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Date: Wed, 27 Jul 2016 17:23:05 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Heiko Carstens <heiko.carstens@de.ibm.com>
cc: Peter Zijlstra <peterz@infradead.org>, LKML <linux-kernel@vger.kernel.org>,
        Tejun Heo <tj@kernel.org>
Subject: Re: [bisected] "sched: Allow per-cpu kernel threads to run on online
 && !active" causes warning
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References: <20160727125412.GB3912@osiris>
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On Wed, 27 Jul 2016, Heiko Carstens wrote:
> [    3.162961] ([<0000000000176c30>] select_task_rq+0xc0/0x1a8)
> [    3.162963] ([<0000000000177d64>] try_to_wake_up+0x2e4/0x478)
> [    3.162968] ([<000000000015d46c>] create_worker+0x174/0x1c0)
> [    3.162971] ([<0000000000161a98>] alloc_unbound_pwq+0x360/0x438)

> For some unknown reason select_task_rq() gets called with a task that has
> nr_cpus_allowed == 0. Hence "cpu = cpumask_any(tsk_cpus_allowed(p));"
> within select_task_rq() will set cpu to nr_cpu_ids which in turn causes the
> warning later on.
> 
> It only happens with more than one node, otherwise it seems to work fine.
> 
> Any idea what could be wrong here?

create_worker()
    tsk = kthread_create_on_node();
    kthread_bind_mask(tsk, pool->attrs->cpumask);
        do_set_cpus_allowed(tsk, mask);
            set_cpus_allowed_common(tsk, mask);
                cpumask_copy(&tsk->cpus_allowed, mask);
                tsk->nr_cpus_allowed = cpumask_weight(mask);
    wake_up_process(task);

So this looks like pool->attrs->cpumask is simply empty.....

Thanks,

	tglx