[PATCH] gpiolib: allocate memory atomically with a spinlock held

[PATCH] gpiolib: allocate memory atomically with a spinlock held

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

We will eventually switch to protecting the GPIO descriptors with a mutex
but until then, we need to allocate memory for the label copy atomically
while we're holding the global spinlock.

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/linux-gpio/62588146-eed6-42f7-ba26-160226b109fe@moroto.mountain/T/#u
Fixes: f8d05e276b45 ("gpiolib: remove gpiochip_is_requested()")
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
 drivers/gpio/gpiolib.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 4e190be75dc2..6efe44570333 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -2399,7 +2399,15 @@ char *gpiochip_dup_line_label(struct gpio_chip *gc, unsigned int offset)
 	if (!test_bit(FLAG_REQUESTED, &desc->flags))
 		return NULL;
 
-	label = kstrdup(desc->label, GFP_KERNEL);
+	/*
+	 * FIXME: Once we mark gpiod_direction_input/output() and
+	 * gpiod_get_direction() with might_sleep(), we'll be able to protect
+	 * the GPIO descriptors with mutex (while value setting operations will
+	 * become lockless).
+	 *
+	 * Until this happens, this allocation needs to be atomic.
+	 */
+	label = kstrdup(desc->label, GFP_ATOMIC);
 	if (!label)
 		return ERR_PTR(-ENOMEM);
 
-- 
2.40.1

Re: [PATCH] gpiolib: allocate memory atomically with a spinlock held

[Linus Walleij]

On Tue, Dec 12, 2023 at 11:55 AM Bartosz Golaszewski <brgl@bgdev.pl> wrote:

> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>
> We will eventually switch to protecting the GPIO descriptors with a mutex
> but until then, we need to allocate memory for the label copy atomically
> while we're holding the global spinlock.
>
> Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
> Closes: https://lore.kernel.org/linux-gpio/62588146-eed6-42f7-ba26-160226b109fe@moroto.mountain/T/#u
> Fixes: f8d05e276b45 ("gpiolib: remove gpiochip_is_requested()")
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

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

Yours,
Linus Walleij

Re: [PATCH] gpiolib: allocate memory atomically with a spinlock held

[Bartosz Golaszewski]

On Tue, Dec 12, 2023 at 11:55 AM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
>
> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>
> We will eventually switch to protecting the GPIO descriptors with a mutex
> but until then, we need to allocate memory for the label copy atomically
> while we're holding the global spinlock.
>
> Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
> Closes: https://lore.kernel.org/linux-gpio/62588146-eed6-42f7-ba26-160226b109fe@moroto.mountain/T/#u
> Fixes: f8d05e276b45 ("gpiolib: remove gpiochip_is_requested()")
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
> ---
>  drivers/gpio/gpiolib.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 4e190be75dc2..6efe44570333 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -2399,7 +2399,15 @@ char *gpiochip_dup_line_label(struct gpio_chip *gc, unsigned int offset)
>         if (!test_bit(FLAG_REQUESTED, &desc->flags))
>                 return NULL;
>
> -       label = kstrdup(desc->label, GFP_KERNEL);
> +       /*
> +        * FIXME: Once we mark gpiod_direction_input/output() and
> +        * gpiod_get_direction() with might_sleep(), we'll be able to protect
> +        * the GPIO descriptors with mutex (while value setting operations will
> +        * become lockless).
> +        *
> +        * Until this happens, this allocation needs to be atomic.
> +        */
> +       label = kstrdup(desc->label, GFP_ATOMIC);
>         if (!label)
>                 return ERR_PTR(-ENOMEM);
>
> --
> 2.40.1
>

Patch applied.

Bart