linux-kernel - Re: [RFC] cdc-acm: Fix potential deadlock (lockdep warning)

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Date:	Wed, 23 Nov 2011 20:55:57 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	Havard Skinnemoen <hskinnemoen@...gle.com>
CC:	Jiri Slaby <jirislaby@...il.com>, Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Alan Cox <alan@...ux.intel.com>
Subject: Re: [RFC] cdc-acm: Fix potential deadlock (lockdep warning)

On 11/23/2011 07:53 PM, Havard Skinnemoen wrote:
> --- a/drivers/usb/class/cdc-acm.c
> +++ b/drivers/usb/class/cdc-acm.c
...
> @@ -567,19 +574,10 @@ static void acm_tty_close(struct tty_struct *tty, struct file *filp)
>  
>  	/* Perform the closing process and see if we need to do the hardware
>  	   shutdown */
> -	if (!acm)
> -		return;
> -
> -	mutex_lock(&open_mutex);
>  	if (tty_port_close_start(&acm->port, tty, filp) == 0) {

Note that port->count is protected by port->lock usually. Till now it
used to be protected by open_mutex in your driver. As of now it is not
protected by anything. (Well, BTM is still there to save you, but...)

thanks,
-- 
js
suse labs
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