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Message-ID: <9ddf5ebe-3bc1-2ddd-c36e-79d8ee1034e0@electromag.com.au>
Date: Mon, 16 Apr 2018 13:19:05 +0800
From: Phil Reid <preid@...ctromag.com.au>
To: Laura Abbott <labbott@...hat.com>,
Linus Walleij <linus.walleij@...aro.org>, Kees Cook <keescook@...omium.org>,
Lukas Wunner <lukas@...ner.de>, Rasmus Villemoes <linux@...musvillemoes.dk>
Cc: linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel-hardening@...ts.openwall.com
Subject: Re: [PATCHv5] gpio: Remove VLA from gpiolib
G'day Laura,
One more comment.
On 16/04/2018 12:41, Phil Reid wrote:
> 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@...ner.de>
>> Signed-off-by: Lukas Wunner <lukas@...ner.de>
>> Signed-off-by: Laura Abbott <labbott@...hat.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 v5: Dropped some outdated comments and extra whitespace.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
Also wouldn't this mean that fast path will never be triggered now...
>> +
>> /* 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@...ctromag.com.au
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