[PATCH] irq: Remove unnecessary warning with affinity_hint

[PATCH] irq: Remove unnecessary warning with affinity_hint

[Seiichi Ikarashi]

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 is appeared from the users' 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;
 #endif
 

[PATCH] irq: Remove unnecessary warning with affinity_hint

[Seiichi Ikarashi]

Hi Thomas,

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;
 #endif
 

[PATCH] irq: Remove unnecessary warning with affinity_hint

[Seiichi Ikarashi]

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;
 #endif
 

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

[Ingo Molnar]

* 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).

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 ...

Thanks,

	Ingo

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

[Seiichi Ikarashi]

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

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

[Ingo Molnar]

* Seiichi Ikarashi <s.ikarashi@jp.fujitsu.com> wrote:

> 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. [...]

I said 'might leak', not 'guaranteed to leak'.

Calling irq_set_affinity_hint(irq, NULL) is the way this kernel API is 
specified to be used. Forgetting to do it is a kernel driver bug and 
triggers a warning message from the kernel's IRQ subsystem.

> [...] 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.

it's a warning message pointing out a kernel bug: that 
irq_set_affinity_hint(irq, NULL) was not called properly.

Messages pointing out kernel bugs should be fixed, not hidden.

Thanks,

	Ingo

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

[Seiichi Ikarashi]

On 2015-04-08 16:39, Ingo Molnar wrote:
> 
> * Seiichi Ikarashi <s.ikarashi@jp.fujitsu.com> wrote:
> 
>> 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. [...]
> 
> I said 'might leak', not 'guaranteed to leak'.

Yes, I know.
I wrote it because I was not sure about the primary purpose of
showing the warning message.

> 
> Calling irq_set_affinity_hint(irq, NULL) is the way this kernel API is 
> specified to be used. Forgetting to do it is a kernel driver bug and 
> triggers a warning message from the kernel's IRQ subsystem.
> 
>> [...] 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.
> 
> it's a warning message pointing out a kernel bug: that 
> irq_set_affinity_hint(irq, NULL) was not called properly.
> 
> Messages pointing out kernel bugs should be fixed, not hidden.

OK, the conclusion is that a kernel bug on using irq_set_affinity_hint().

Thanks, Ingo.

Seiichi