Messages in this thread Patch in this message | | | Date | Tue, 3 Jun 2014 16:16:59 +0200 | From | Peter Zijlstra <> | Subject | Re: workqueue: WARN at at kernel/workqueue.c:2176 |
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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);[unhandled content-type:application/pgp-signature] | |