Subject: Re: BUG: sleeping function called from ras_epow_interrupt context

From: Thomas Huth <[email-masked]>
Date: Thu, 16 Jul 2015 08:23:53 +0200

On 07/15/2015 09:58 PM, Nathan Fontenot wrote:
> On 07/15/2015 09:35 AM, Thomas Huth wrote:
>> On 07/14/2015 11:22 PM, Benjamin Herrenschmidt wrote:
>>> On Tue, 2015-07-14 at 20:43 +0200, Thomas Huth wrote:
>>>> Any suggestions how to fix this? Simply revert 587f83e8dd50d? Use
>>>> mdelay() instead of msleep() in rtas_busy_delay()? Something more
>>>> fancy?
>>>
>>> A proper fix would be more fancy, the get_sensor should happen in a
>>> kernel thread instead.
>>
>> I'm not very familiar with this stuff, but isn't the EPOW interrupt
>> something that is very time-critical? Moving parts of the handler into a
>> kernel thread then does not sound like a very good idea to me...
>>
>> Another question: Can it happen at all that this get-sensor call results
>> in a sleep condition? Looking at commit ID
>> 81b73dd92b97423b8f5324a59044da478c04f4c4 ("Fix might-sleep warning on
>> removing cpus"), which apparently fixed a similar issue for CPU
>> hot-plugging, indicates that at least some of the rtas calls are never
>> returning the busy code? In that case we could fix this by introducing a
>> similar rtas_get_sensor_fast() function? (or simply revert 587f83e8dd50d
>> which would be quite similar, I think)
>>
> 
> Looking at the PAPR, the get-sensor-state rtas call for the EPOW sensor
> is listed as a fast call and should not return a busy indication.

Great, good to know, thanks for looking that up! So IMHO we should
either introduce a rtas_get_sensor_fast() function or revert
587f83e8dd50d ... any preferences? Shall I come up with a patch?

> I'm curious as to why we're getting a busy return indication when
> making this call.

Looking at the code again, rtas_busy_delay() likely never slept ... it's
likely just the "might_sleep()" annotation in that function that causes
the BUG.

 Thomas