Re: [PATCH] gpio: pca953x: Survive spurious interrupts

[Andy Shevchenko <andy.shevchenko@xxxxxxxxx>]

On Wed, Oct 7, 2020 at 3:09 PM Marc Zyngier <maz@xxxxxxxxxx> wrote:
> On 2020-10-07 13:02, Andy Shevchenko wrote:
> > On Wed, Oct 7, 2020 at 12:49 PM Linus Walleij
> > <linus.walleij@xxxxxxxxxx> wrote:
> >> On Mon, Oct 5, 2020 at 4:02 PM Marc Zyngier <maz@xxxxxxxxxx> 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@xxxxxxxxxx>
> >
> > 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