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

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

[Bartosz Golaszewski]

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'm going through the resource management issues one-by-one using the
new virtual consumer module. This is something I found when I noticed
that IDA numbers never get freed for a chip that was removed with descs
still in use.

 drivers/gpio/gpiolib.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 251c875b5c34..7408e2561b2d 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -2167,12 +2167,14 @@ 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 {
+	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

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

[Linus Walleij]

On Thu, Aug 10, 2023 at 12:03 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>

Looks good to me!
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Yours,
Linus Walleij

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

[Andy Shevchenko]

On Thu, Aug 10, 2023 at 12:03:34PM +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

...

>  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 {
> +	if (!desc)
> +		return;

	VALIDATE_DESC_VOID() ?

> +	if (!gpiod_free_commit(desc))
>  		WARN_ON(extra_checks);
> -	}
> +
> +	gpio_device_put(desc->gdev);
> +	module_put(desc->gdev->owner);
>  }

-- 
With Best Regards,
Andy Shevchenko

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

[Andy Shevchenko]

On Thu, Aug 10, 2023 at 06:17:26PM +0300, Andy Shevchenko wrote:
> On Thu, Aug 10, 2023 at 12:03:34PM +0200, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

...

> >  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 {
> > +	if (!desc)
> > +		return;

> 	VALIDATE_DESC_VOID() ?

If it is not possible to use, the comment should be added, like we have in
gpiod_to_irq().

> > +	if (!gpiod_free_commit(desc))
> >  		WARN_ON(extra_checks);
> > -	}
> > +
> > +	gpio_device_put(desc->gdev);
> > +	module_put(desc->gdev->owner);
> >  }

-- 
With Best Regards,
Andy Shevchenko