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

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Message-ID: <b53dbf64-b824-89b0-dc00-b894cf9771a9@bytedance.com>
Date:   Fri, 8 Jul 2022 11:13:34 +0800
From:   Qi Zheng <zhengqi.arch@...edance.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     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 2022/7/8 04:55, Arnd Bergmann wrote:
> 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.

Maybe nested callback pointers are not always a wild beast. ;)
This method does not change much, and we can also conveniently stuff
all kinds of things in do_handler() that we want to run on the IRQ
stack in addition to the handler().

Thanks,
Qi

> 
>         Arnd

-- 
Thanks,
Qi