netdev - Re: [PATCH net] r8169: fix operation under forced interrupt threading

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Message-ID: <87y2jpe5by.fsf@nanos.tec.linutronix.de>
Date:   Thu, 29 Oct 2020 10:42:25 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Heiner Kallweit <hkallweit1@...il.com>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Serge Belyshev <belyshev@...ni.sinp.msu.ru>,
        David Miller <davem@...emloft.net>,
        Realtek linux nic maintainers <nic_swsd@...ltek.com>,
        "netdev\@vger.kernel.org" <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net] r8169: fix operation under forced interrupt threading

On Thu, Oct 29 2020 at 09:42, Heiner Kallweit wrote:
> On 29.10.2020 00:29, Jakub Kicinski wrote:
>> Other handles may take spin_locks, which will sleep on RT.
>> 
>> I guess we may need to switch away from the _irqoff() variant for
>> drivers with IRQF_SHARED after all :(
>> 
> Right. Unfortunately that's a large number of drivers,
> e.g. pci_request_irq() sets IRQF_SHARED in general.

IRQF_SHARED is not the problem. It only becomes a problem when the
interrupt is actually shared which is only the case with the legacy PCI
interrupt. MSI[X] is not affected at all.

> But at least for now there doesn't seem to be a better way to deal
> with the challenges imposed by forced threading and shared irqs.

We still can do the static key trick, though it's admittedly hacky.

Thanks,

        tglx