linux-kernel - Re: [RFC PATCH 2/2] arm64: support HAVE_IRQ_EXIT_ON_IRQ

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Date:   Thu, 7 Jul 2022 22:55:45 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Qi Zheng <zhengqi.arch@...edance.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 2/2] arm64: support HAVE_IRQ_EXIT_ON_IRQ_STACK

On Thu, Jul 7, 2022 at 5:00 PM Qi Zheng <zhengqi.arch@...edance.com> wrote:
> On 2022/7/7 22:41, Arnd Bergmann wrote:
> > On Thu, Jul 7, 2022 at 3:38 PM Qi Zheng <zhengqi.arch@...edance.com> wrote:
> >> On 2022/7/7 20:49, Arnd Bergmann wrote:
> >
> > -asmlinkage void noinstr el1h_64_fiq_handler(struct pt_regs *regs)
> > +asmlinkage void noinstr el1h_64_irq_handler(struct pt_regs *regs)
> > +{
> > +       if (on_thread_stack())
> > +               call_on_irq_stack(regs, el1_irq);
>
> IMO, this can't work. Because el1_interrupt() will invoke
> arm64_preempt_schedule_irq(), which will cause scheduling on the
> IRQ stack.

Ah, too bad. I spent some more time looking for a simpler approach,
but couldn't find one I'm happy with. One idea might be to have
callback functions for each combinations of irq/fiq with irq/pnmi
to avoid the nested callback pointers. Not sure if that helps.

       Arnd