Subject: Re: [PATCH 2/2] gpio: gpiolib: set gpiochip_remove retval to void

From: Lars-Peter Clausen <[email-masked]>
Date: Sat, 31 May 2014 09:35:39 +0200

On 05/31/2014 01:29 AM, Greg KH wrote:
> On Fri, May 30, 2014 at 08:16:59PM +0200, Lars-Peter Clausen wrote:
>> On 05/30/2014 07:33 PM, David Daney wrote:
>>> On 05/30/2014 04:39 AM, Geert Uytterhoeven wrote:
>>>> On Fri, May 30, 2014 at 1:30 PM, abdoulaye berthe <[email-masked]>
>>>> wrote:
>>>>> --- a/drivers/gpio/gpiolib.c
>>>>> +++ b/drivers/gpio/gpiolib.c
>>>>> @@ -1263,10 +1263,9 @@ static void gpiochip_irqchip_remove(struct
>>>>> gpio_chip *gpiochip);
>>>>>    *
>>>>>    * A gpio_chip with any GPIOs still requested may not be removed.
>>>>>    */
>>>>> -int gpiochip_remove(struct gpio_chip *chip)
>>>>> +void gpiochip_remove(struct gpio_chip *chip)
>>>>>   {
>>>>>          unsigned long   flags;
>>>>> -       int             status = 0;
>>>>>          unsigned        id;
>>>>>
>>>>>          acpi_gpiochip_remove(chip);
>>>>> @@ -1278,24 +1277,15 @@ int gpiochip_remove(struct gpio_chip *chip)
>>>>>          of_gpiochip_remove(chip);
>>>>>
>>>>>          for (id = 0; id < chip->ngpio; id++) {
>>>>> -               if (test_bit(FLAG_REQUESTED, &chip->desc[id].flags)) {
>>>>> -                       status = -EBUSY;
>>>>> -                       break;
>>>>> -               }
>>>>> -       }
>>>>> -       if (status == 0) {
>>>>> -               for (id = 0; id < chip->ngpio; id++)
>>>>> -                       chip->desc[id].chip = NULL;
>>>>> -
>>>>> -               list_del(&chip->list);
>>>>> +               if (test_bit(FLAG_REQUESTED, &chip->desc[id].flags))
>>>>> +                       panic("gpio: removing gpiochip with gpios still
>>>>> requested\n");
>>>>
>>>> panic?
>>>
>>> NACK to the patch for this reason.  The strongest thing you should do here
>>> is WARN.
>>>
>>> That said, I am not sure why we need this whole patch set in the first place.
>>
>> Well, what currently happens when you remove a device that is a provider of
>> a gpio_chip which is still in use, is that the kernel crashes. Probably with
>> a rather cryptic error message. So this patch doesn't really change the
>> behavior, but makes it more explicit what is actually wrong. And even if you
>> replace the panic() by a WARN() it will again just crash slightly later.
>>
>> This is a design flaw in the GPIO subsystem that needs to be fixed.
>
> Then fix the GPIO code properly, don't add a new panic() to the kernel.

Until somebody comes up with a patch that fixes this for good I think that 
patch is still an improvement over the current situation. Rather than 
keeping the kernel running in a inconsistent state, which might cause all 
kinds of undefined behavior and which will lead to a crash eventually, we 
might as well just crash the kernel at the cause of the inconsistent state. 
This will make it obvious why it crashed (compared to a random stacktrace) 
and will also prevent the kernel from running in a undefined state.

- Lars