Re: [PATCH] irq: Remove unnecessary warning with affinity_hint

Seiichi Ikarashi
2015-04-08T07:33:19Z

Hi,

On 2015-04-08 15:28, Ingo Molnar wrote:
>
> * Seiichi Ikarashi <s.ikarashi@jp.fujitsu.com> wrote:
>
>> Hi,
>>
>> If you turn off a PCI device whose driver has set affinity_hint,
>> you will get warning message which does _not_ explain the reason
>> why it appeared from the user's point of view.
>>
>> # echo 0 > /sys/bus/pci/slots/65/power
>>
>> Apr 28 20:29:39 localhost kernel: ------------[ cut here ]------------
>> Apr 28 20:29:39 localhost kernel: WARNING: at kernel/irq/manage.c:1002 __free_irq+0x22d/0x250() (Tainted: P --------------- )
>> (snip)
>>
>> Users will misunderstand some problem has happened
>> even though he or she succeeded to turn off the device.
>> I suppose this warning was originally for a debug purpose
>> for driver developers and has incidentally been left.
>>
>> Just remove the warning is good and enough.
>>
>> Signed-off-by: Seiichi Ikarashi <s.ikarashi@jp.fujitsu.com>
>>
>> --- a/kernel/irq/manage.c
>> +++ b/kernel/irq/manage.c
>> @@ -1335,7 +1335,7 @@ static struct irqaction *__free_irq(unsi
>>
>> #ifdef CONFIG_SMP
>> /* make sure affinity_hint is cleaned up */
>> - if (WARN_ON_ONCE(desc->affinity_hint))
>> + if (desc->affinity_hint)
>> desc->affinity_hint = NULL;
>
> Well, drivers that are using irq_set_affinity_hint() are expected to
> call:
>
> irq_set_affinity_hint(irq, NULL);
>
> to clear the affinity mask, before releasing the irq. This warning
> flags drivers that forgot to do that and which might thus leak a
> dynamically allocated CPU mask (and/or other resources).

Calling irq_set_affinity_hint(irq, NULL) does not guarantee that
the driver does not forget to deallocate a dynamically allocated
CPU mask and/or other resources. But if calling it with NULL 2nd-arg
before releasing the irq is a virtual rule of using irq_set_affinity_hint()
interface, I understand it.

>
> Feel free to turn the warning message into a more informative WARN()
> that will blame the driver that triggered it, if the stack dump into
> the driver wasn't a clue enough ...

Still, I do not know leaving the warning message is effective to
prevent drivers from potentially leaking resource... considering
a kind of cost-effectivenss. Business users (not developers) hate
such kind of messages for developers.

Thanks,
Seiichi