Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCHv5] gpio: Remove VLA from gpiolib
From:   Phil Reid <preid@electromag.com.au>
To:     Laura Abbott <labbott@redhat.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Kees Cook <keescook@chromium.org>,
        Lukas Wunner <lukas@wunner.de>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc:     linux-gpio@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-hardening@lists.openwall.com
References: <20180413212427.18261-1-labbott@redhat.com>
 <b325f426-b491-4f95-f89d-1189f91d97f5@electromag.com.au>
Message-ID: <9ddf5ebe-3bc1-2ddd-c36e-79d8ee1034e0@electromag.com.au>
Date:   Mon, 16 Apr 2018 13:19:05 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101
 Thunderbird/52.7.0
MIME-Version: 1.0
In-Reply-To: <b325f426-b491-4f95-f89d-1189f91d97f5@electromag.com.au>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-AU
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@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 v5: Dropped some outdated comments and extra whitespace.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

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@electromag.com.au