linux-kernel - Re: [PATCH 2/3] genirq/irqdomain: Re-check mapping after associate in irq_create

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Date:   Wed, 8 Jan 2020 16:07:35 +0100
From:   Alexander Sverdlin <alexander.sverdlin@...ia.com>
To:     Marc Zyngier <maz@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Grant Likely <grant.likely@...retlab.ca>
Cc:     Mark Brown <broonie@...nsource.wolfsonmicro.com>,
        Jon Hunter <jonathanh@...dia.com>,
        "Glavinic-Pecotic, Matija (EXT - DE/Ulm)" 
        <matija.glavinic-pecotic.ext@...ia.com>,
        "Adamski, Krzysztof (Nokia - PL/Wroclaw)" 
        <krzysztof.adamski@...ia.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH 2/3] genirq/irqdomain: Re-check mapping after associate in
 irq_create_mapping()

Hello Marc,

On 20/09/2019 17:52, Marc Zyngier wrote:
> On 12/09/2019 10:44, Sverdlin, Alexander (Nokia - DE/Ulm) wrote:
>> From: Alexander Sverdlin <alexander.sverdlin@...ia.com>
>>
>> If two irq_create_mapping() calls perform a mapping of the same hwirq on
>> two CPU cores in parallel they both will get 0 from irq_find_mapping(),
>> both will allocate unique virq using irq_domain_alloc_descs() and both
>> will finally irq_domain_associate() it. Giving different virq numbers
>> to their callers.
>>
>> In practice the first caller is usually an interrupt controller driver and
>> the seconds is some device requesting the interrupt providede by the above
>> interrupt controller.
> I disagree with this "In practice". An irqchip controller should *very
> rarely* call irq_create_mapping on its own. It usually indicates some
> level of brokenness, unless the mapped interrupt is exposed by the
> irqchip itself (the GIC maintenance interrupt, for example).
> 
>> In this case either the interrupt controller driver configures virq which
>> is not the one being "associated" with hwirq, or the "slave" device
>> requests the virq which is never being triggered.
> Why should the interrupt controller configure that interrupt? On any
> sane platform, the mapping should be created by the user of the
> interrupt, and not by the provider.
> 
> This doesn't mean we shouldn't fix the irqdomain races, but I tend to
> disagree with the analysis here.

would you have time to review v2 of this series?

-- 
Best regards,
Alexander Sverdlin.