2023-08-10 11:55:50

by Bartosz Golaszewski

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

From: Bartosz Golaszewski <[email protected]>

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 <[email protected]>
---
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

2023-08-10 13:03:11

by Linus Walleij

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

On Thu, Aug 10, 2023 at 12:03 PM Bartosz Golaszewski <[email protected]> wrote:

> From: Bartosz Golaszewski <[email protected]>
>
> 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 <[email protected]>

Looks good to me!
Reviewed-by: Linus Walleij <[email protected]>

Yours,
Linus Walleij

2023-08-10 15:43:06

by Andy Shevchenko

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

On Thu, Aug 10, 2023 at 12:03:34PM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <[email protected]>
>
> 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

2023-08-10 15:57:59

by Andy Shevchenko

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

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 <[email protected]>

...

> > 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