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

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Date: Fri, 15 Dec 2023 16:43:50 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Linus Walleij <linus.walleij@...aro.org>, 
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Kent Gibson <warthog618@...il.com>
Cc: linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>, Dan Carpenter <dan.carpenter@...aro.org>
Subject: Re: [PATCH] gpiolib: allocate memory atomically with a spinlock held

On Tue, Dec 12, 2023 at 11:55 AM Bartosz Golaszewski <brgl@...ev.pl> wrote:
>
> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.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@...aro.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@...aro.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