Re: call_rcu from trace_preempt

[Daniel Wagner <daniel.wagner@bmw-carit.de>]

On 06/17/2015 10:11 AM, Daniel Wagner wrote:
> On 06/16/2015 07:20 PM, Alexei Starovoitov wrote:
>> On 6/16/15 5:38 AM, Daniel Wagner wrote:
>>> static int free_thread(void *arg)
>>> +{
>>> +    unsigned long flags;
>>> +    struct htab_elem *l;
>>> +
>>> +    while (!kthread_should_stop()) {
>>> +        spin_lock_irqsave(&elem_freelist_lock, flags);
>>> +        while (!list_empty(&elem_freelist)) {
>>> +            l = list_entry(elem_freelist.next,
>>> +                struct htab_elem, list);
>>> +            list_del(&l->list);
>>> +            kfree(l);
>>
> Anyway, I changed to above kfree() to a kfree_rcu() and it explodes
> again. With the same stack trace we seen.

Correction. I did this without the is_rcu_watching() change. With that
patch applied it works fine again.

> Steven's suggestion deferring the work via irq_work results in the same
> stack trace. (Now I get cold feets, without the nice heat from the CPU
> busy looping...)

That one still not working. It also makes the system really really slow.
I guess I still do something completely wrong.