[PATCH] arm: use cpu_online_mask when using forced irq_set_affinity

Russell King - ARM Linux linux at arm.linux.org.uk
Thu Aug 28 03:16:32 PDT 2014

On Thu, Aug 28, 2014 at 11:12:15AM +0100, Sudeep Holla wrote:
> On 28/08/14 10:32, Thomas Gleixner wrote:
>> On Tue, 26 Aug 2014, Sudeep Holla wrote:
>>>>> Can provide your thoughts on how to solve this issue ?
>>>> ffde1de64012 is not about offlining a cpu, it's about onlining where
>>>> we need to make sure that we assign the affinity to a not yet online
>>>> marked cpu.
>>>>> Is it expected from all the irqchip implementation to use force flag in
>>>>> irq_set_affinity to ignore cpu_online_mask similar to GIC ?
>>>> No, it's only relevant for the cases where we need to route irqs to
>>>> not yet online cpus.
>>> Ok. IIUC Russell's main concern was if irqchip implementation uses force
>>> flag differently, then we can't change the core code to false. Also
>>> x86 core code also uses forced irq_set_affinity in arch/x86/kernel/irq.c
>> Which is pointless as none of the x86 irq chip implementations
>> actually honours the force argument.
>> In fact until the point where I implemented it in the GIC driver,
>> nothing ever used that argument. So the GIC conversion actually added
>> semantics to the argument. Any driver which will make use of it, has
>> to follow that now. I'll add documentation to the core code for it ...
> Thanks Thomas for confirming.
> Hi Russell,
> Can I post the patch changing force to false in irq_set_affinity call
> to fix the issue and cc stable ? It's broken in stable kernels(v3.10 and
> v3.14)

I think it's up to Thomas to suggest what the correct solution is to
the problem he introduced, and it's not clear from Thomas' email you
quote above what he thinks would be the right solution.  It sounds
like passing false there would be the right thing, but really it needs
a clear and unambiguous statement from Thomas.

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