linux-kernel - Re: [PATCH] fix oops in usbserial

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Date:	Fri, 15 Oct 2010 10:15:34 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	m00150988@...wei.com
cc:	USB list <linux-usb@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	<zihan@...wei.com>, Lin Lei <Lin.Lei@...wei.com>,
	Franko Fang <huananhu@...wei.com>, <wangyeqi@...wei.com>
Subject: Re: [PATCH] fix oops in usbserial_cleanup function;

On Fri, 15 Oct 2010 m00150988@...wei.com wrote:

> From:ma rui <m00150988@...wei.com>
> 1. I find this bug on OpenSUSE 11.3 which kernel version is 2.6.34, but the latest kernel version 2.6.36-rc7 aslo have this bug. This patch is based on
> the kernel of 2.6.36-rc7
> 2. bug report:
>    a. Install huawei datacard dashboard on OpenSUSE 11.3
>    b. Plug in huawei datacard into OpenSUSE 11.3 which kernel version is 2.6.36-rc7
>    c. After the dashboard has detected the device, I pull out the usb datacard
>    d. Close dashboard,then kernel panic will happen in usbserial_clean function
> 
> Yes, the datacard exit without close the port. 
> 
> But after the dashboard connect internet with hauwei datacard, then Hibernate/resume, the bug will happen too.
> Do you have any other good idea to resolve this bug,or please apply my patch,thanks. :)
> 
> 
> Signed-off-by: ma rui <m00150988@...wei.com>
> 
> 
> diff -uprN -X linux-2.6.36-rc7_orig/Documentation/dontdiff linux-2.6.36-rc7_orig/drivers/usb/serial/usb-serial.c linux-2.6.36-rc7/drivers/usb/serial/usb-serial.c
> --- linux-2.6.36-rc7_orig/drivers/usb/serial/usb-serial.c	2010-10-06 16:39:52.000000000 -0400
> +++ linux-2.6.36-rc7/drivers/usb/serial/usb-serial.c	2010-10-15 01:57:36.000000000 -0400
> @@ -328,6 +328,16 @@ static void serial_cleanup(struct tty_st
>  	/* The console is magical.  Do not hang up the console hardware
>  	 * or there will be tears.
>  	 */
> +	if (NULL == port)
> +		return;
> +	mutex_lock(&port->serial->disc_mutex);
> +	if (port->serial->disconnected) {
> +		return_serial(port->serial);
> +		mutex_unlock(&port->serial->disc_mutex);
> +		return;
> +	}
> +	mutex_unlock(&port->serial->disc_mutex);
> +
>  	if (port->port.console)
>  		return;

This patch is clearly wrong, since it skips some of the actions that 
should be taken by serial_cleanup even if the port is already 
disconnected.

Besides, the main point of the patch is to avoid problems when 
port = tty->driver_data turns out to be NULL.  But the only place where 
tty->driver_data is set to NULL is further below in this same function!  
So the problems should never arise.

If they do arise, it indicates there's a bug somewhere else.  That 
other bug can't be fixed by changing this function.

Alan Stern

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