linux-kernel - Re: [PATCH] gpiolib: fix oops on reading sysfs exported GPIOs

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Message-Id: <200810160843.08553.david-b@pacbell.net>
Date:	Thu, 16 Oct 2008 08:43:08 -0700
From:	David Brownell <david-b@...bell.net>
To:	Anton Vorontsov <avorontsov@...mvista.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] gpiolib: fix oops on reading sysfs exported GPIOs

On Thursday 16 October 2008, Anton Vorontsov wrote:

> 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

Rude.  But notice it's not unique to the sysfs path.
Trying to fix only the sysfs path allows oosping in
other cases.


> GPIO users should always issue the gpio_direction_input() call and
> check its return value prior to trying gpio_get_value().

Not true; the API explicitly allows GPIOs to be treated
as bidirectional, even when they're configured as outputs.
That's because most GPIOs *are* bidirectional.

See the better patch in my next message.
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