linux-kernel - Re: [PATCH] gpiolib: don't call sleeping functions with a spinlock taken

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Message-ID: <CAMRc=McrL9bZpMVFHt7e9zKzqCd1aMoPYSBd5WqXRmiDU3pL-w@mail.gmail.com>
Date:   Fri, 20 Mar 2020 17:55:06 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Geert Uytterhoeven <geert@...ux-m68k.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>
Subject: Re: [PATCH] gpiolib: don't call sleeping functions with a spinlock taken

pt., 20 mar 2020 o 11:59 Geert Uytterhoeven <geert@...ux-m68k.org> napisał(a):
>
> Hi Bartosz,
>
> On Fri, Mar 20, 2020 at 10:31 AM Bartosz Golaszewski <brgl@...ev.pl> wrote:
> > From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> >
> > We must not call pinctrl_gpio_can_use_line() with the gpio_lock taken
> > as it takes a mutex internally. Let's move the call before taking the
> > spinlock and store the return value.
> >
> > This isn't perfect - there's a moment between calling
> > pinctrl_gpio_can_use_line() and taking the spinlock where the situation
> > can change but it isn't a regression either: previously this part wasn't
> > protected at all and it only affects the information user-space is
> > seeing.
> >
> > Reported-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> > Fixes: d2ac25798208 ("gpiolib: provide a dedicated function for setting lineinfo")
> > Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
>
> Thanks for your patch!
>
> > --- a/drivers/gpio/gpiolib.c
> > +++ b/drivers/gpio/gpiolib.c
> > @@ -1154,8 +1154,19 @@ static void gpio_desc_to_lineinfo(struct gpio_desc *desc,
> >                                   struct gpioline_info *info)
> >  {
> >         struct gpio_chip *chip = desc->gdev->chip;
> > +       bool ok_for_pinctrl;
> >         unsigned long flags;
> >
> > +       /*
> > +        * This function takes a mutex so we must check this before taking
> > +        * the spinlock.
> > +        *
> > +        * FIXME: find a non-racy way to retrieve this information. Maybe a
> > +        * lock common to both frameworks?
> > +        */
> > +       ok_for_pinctrl = pinctrl_gpio_can_use_line(
> > +                               chip->base + info->line_offset);
>
> Note that this is now called unconditionally, while before it was only called
> if all previous steps in the ||-pipeline failed.
>

Is this a problem though? Doesn't seem so. Am I missing something?

Bart