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

[Markus Pargmann <mpa@pengutronix.de>]

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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.

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.

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)) {
> >>
> > 
> 

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