linux-kernel - Re: [PATCH] arm64: fix a migrating irq bug when hotplug cpu

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Message-ID: <55E3020C.8020303@linaro.org>
Date:	Sun, 30 Aug 2015 21:15:56 +0800
From:	Hanjun Guo <hanjun.guo@...aro.org>
To:	Marc Zyngier <marc.zyngier@....com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Yang Yingliang <yangyingliang@...wei.com>
CC:	linux-arm-kernel@...ts.infradead.org,
	Mark Rutland <mark.rutland@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Will Deacon <will.deacon@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: fix a migrating irq bug when hotplug cpu

On 08/30/2015 02:12 AM, Marc Zyngier wrote:
> On 2015-08-29 16:12, Jiang Liu wrote:
>> On 2015/8/29 21:00, Yang Yingliang wrote:
>>> From: Yang Yingliang <yangyingliang@...wei.com>
>>>
>>> When cpu is disabled, all irqs will be migratged to another cpu.
>>> In some cases, a new affinity is different, it needed to be coppied
>>> to irq's affinity. But if the type of irq is LPI, it's affinity will
>>> not be coppied because of irq_set_affinity's return value.
>>> So copy the affinity, when the return value is IRQ_SET_MASK_OK_DONE.
>> Hi Yingliang,
>>     If irq_set_affinity callback returns IRQ_SET_MASK_OK_DONE,
>> it means that irq_set_affinity has copied the new CPU mask to irq
>> affinity mask. It would be better to change irq_set_affinity for LPI
>> to follow this rule.
>
> The main issue here seems to be that we do not call irq_set_affinity, but
> that we directly call into the top-level irqchip method, which relies on
> the core code to do the copy (see irq_do_set_affinity). Too bad.
>
> It feels like the arm/arm64 code would probably be better consolidated into
> kernel/irq/migration.c, which already deals with some of this for x86
> and ia64. It would save us the duplication and will make sure we don't
> miss things next time we add a new return code, as irq_do_set_affinity
> would handle this properly.
>
> Thoughts?

I agree. In arch/arm64/kernel/irq.c the irq migrate code is the same
as ARM32, and it's duplicate. But this is a bugfix, can we fix it in
a simple way, and refactor the code later?

Thanks
Hanjun
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