linux-kernel - Re: [PATCH v5 1/5] arm64: Add framework to turn IPI as NMI

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Date:   Tue, 20 Oct 2020 11:08:30 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Sumit Garg <sumit.garg@...aro.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Mark Rutland <mark.rutland@....com>,
        julien.thierry.kdev@...il.com,
        Douglas Anderson <dianders@...omium.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jason Wessel <jason.wessel@...driver.com>,
        Masayoshi Mizuma <msys.mizuma@...il.com>,
        ito-yuichi@...itsu.com, kgdb-bugreport@...ts.sourceforge.net,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 1/5] arm64: Add framework to turn IPI as NMI

On 2020-10-20 07:43, Sumit Garg wrote:
> On Mon, 19 Oct 2020 at 17:07, Marc Zyngier <maz@...nel.org> wrote:

[...]

>> > +{
>> > +     if (!ipi_desc)
>> > +             return;
>> > +
>> > +     if (is_nmi) {
>> > +             if (!prepare_percpu_nmi(ipi_id))
>> > +                     enable_percpu_nmi(ipi_id, IRQ_TYPE_NONE);
>> > +     } else {
>> > +             enable_percpu_irq(ipi_id, IRQ_TYPE_NONE);
>> 
>> I'm not keen on this. Normal IRQs can't reliably work, so why do you
>> even bother with this?
> 
> Yeah I agree but we need to support existing functionality for kgdb
> roundup and sysrq backtrace using normal IRQs as well.

When has this become a requirement? I don't really see the point in
implementing something that is known not to work.

         M.
-- 
Jazz is not dead. It just smells funny...