[v2] gpiolib: fix reference leaks when removing GPIO chips still in use

  From: Bartosz Golaszewski <bartosz.golaszewski@linaro.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@linaro.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(-)
  

On Thu, Aug 10, 2023 at 8:48 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
>
> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.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@linaro.org>

I forgot to pick up Linus' tag. I'll do it when applying. I should
really start using b4...

Bart

> ---
> 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
>
  

On Thu, Aug 10, 2023 at 8:58 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:

> I forgot to pick up Linus' tag. I'll do it when applying. I should
> really start using b4...

Well with b4 you still have to issue b4 trailers -u, I almost want to
make a cron script that just loop over my b4 branches and do that
every night when I'm asleep so tags get picked up in case I miss
them.

Hm, maybe not such a bad idea.

Yours,
Linus Walleij
  

On Thu, Aug 10, 2023 at 08:48:46PM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.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

...

> +	/*
> +	 * We must not use VALIDATE_DESC_VOID() as the underlying gdev->chip
> +	 * may already be NULL but we still want to put the references.
> +	 */

Clear now!

...

> +	if (!gpiod_free_commit(desc))
>  		WARN_ON(extra_checks);

	/* Always call gpiod_free_commit() */
	WARN_ON(!gpiod_free_commit(desc) && extra_checks);

?
  

On Thu, Aug 10, 2023 at 8:48 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
>
> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.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@linaro.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
  

On Fri, Aug 11, 2023 at 1:57 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
>
> On Thu, Aug 10, 2023 at 8:48 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
> >
> > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.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@linaro.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