linux-kernel - Re: call_rcu from trace

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Date:	Wed, 17 Jun 2015 11:05:33 +0200
From:	Daniel Wagner <daniel.wagner@...-carit.de>
To:	Alexei Starovoitov <ast@...mgrid.com>, <paulmck@...ux.vnet.ibm.com>
CC:	LKML <linux-kernel@...r.kernel.org>, <rostedt@...dmis.org>
Subject: Re: call_rcu from trace_preempt

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.
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