linux-kernel - Re: [PATCH 1/2] gpio: sim: dispose of irq mappings before destroying the irq

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Message-ID: <ZOS8CYJufrnPlWXz@smile.fi.intel.com>
Date:   Tue, 22 Aug 2023 16:45:45 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Kent Gibson <warthog618@...il.com>, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH 1/2] gpio: sim: dispose of irq mappings before destroying
 the irq_sim domain

On Tue, Aug 22, 2023 at 03:46:38PM +0300, Andy Shevchenko wrote:
> On Tue, Aug 22, 2023 at 02:38:28PM +0200, Bartosz Golaszewski wrote:
> > On Tue, Aug 22, 2023 at 2:24 PM Andy Shevchenko
> > <andriy.shevchenko@...ux.intel.com> wrote:
> > > On Tue, Aug 22, 2023 at 02:16:44PM +0200, Bartosz Golaszewski wrote:
> > > > On Tue, Aug 22, 2023 at 2:12 PM Andy Shevchenko
> > > > <andriy.shevchenko@...ux.intel.com> wrote:
> > > > > On Tue, Aug 22, 2023 at 09:51:21AM +0200, Bartosz Golaszewski wrote:

...

> > > > > > +static void gpio_sim_dispose_mappings(void *data)
> > > > > > +{
> > > > > > +     struct gpio_sim_chip *chip = data;
> > > > > > +     unsigned int i, irq;
> > > > > > +
> > > > > > +     for (i = 0; i < chip->gc.ngpio; i++) {
> > > > > > +             irq = irq_find_mapping(chip->irq_sim, i);
> > > > >
> > > > > > +             if (irq)
> > > > >
> > > > > This duplicates check in the following call.
> > > > >
> > > >
> > > > Ah so it can be a direct call:
> > > >
> > > >     irq_dispose_mapping(irq_find_mapping(chip->irq_sim, i));
> > > >
> > > > ?
> > >
> > > Hehe, seems yes and no. According to the code — yes, but code seems buggy,
> > > and compiler may effectively drop the check (haven't checked this, though).
> > >
> > > OTOH, the problem may appear if and only if we have no sparse IRQ configuration
> > > which is probably rare.
> > >
> > > That said, I will go without check, it's not your issue.
> > > And I found other places in IRQ framework that misses that check.
> > >
> > 
> > I disagree. If there's no strong contract from the provider of this
> > function then this check is so cheap that I'm ready to live with it.
> 
> There are plenty of calls that don't check and there are calls that check.
> 
> > > > > > +                     irq_dispose_mapping(irq);
> > > > > > +     }
> > > > > > +}

FWIW, I have checked the assembly and since virq is not a pointer, it has been
checked anyways. Hence I'm 100% sure the dup test is not needed and there is no
bug in the irq_dispose_mapping(). Just a bit hard to read.

-- 
With Best Regards,
Andy Shevchenko