Re: [RFC PATCH] gpiolib: fix oops, if gpio name is NULL

[Vladimir Zapolskiy <vz@mleia.com>]

Hi Linus,

On 17.11.2015 13:50, Markus Pargmann wrote:
> Hi Vladimir,
> 
> On Tuesday 17 November 2015 13:20:40 Vladimir Zapolskiy wrote:
>> Hi Markus,
>>
>> On 17.11.2015 11:24, Markus Pargmann wrote:
>>> Hi,
>>>
>>> On Wednesday 11 November 2015 14:36:53 Vladimir Zapolskiy wrote:
>>>> Commit c0017ed71966 ("gpio: Introduce gpio descriptor 'name'") causes
>>>> OOPS on boot on LPC32xx boards:
>>>>
>>>>     Unable to handle kernel NULL pointer dereference at virtual address 00000000
>>>>     CPU: 0 PID: 1 Comm: swapper Not tainted 4.3.0+ #707
>>>>     Hardware name: LPC32XX SoC (Flattened Device Tree)
>>>>     task: c381baa0 ti: c381e000 task.ti: c381e000
>>>>     PC is at strcmp+0x10/0x40
>>>>     LR is at gpiochip_add+0x3d0/0x4d4
>>>>     pc : [<>]    lr : [<>]    psr: a0000093
>>>>     sp : c381fd60  ip : c381fd70  fp : c381fd6c
>>>>
>>>>     [snip]
>>>>
>>>>     Backtrace:
>>>>     [<>] (strcmp) from [<>] (gpiochip_add+0x3d0/0x4d4)
>>>>     [<>] (gpiochip_add) from [<>] (lpc32xx_gpio_probe+0x44/0x60)
>>>>     [<>] (lpc32xx_gpio_probe) from [<>] (platform_drv_probe+0x40/0x8c)
>>>>     [<>] (platform_drv_probe) from [<>] (driver_probe_device+0x110/0x294)
>>>>     [<>] (driver_probe_device) from [<>] (__driver_attach+0x70/0x94)
>>>>     [<>] (__driver_attach) from [<>] (bus_for_each_dev+0x74/0x98)
>>>>     [<>] (bus_for_each_dev) from [<>] (driver_attach+0x20/0x28)
>>>>     [<>] (driver_attach) from [<>] (bus_add_driver+0xd4/0x1f0)
>>>>     [<>] (bus_add_driver) from [<>] (driver_register+0xa4/0xe8)
>>>>     [<>] (driver_register) from [<>] (__platform_driver_register+0x38/0x4c)
>>>>     [<>] (__platform_driver_register) from [<>] (lpc32xx_gpio_driver_init+0x18/0x20)
>>>>     [<>] (lpc32xx_gpio_driver_init) from [<>] (do_one_initcall+0x108/0x1c8)
>>>>     [<>] (do_one_initcall) from [<>] (kernel_init_freeable+0x10c/0x1d4)
>>>>     [<>] (kernel_init_freeable) from [<>] (kernel_init+0x10/0xec)
>>>>     [<>] (kernel_init) from [<>] (ret_from_fork+0x14/0x24)
>>>>
>>>> This is caused by the fact that at the moment some GPIO names are set
>>>> to NULL, there is a hole in linear representation of one GPI bank, see
>>>> drivers/gpio/gpio-lpc32xx.c / gpi_p3_names[] for details.
>>>>
>>>> The same problem most probably affects also gpio-cs5535.c, see
>>>> cs5535_gpio_names[].
>>>>
>>>> Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
>>>> ---
>>>> Linus, Markus,
>>>>
>>>> I understand that LPC32xx GPIO driver is ugly (hopefully this
>>>> will be changed in future), but please account this problem.
>>>>
>>>> I don't ask for inclusion of this change, because my own analysis is
>>>> not done completely.
>>>>
>>>> Also please review, the same problem probably affects gpio-cs5535.c
>>>> as well, see cs5535_gpio_names[].
>>>
>>> Thanks for this hint. But I think these patches for gpio_name_to_desc won't get
>>> mainline any time soon as this depends on the chardev interface and how it will
>>> look like.
>>>
>>
>> sorry for misunderstanding, what do mean by "these patches"?
>>
>> I see two options here, one is to fix or revert your c0017ed71966 due to
>> caused regressions, another one is to update affected GPIO drivers
>> removing discontinuity in GPIO enumeration inside a bank.
> 
> Sorry, seems I was on a wrong kernel version when checking this morning. Linus
> removed lots of my patches from his tree after some correct comments so I
> thought this patch was removed as well.

Linus, should I resend this fix for v4.4 or is it good enough for
application?

> As it is mainline your patch looks good to me. Perhaps a comment on why we need
> to check for !name at this point would be good.

There is such a description in the commit message, why this check is needed.

With best wishes,
Vladimir

> Best Regards,
> 
> Markus
> 
>>
>> With best wishes,
>> Vladimir
>>
>>>>
>>>>  drivers/gpio/gpiolib.c | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
>>>> index a18f00f..2a91f32 100644
>>>> --- a/drivers/gpio/gpiolib.c
>>>> +++ b/drivers/gpio/gpiolib.c
>>>> @@ -233,7 +233,7 @@ static struct gpio_desc *gpio_name_to_desc(const char * const name)
>>>>  		for (i = 0; i != chip->ngpio; ++i) {
>>>>  			struct gpio_desc *gpio = &chip->desc[i];
>>>>  
>>>> -			if (!gpio->name)
>>>> +			if (!gpio->name || !name)
>>>>  				continue;
>>>>  
>>>>  			if (!strcmp(gpio->name, name)) {
>>>>
>>>
>>
>