linux-kernel - Re: [PATCH] gpio: pca953x: Survive spurious interrupts

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Date:   Wed, 7 Oct 2020 16:10:11 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        kernel-team@...roid.com
Subject: Re: [PATCH] gpio: pca953x: Survive spurious interrupts

On Wed, Oct 7, 2020 at 3:09 PM Marc Zyngier <maz@...nel.org> wrote:
> On 2020-10-07 13:02, Andy Shevchenko wrote:
> > On Wed, Oct 7, 2020 at 12:49 PM Linus Walleij
> > <linus.walleij@...aro.org> wrote:
> >> On Mon, Oct 5, 2020 at 4:02 PM Marc Zyngier <maz@...nel.org> wrote:
> >>
> >> > The pca953x driver never checks the result of irq_find_mapping(),
> >> > which returns 0 when no mapping is found. When a spurious interrupt
> >> > is delivered (which can happen under obscure circumstances), the
> >> > kernel explodes as it still tries to handle the error code as
> >> > a real interrupt.
> >> >
> >> > Handle this particular case and warn on spurious interrupts.
> >> >
> >> > Signed-off-by: Marc Zyngier <maz@...nel.org>
> >
> > Wait, doesn't actually [1]  fix the reported issue?
>
> Not at all.
>
> > Marc, can you confirm this?
> >
> > [1]: e43c26e12dd4 ("gpio: pca953x: Fix uninitialized pending variable")
>
> Different bug, really. If an interrupt is *really* pending, and no
> mapping established yet, feeding the result of irq_find_mapping() to
> handle_nested_irq() will lead to a panic.

I don't understand. We have plenty of drivers doing exactly the way
without checking this returned code. What circumstances makes the
mapping be absent?

Shouldn't we rather change this:

        girq->handler = handle_simple_irq;
to this:
        girq->handler = handle_bad_irq;
?

> Recently seen on a Tegra system suffering from even more pathological
> bugs.


-- 
With Best Regards,
Andy Shevchenko