linux-kernel - Re: [PATCH v3 2/3] genirq: Always limit the affinity to online CPUs

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Message-ID: <39f69dfe-32e5-4cb3-118b-5c02b28cbcff@samsung.com>
Date:   Thu, 14 Apr 2022 13:08:53 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        'Linux Samsung SOC' <linux-samsung-soc@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        John Garry <john.garry@...wei.com>,
        Xiongfeng Wang <wangxiongfeng2@...wei.com>,
        David Decotigny <ddecotig@...gle.com>,
        Krzysztof Kozlowski <krzk@...nel.org>
Subject: Re: [PATCH v3 2/3] genirq: Always limit the affinity to online CPUs

Hi Marc,

On 14.04.2022 12:35, Marc Zyngier wrote:
> On Thu, 14 Apr 2022 10:09:31 +0100,
> Marek Szyprowski <m.szyprowski@...sung.com> wrote:
>> On 13.04.2022 19:26, Marc Zyngier wrote:
>>> On Wed, 13 Apr 2022 15:59:21 +0100,
>>> Marek Szyprowski <m.szyprowski@...sung.com> wrote:
>>>> On 05.04.2022 20:50, Marc Zyngier wrote:
>>>>> When booting with maxcpus=<small number> (or even loading a driver
>>>>> while most CPUs are offline), it is pretty easy to observe managed
>>>>> affinities containing a mix of online and offline CPUs being passed
>>>>> to the irqchip driver.
>>>>>
>>>>> This means that the irqchip cannot trust the affinity passed down
>>>>> from the core code, which is a bit annoying and requires (at least
>>>>> in theory) all drivers to implement some sort of affinity narrowing.
>>>>>
>>>>> In order to address this, always limit the cpumask to the set of
>>>>> online CPUs.
>>>>>
>>>>> Signed-off-by: Marc Zyngier <maz@...nel.org>
>>>> This patch landed in linux next-20220413 as commit 33de0aa4bae9
>>>> ("genirq: Always limit the affinity to online CPUs"). Unfortunately it
>>>> breaks booting of most ARM 32bit Samsung Exynos based boards.
>>>>
>>>> I don't see anything specific in the log, though. Booting just hangs at
>>>> some point. The only Samsung Exynos boards that boot properly are those
>>>> Exynos4412 based.
>>>>
>>>> I assume that this is related to the Multi Core Timer IRQ configuration
>>>> specific for that SoCs. Exynos4412 uses PPI interrupts, while all other
>>>> Exynos SoCs have separate IRQ lines for each CPU.
>>>>
>>>> Let me know how I can help debugging this issue.
>>> Thanks for the heads up. Can you pick the last working kernel, enable
>>> CONFIG_GENERIC_IRQ_DEBUGFS, and dump the /sys/kernel/debug/irq/irqs/
>>> entries for the timer IRQs?
>> Exynos4210, Trats board, next-20220411:
> Thanks for all of the debug, super helpful. The issue is that we don't
> handle the 'force' case, which a handful of drivers are using when
> bringing up CPUs (and doing so before the CPUs are marked online).
>
> Can you please give the below hack a go?

This patch fixed the issue. Thanks! Feel free to add my:

Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>

Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland