linux-kernel - Re: [PATCH v2] gpiolib: fix reference leaks when removing GPIO chips still in use

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Message-ID: <CAMRc=MerfgEWM+P3MMUF3r73jwEVe09Es9B13Erz4-2qL=PNsQ@mail.gmail.com>
Date:   Fri, 11 Aug 2023 21:27:20 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Kent Gibson <warthog618@...il.com>
Cc:     linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v2] gpiolib: fix reference leaks when removing GPIO chips
 still in use

On Fri, Aug 11, 2023 at 1:57 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
>
> On Thu, Aug 10, 2023 at 8:48 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
> >
> > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> >
> > After we remove a GPIO chip that still has some requested descriptors,
> > gpiod_free_commit() will fail and we will never put the references to the
> > GPIO device and the owning module in gpiod_free().
> >
> > Rework this function to:
> > - not warn on desc == NULL as this is a use-case on which most free
> >   functions silently return
> > - put the references to desc->gdev and desc->gdev->owner unconditionally
> >   so that the release callback actually gets called when the remaining
> >   references are dropped by external GPIO users
> >
> > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > ---
> > v1 -> v2:
> > - add a comment about why we can't use VALIDATE_DESC_VOID()
> >
> >  drivers/gpio/gpiolib.c | 16 +++++++++++-----
> >  1 file changed, 11 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> > index 251c875b5c34..2158067c4fd2 100644
> > --- a/drivers/gpio/gpiolib.c
> > +++ b/drivers/gpio/gpiolib.c
> > @@ -2167,12 +2167,18 @@ static bool gpiod_free_commit(struct gpio_desc *desc)
> >
> >  void gpiod_free(struct gpio_desc *desc)
> >  {
> > -       if (desc && desc->gdev && gpiod_free_commit(desc)) {
> > -               module_put(desc->gdev->owner);
> > -               gpio_device_put(desc->gdev);
> > -       } else {
> > +       /*
> > +        * We must not use VALIDATE_DESC_VOID() as the underlying gdev->chip
> > +        * may already be NULL but we still want to put the references.
> > +        */
> > +       if (!desc)
> > +               return;
> > +
> > +       if (!gpiod_free_commit(desc))
> >                 WARN_ON(extra_checks);
> > -       }
> > +
> > +       gpio_device_put(desc->gdev);
> > +       module_put(desc->gdev->owner);
> >  }
> >
> >  /**
> > --
> > 2.39.2
> >
>
> Queued for fixes.
>
> Bartosz

Eek, I need to back it out. I realized there's an issue with this
patch. I'll send a v3.

Bartosz