Messages in this thread |  | | Subject | Re: Oops on Power8 (was Re: [PATCH v2 1/7] workqueue: make workqueue available early during boot) | From | Balbir Singh <> | Date | Sat, 15 Oct 2016 12:25:50 +1100 |
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On 15/10/16 02:07, Tejun Heo wrote: > Hello, Michael. > > On Tue, Oct 11, 2016 at 10:22:13PM +1100, Michael Ellerman wrote: >> The oops happens because we're in enqueue_task_fair() and p->se->cfs_rq >> is NULL. >> >> The cfs_rq is NULL because we did set_task_rq(p, 2048), where 2048 is >> NR_CPUS. That causes us to index past the end of the tg->cfs_rq array in >> set_task_rq() and happen to get NULL. >> >> We never should have done set_task_rq(p, 2048), because 2048 is >= >> nr_cpu_ids, which means it's not a valid CPU number, and set_task_rq() >> doesn't cope with that. > > Hmm... it doesn't reproduce it here and can't see how the commit would > affect this given that it doesn't really change when the kworker > kthreads are being created. > >> Presumably we shouldn't be ending up with tsk_cpus_allowed() being >> empty, but I haven't had time to track down why that's happening. >
I think the basic analysis shows the change to creation of unbounded workqueues from the unbound_hash, but those have a pool cpumask empty.
> Can you please add WARN_ON_ONCE(!tsk_nr_cpus_allowed(p)) to > select_task_rq() and post what that says? > > Thanks. >
Balbir Singh.
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