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SubjectRe: [PATCHv5] gpio: Remove VLA from gpiolib
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G'day Laura,

On 14/04/2018 05:24, Laura Abbott wrote:
> The new challenge is to remove VLAs from the kernel
> (see https://lkml.org/lkml/2018/3/7/621) to eventually
> turn on -Wvla.
>
> Using a kmalloc array is the easy way to fix this but kmalloc is still
> more expensive than stack allocation. Introduce a fast path with a
> fixed size stack array to cover most chip with gpios below some fixed
> amount. The slow path dynamically allocates an array to cover those
> chips with a large number of gpios.
>
> Reviewed-and-tested-by: Lukas Wunner <lukas@wunner.de>
> Signed-off-by: Lukas Wunner <lukas@wunner.de>
> Signed-off-by: Laura Abbott <labbott@redhat.com>
> ---
> v5: Dropped some outdated comments and extra whitespace. Switched to
> ARCH_NR_GPIOS per suggestion of Linus Walleij.
> ---
> drivers/gpio/gpiolib.c | 76 +++++++++++++++++++++++++++++++++----------
> drivers/gpio/gpiolib.h | 2 +-
> include/linux/gpio/consumer.h | 10 +++---
> 3 files changed, 66 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index d66de67ef307..79ec7a29b684 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -61,6 +61,11 @@ static struct bus_type gpio_bus_type = {
> .name = "gpio",
> };
>
> +/*
> + * Number of GPIOs to use for the fast path in set array
> + */
> +#define FASTPATH_NGPIO ARCH_NR_GPIOS
> +
> /* gpio_lock prevents conflicts during gpio_desc[] table updates.
> * While any GPIO is requested, its gpio_chip is not removable;
> * each GPIO's "requested" flag serves as a lock and refcount.
> @@ -399,12 +404,11 @@ static long linehandle_ioctl(struct file *filep, unsigned int cmd,
> vals[i] = !!ghd.values[i];
>
> /* Reuse the array setting function */
> - gpiod_set_array_value_complex(false,
> + return gpiod_set_array_value_complex(false,
> true,
> lh->numdescs,
> lh->descs,
> vals);
> - return 0;
> }
> return -EINVAL;
> }
> @@ -1192,6 +1196,10 @@ int gpiochip_add_data_with_key(struct gpio_chip *chip, void *data,
> goto err_free_descs;
> }
>
> + if (chip->ngpio > FASTPATH_NGPIO)
> + chip_warn(chip, "line cnt %d is greater than fast path cnt %d\n",
> + chip->ngpio, FASTPATH_NGPIO);
> +
> gdev->label = kstrdup_const(chip->label ?: "unknown", GFP_KERNEL);
> if (!gdev->label) {
> status = -ENOMEM;
> @@ -2662,16 +2670,28 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep,
>
> while (i < array_size) {
> struct gpio_chip *chip = desc_array[i]->gdev->chip;
> - unsigned long mask[BITS_TO_LONGS(chip->ngpio)];
> - unsigned long bits[BITS_TO_LONGS(chip->ngpio)];
> + unsigned long fastpath[2 * BITS_TO_LONGS(FASTPATH_NGPIO)];
> + unsigned long *mask, *bits;
> int first, j, ret;
>
> + if (likely(chip->ngpio <= FASTPATH_NGPIO)) {
> + memset(fastpath, 0, sizeof(fastpath));
> + mask = fastpath;
> + bits = fastpath + BITS_TO_LONGS(FASTPATH_NGPIO);
Previously it looks like just mask was zeroed.
So could this just be:
memset(mask, 0, BITS_TO_LONGS(chip->ngpio));

I'm guessing it's not a huge additional overhead as it is, but it's more in line with what was there.


> + } else {
> + mask = kcalloc(2 * BITS_TO_LONGS(chip->ngpio),
> + sizeof(*mask),
> + can_sleep ? GFP_KERNEL : GFP_ATOMIC);
> + if (!mask)
> + return -ENOMEM;
> + bits = mask + BITS_TO_LONGS(chip->ngpio);
> + }
> +
> if (!can_sleep)
> WARN_ON(chip->can_sleep);
>
> /* collect all inputs belonging to the same chip */
> first = i;
> - memset(mask, 0, sizeof(mask));
> do {
> const struct gpio_desc *desc = desc_array[i];
> int hwgpio = gpio_chip_hwgpio(desc);
> @@ -2682,8 +2702,11 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep,
> (desc_array[i]->gdev->chip == chip));
>
> ret = gpio_chip_get_multiple(chip, mask, bits);
> - if (ret)
> + if (ret) {
> + if (mask != fastpath)
> + kfree(mask);
> return ret;
> + }
>
> for (j = first; j < i; j++) {
> const struct gpio_desc *desc = desc_array[j];
> @@ -2695,6 +2718,9 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep,
> value_array[j] = value;
> trace_gpio_value(desc_to_gpio(desc), 1, value);
> }
> +
> + if (mask != fastpath)
> + kfree(mask);
> }
> return 0;
> }
> @@ -2878,7 +2904,7 @@ static void gpio_chip_set_multiple(struct gpio_chip *chip,
> }
> }
>
> -void gpiod_set_array_value_complex(bool raw, bool can_sleep,
> +int gpiod_set_array_value_complex(bool raw, bool can_sleep,
> unsigned int array_size,
> struct gpio_desc **desc_array,
> int *value_array)
> @@ -2887,14 +2913,26 @@ void gpiod_set_array_value_complex(bool raw, bool can_sleep,
>
> while (i < array_size) {
> struct gpio_chip *chip = desc_array[i]->gdev->chip;
> - unsigned long mask[BITS_TO_LONGS(chip->ngpio)];
> - unsigned long bits[BITS_TO_LONGS(chip->ngpio)];
> + unsigned long fastpath[2 * BITS_TO_LONGS(FASTPATH_NGPIO)];
> + unsigned long *mask, *bits;
> int count = 0;
>
> + if (likely(chip->ngpio <= FASTPATH_NGPIO)) {
> + memset(fastpath, 0, sizeof(fastpath));
> + mask = fastpath;
> + bits = fastpath + BITS_TO_LONGS(FASTPATH_NGPIO);
> + } else {
> + mask = kcalloc(2 * BITS_TO_LONGS(chip->ngpio),
> + sizeof(*mask),
> + can_sleep ? GFP_KERNEL : GFP_ATOMIC);
> + if (!mask)
> + return -ENOMEM;
> + bits = mask + BITS_TO_LONGS(chip->ngpio);
> + }
> +
> if (!can_sleep)
> WARN_ON(chip->can_sleep);
>
> - memset(mask, 0, sizeof(mask));
> do {
> struct gpio_desc *desc = desc_array[i];
> int hwgpio = gpio_chip_hwgpio(desc);
> @@ -2925,7 +2963,11 @@ void gpiod_set_array_value_complex(bool raw, bool can_sleep,
> /* push collected bits to outputs */
> if (count != 0)
> gpio_chip_set_multiple(chip, mask, bits);
> +
> + if (mask != fastpath)
> + kfree(mask);
> }
> + return 0;
> }
>
> /**
> @@ -3000,13 +3042,13 @@ EXPORT_SYMBOL_GPL(gpiod_set_value);
> * This function should be called from contexts where we cannot sleep, and will
> * complain if the GPIO chip functions potentially sleep.
> */
> -void gpiod_set_raw_array_value(unsigned int array_size,
> +int gpiod_set_raw_array_value(unsigned int array_size,
> struct gpio_desc **desc_array, int *value_array)
> {
> if (!desc_array)
> - return;
> - gpiod_set_array_value_complex(true, false, array_size, desc_array,
> - value_array);
> + return -EINVAL;
> + return gpiod_set_array_value_complex(true, false, array_size,
> + desc_array, value_array);
> }
> EXPORT_SYMBOL_GPL(gpiod_set_raw_array_value);
>
> @@ -3326,14 +3368,14 @@ EXPORT_SYMBOL_GPL(gpiod_set_value_cansleep);
> *
> * This function is to be called from contexts that can sleep.
> */
> -void gpiod_set_raw_array_value_cansleep(unsigned int array_size,
> +int gpiod_set_raw_array_value_cansleep(unsigned int array_size,
> struct gpio_desc **desc_array,
> int *value_array)
> {
> might_sleep_if(extra_checks);
> if (!desc_array)
> - return;
> - gpiod_set_array_value_complex(true, true, array_size, desc_array,
> + return -EINVAL;
> + return gpiod_set_array_value_complex(true, true, array_size, desc_array,
> value_array);
> }
> EXPORT_SYMBOL_GPL(gpiod_set_raw_array_value_cansleep);
> diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
> index b17ec6795c81..b64813e3876e 100644
> --- a/drivers/gpio/gpiolib.h
> +++ b/drivers/gpio/gpiolib.h
> @@ -188,7 +188,7 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep,
> unsigned int array_size,
> struct gpio_desc **desc_array,
> int *value_array);
> -void gpiod_set_array_value_complex(bool raw, bool can_sleep,
> +int gpiod_set_array_value_complex(bool raw, bool can_sleep,
> unsigned int array_size,
> struct gpio_desc **desc_array,
> int *value_array);
> diff --git a/include/linux/gpio/consumer.h b/include/linux/gpio/consumer.h
> index dbd065963296..243112c7fa7d 100644
> --- a/include/linux/gpio/consumer.h
> +++ b/include/linux/gpio/consumer.h
> @@ -116,7 +116,7 @@ int gpiod_get_raw_array_value(unsigned int array_size,
> struct gpio_desc **desc_array,
> int *value_array);
> void gpiod_set_raw_value(struct gpio_desc *desc, int value);
> -void gpiod_set_raw_array_value(unsigned int array_size,
> +int gpiod_set_raw_array_value(unsigned int array_size,
> struct gpio_desc **desc_array,
> int *value_array);
>
> @@ -134,7 +134,7 @@ int gpiod_get_raw_array_value_cansleep(unsigned int array_size,
> struct gpio_desc **desc_array,
> int *value_array);
> void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value);
> -void gpiod_set_raw_array_value_cansleep(unsigned int array_size,
> +int gpiod_set_raw_array_value_cansleep(unsigned int array_size,
> struct gpio_desc **desc_array,
> int *value_array);
>
> @@ -369,12 +369,13 @@ static inline void gpiod_set_raw_value(struct gpio_desc *desc, int value)
> /* GPIO can never have been requested */
> WARN_ON(1);
> }
> -static inline void gpiod_set_raw_array_value(unsigned int array_size,
> +static inline int gpiod_set_raw_array_value(unsigned int array_size,
> struct gpio_desc **desc_array,
> int *value_array)
> {
> /* GPIO can never have been requested */
> WARN_ON(1);
> + return 0;
> }
>
> static inline int gpiod_get_value_cansleep(const struct gpio_desc *desc)
> @@ -423,12 +424,13 @@ static inline void gpiod_set_raw_value_cansleep(struct gpio_desc *desc,
> /* GPIO can never have been requested */
> WARN_ON(1);
> }
> -static inline void gpiod_set_raw_array_value_cansleep(unsigned int array_size,
> +static inline int gpiod_set_raw_array_value_cansleep(unsigned int array_size,
> struct gpio_desc **desc_array,
> int *value_array)
> {
> /* GPIO can never have been requested */
> WARN_ON(1);
> + return 0;
> }
>
> static inline int gpiod_set_debounce(struct gpio_desc *desc, unsigned debounce)
>


--
Regards
Phil Reid

ElectroMagnetic Imaging Technology Pty Ltd
Development of Geophysical Instrumentation & Software
www.electromag.com.au

3 The Avenue, Midland WA 6056, AUSTRALIA
Ph: +61 8 9250 8100
Fax: +61 8 9250 7100
Email: preid@electromag.com.au

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