linux-kernel - Re: kernel oops

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Message-ID: <19f34abd0808180933r509b402i70fced0e1678d6fe@mail.gmail.com>
Date:	Mon, 18 Aug 2008 18:33:42 +0200
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	"Andrei Popa" <andrei.popa@...eo.ro>,
	"Oliver Neukum" <oneukum@...e.de>,
	"Greg Kroah-Hartman" <gregkh@...e.de>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: kernel oops

On Wed, Jul 23, 2008 at 7:11 PM, Vegard Nossum <vegard.nossum@...il.com> wrote:
> On Wed, Jul 23, 2008 at 2:52 PM, Andrei Popa <andrei.popa@...eo.ro> wrote:
>>
>> I installed gnokii-0.6.22-r2 and gave the command "gnokii --identify"
>> and the kernel oopsed:
>>
>> BUG: unable to handle kernel NULL pointer dereference at 00000458
>> IP: [<c0444b52>] mutex_unlock+0x0/0xb
>> *pde = 00000000
>> Oops: 0002 [#1] PREEMPT SMP
>>
>> Pid: 19043, comm: gnokii Not tainted (2.6.26-ineo7 #2)
>> EIP: 0060:[<c0444b52>] EFLAGS: 00010246 CPU: 0
>> EIP is at mutex_unlock+0x0/0xb
> ...
>>  [<c03830ae>] acm_tty_open+0x4c/0x214
>
> This shouldn't be too hard; the code is trying to unlock the mutex
> &acm->mutex even when "acm" is NULL. It seems that the label "err_out"
> is otherwise unused, so it makes sense to move this one step further
> down, so that it doesn't try to unlock the non-existent mutex.
>
> If the problem is reproducible, you could try the patch below!
>
>
> Vegard
>
> PS: I actually think the code has some other problems too. Shouldn't
> &acm->mutex be locked before we even inspect acm->dev?
>
>
> Reported-by: Andrei Popa <andrei.popa@...eo.ro>
> Signed-off-by: Vegard Nossum <vegard.nossum@...il.com>
>
> diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
> index 63c3404..74d03a7 100644
> --- a/drivers/usb/class/cdc-acm.c
> +++ b/drivers/usb/class/cdc-acm.c
> @@ -525,8 +525,8 @@ static int acm_tty_open(struct tty_struct *tty, struct file *filp)
>        tasklet_schedule(&acm->urb_task);
>
>  done:
> -err_out:
>        mutex_unlock(&acm->mutex);
> +err_out:
>        mutex_unlock(&open_mutex);
>        return rv;
>
>

Hi,

Latest -git seems to have the same problem, and this was about three
weeks ago, so.. Ping?


Vegard

-- 
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
	-- E. W. Dijkstra, EWD1036
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