void)
{
struct rq *rq = this_rq();
struct llist_node *llist = llist_del_all(&rq->wake_list);
struct task_struct *p;
+ int cpu;
raw_spin_lock(&rq->lock);
while (llist) {
p = llist_entry(llist, struct task_struct, wake_entry);
llist = llist_next(llist);
+
+ if (unlikely(!cpumask_test_cpu(rq->cpu, tsk_cpus_allowed(p)))) {
+ cpu = select_fallback_rq(rq->cpu, p);
+ set_task_cpu(p, cpu);
+ ttwu_queue_remote(p, cpu);
+ continue;
+ }
+
ttwu_do_activate(rq, p, 0);
}
@@ -1579,12 +1594,6 @@ void scheduler_ipi(void)
irq_exit();
}
-static void ttwu_queue_remote(struct task_struct *p, int cpu)
-{
- if (llist_add(&p->wake_entry, &cpu_rq(cpu)->wake_list))
- smp_send_reschedule(cpu);
-}
-
bool cpus_share_cache(int this_cpu, int that_cpu)
{
return per_cpu(sd_llc_id, this_cpu) == per_cpu(sd_llc_id, that_cpu);
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