diff mbox series

[16/22] gpio: reduce the functionality of validate_desc()

Message ID 20240130124828.14678-17-brgl@bgdev.pl
State New
Headers show
Series gpio: rework locking and object life-time control | expand

Commit Message

Bartosz Golaszewski Jan. 30, 2024, 12:48 p.m. UTC 
From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Checking desc->gdev->chip for NULL without holding it in place with some
serializing mechanism is pointless. Remove this check. Also don't check
desc->gdev for NULL as it can never happen.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
 drivers/gpio/gpiolib.c | 18 +++---------------
 1 file changed, 3 insertions(+), 15 deletions(-)

Comments

Linus Walleij Jan. 31, 2024, 8:16 p.m. UTC | #1 
On Tue, Jan 30, 2024 at 1:48 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:

> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>
> Checking desc->gdev->chip for NULL without holding it in place with some
> serializing mechanism is pointless. Remove this check. Also don't check
> desc->gdev for NULL as it can never happen.
>
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

I don't know if I agree that it is pointless. It will work on any single-CPU
system and 99.9% of other cases.

On the other hand: what it is supposed to protect against is userspace
doing calls to a gpio_device through the character device, while the
backing struct gpio_chip is gone (e.g. a GPIO expander on USB,
and someone pulled the cable), i.e. it became NULL, and this is why the
error message says "backing device is gone".

But I want to see where the series is going, maybe you fix this
problem in the end, so I can come back and ACK this.

Yours,
Linus Walleij
Linus Walleij Jan. 31, 2024, 8:19 p.m. UTC | #2 
On Wed, Jan 31, 2024 at 9:16 PM Linus Walleij <linus.walleij@linaro.org> wrote:
> On Tue, Jan 30, 2024 at 1:48 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
>
> > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
> >
> > Checking desc->gdev->chip for NULL without holding it in place with some
> > serializing mechanism is pointless. Remove this check. Also don't check
> > desc->gdev for NULL as it can never happen.
> >
> > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>
> I don't know if I agree that it is pointless. It will work on any single-CPU
> system and 99.9% of other cases.
>
> On the other hand: what it is supposed to protect against is userspace
> doing calls to a gpio_device through the character device, while the
> backing struct gpio_chip is gone (e.g. a GPIO expander on USB,
> and someone pulled the cable), i.e. it became NULL, and this is why the
> error message says "backing device is gone".
>
> But I want to see where the series is going, maybe you fix this
> problem in the end, so I can come back and ACK this.

Aha, it is fixed in patches 19+20. Maybe mention that we add a new
protection later in the series in the commit message?

Anyway, I get it now!

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Yours,
Linus Walleij
diff mbox series

Patch

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index ddf7d93f8b76..0cb44578bc72 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -2248,19 +2248,12 @@  static int validate_desc(const struct gpio_desc *desc, const char *func)
 {
 	if (!desc)
 		return 0;
+
 	if (IS_ERR(desc)) {
 		pr_warn("%s: invalid GPIO (errorpointer)\n", func);
 		return PTR_ERR(desc);
 	}
-	if (!desc->gdev) {
-		pr_warn("%s: invalid GPIO (no device)\n", func);
-		return -EINVAL;
-	}
-	if (!desc->gdev->chip) {
-		dev_warn(&desc->gdev->dev,
-			 "%s: backing chip is gone\n", func);
-		return 0;
-	}
+
 	return 1;
 }
 
@@ -2336,12 +2329,7 @@  static bool gpiod_free_commit(struct gpio_desc *desc)
 
 void gpiod_free(struct gpio_desc *desc)
 {
-	/*
-	 * 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;
+	VALIDATE_DESC_VOID(desc);
 
 	if (!gpiod_free_commit(desc))
 		WARN_ON(1);