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gpiolib: fix oops in gpio_get_value_cansleep()

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We can get the following oops from gpio_get_value_cansleep() when a GPIO
controller doesn't provide a get() callback:

 Unable to handle kernel paging request for instruction fetch
 Faulting instruction address: 0x00000000
 Oops: Kernel access of bad area, sig: 11 [#1]
 [...]
 NIP [00000000] 0x0
 LR [c0182fb0] gpio_get_value_cansleep+0x40/0x50
 Call Trace:
 [c7b79e80] [c0183f28] gpio_value_show+0x5c/0x94
 [c7b79ea0] [c01a584c] dev_attr_show+0x30/0x7c
 [c7b79eb0] [c00d6b48] fill_read_buffer+0x68/0xe0
 [c7b79ed0] [c00d6c54] sysfs_read_file+0x94/0xbc
 [c7b79ef0] [c008f24c] vfs_read+0xb4/0x16c
 [c7b79f10] [c008f580] sys_read+0x4c/0x90
 [c7b79f40] [c0013a14] ret_from_syscall+0x0/0x38

It's OK to request the value of *any* GPIO; most GPIOs are bidirectional,
so configuring them as outputs just enables an output driver and doesn't
disable the input logic.

So the problem is that gpio_get_value_cansleep() isn't making the same
sanity check that gpio_get_value() does: making sure this GPIO isn't one
of the atypical "no input logic" cases.

Reported-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: <stable@kernel.org>		[2.6.27.x, 2.6.26.x, 2.6.25.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
David Brownell 2008-10-18 20:27:49 -07:00 committed by Linus Torvalds
parent e3274e9150
commit 978ccaa8ea
1 changed files with 1 additions and 1 deletions
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2
drivers/gpio/gpiolib.c
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@ -1105,7 +1105,7 @@ int gpio_get_value_cansleep(unsigned gpio)
might_sleep_if(extra_checks);
chip = gpio_to_chip(gpio);
return chip->get(chip, gpio - chip->base);
return chip->get ? chip->get(chip, gpio - chip->base) : 0;
}
EXPORT_SYMBOL_GPL(gpio_get_value_cansleep);