On 08/24/2013 01:48 PM, danielfsan...@att.net wrote:
I got this on an RPi and I can't find anything specific to that.
Besides, it's clearly wrong to try to access desc->chip when we have
just tested that it may be NULL at drivers/gpio/gpiolib.c:1409:
chip = desc->chip;
if (chip == NULL)
goto done;
....
done:
if (status)
pr_debug("_gpio_request: gpio-%d (%s) status %d\n",
desc_to_gpio(desc), label ? : "?", status);
To reproduce, just pick an invalid gpio nubmer and:
echo -n 248 > /sys/class/gpio/export
However, I wasn't able to reproduce it on my laptop, maybe because I
don't have any real gpio chips there, not sure. More info on RPi bug
report: https://github.com/raspberrypi/linux/issues/364
This fix makes sure that gpio_to_desc() only returns non-NULL if the
specified gpio really has a chip, and not just if it's within the ranged
of gpios for the arch.
[ 222.961384] Unable to handle kernel NULL pointer dereference at
virtual address 00000044
[ 222.969486] pgd = d97d0000
[ 222.972190] [00000044] *pgd=1aaca831, *pte=00000000, *ppte=00000000
[ 222.978483] Internal error: Oops: 17 [#1] PREEMPT ARM
---
drivers/gpio/gpiolib.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index d6413b2..db7c6bb 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -123,7 +123,8 @@ static int gpio_chip_hwgpio(const struct gpio_desc *desc)
*/
static struct gpio_desc *gpio_to_desc(unsigned gpio)
{
- if (WARN(!gpio_is_valid(gpio), "invalid GPIO %d\n", gpio))
+ if (WARN(!gpio_is_valid(gpio) || !gpio_desc[gpio].chip,
+ "invalid GPIO %d\n", gpio))
I think this triggers a WARN if someone requests an invalid gpio pin from
userspace.
Is this really a good idea ?
[ and then export_store and unexport_store complain again with pr_warn ]
May be a separate patch, but if the WARN is useful it might make sense to
introduce
gpio_to_desc_silent() which doesn't produce the WARN if it fails.
Looking further into the code, I suspect there may be some race condition
where desc->chip is not (yet) set and export_store is called. So we will
see a WARNING instead of a crash, as the underlying condition still exists.
return NULL;
else
return &gpio_desc[gpio];
@@ -1406,8 +1407,7 @@ static int gpiod_request(struct gpio_desc *desc, const
char *label)
spin_lock_irqsave(&gpio_lock, flags);
chip = desc->chip;
- if (chip == NULL)
- goto done;
+ BUG_ON(!chip);
... which in turn means we might see this one. If so, this code might replace
an invalid memory access crash with a BUG crash. Is this really desirable, or
should this better be a WARN ?
Guenter
if (!try_module_get(chip->owner))
goto done;
--
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