USB: cdc-acm: don't unlock acm->mutex on error path

commit 74573ee7 upstream

On Wed, Jul 23, 2008 at 03:52:36PM +0300, Andrei Popa 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
>  [<c03830ae>] acm_tty_open+0x4c/0x214
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Tested-by: Andrei Popa <andrei.popa@i-neo.ro>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

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;