From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner+w=401wt.eu-S1759370AbZEMKKg@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1759370AbZEMKKg (ORCPT <rfc822;w@1wt.eu>);
	Wed, 13 May 2009 06:10:36 -0400
Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759266AbZEMKKV
	(ORCPT <rfc822;linux-kernel-outgoing>);
	Wed, 13 May 2009 06:10:21 -0400
Received: from mxout1.volkswagen.de ([194.114.62.41]:17057 "EHLO
	mxout1.volkswagen.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1757922AbZEMKKU (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Wed, 13 May 2009 06:10:20 -0400
X-Greylist: delayed 390 seconds by postgrey-1.27 at vger.kernel.org; Wed, 13 May 2009 06:10:19 EDT
Message-ID: <4A0A9AC1.2090603@volkswagen.de>
Date: Wed, 13 May 2009 12:02:41 +0200
From: Oliver Hartkopp <oliver.hartkopp@volkswagen.de>
User-Agent: Thunderbird 2.0.0.21 (Windows/20090302)
MIME-Version: 1.0
To: Andrew Morton <akpm@linux-foundation.org>,
       Wolfgang Grandegger <wg@grandegger.com>
CC: netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 3/7] [PATCH 3/8] can: CAN Network device driver and
 Netlink interface
References: <20090512092757.048938233@denx.de><20090512092757.574693100@denx.de> <20090512233052.ecd600f1.akpm@linux-foundation.org>
In-Reply-To: <20090512233052.ecd600f1.akpm@linux-foundation.org>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
X-OriginalArrivalTime: 13 May 2009 10:02:28.0098 (UTC) FILETIME=[EC204620:01C9D3B1]
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Andrew Morton wrote:
> On Tue, 12 May 2009 11:28:00 +0200 Wolfgang Grandegger <wg@grandegger.com> wrote:
>
>   
>> +int can_restart_now(struct net_device *dev)
>> +{
>> +	struct can_priv *priv = netdev_priv(dev);
>> +	struct net_device_stats *stats = &dev->stats;
>> +	struct sk_buff *skb;
>> +	struct can_frame *cf;
>> +	int err;
>> +
>> +	/* Synchronize with dev->hard_start_xmit() */
>> +	netif_tx_lock(dev);
>> +
>> +	/* Ensure that no more messages can go out */
>> +	if (netif_carrier_ok(dev))
>> +		netif_carrier_off(dev);
>> +
>> +	/* Ensure that no more messages can come in */
>> +	err = priv->do_set_mode(dev, CAN_MODE_STOP);
>> +	if (err)
>> +		return err;
>> +
>> +	/*  Now it's save to clean up */
>> +	del_timer_sync(&priv->restart_timer);
>>     
>
> This is deadlockable.
>
> It calls del_timer_sync() while holding netif_tx_lock().  But the timer
> handler (can_restart_now()) also takes netif_tx_lock().  So if the
> timer handler is presently running, it's sitting there spinning in
> netif_tx_lock().  And del_timer_sync() is sitting there waiting for the
> timer handler to complete.
>
>
>   

Hi Wolfgang,

would it be an appropriate solution, just to invoke

netif_stop_queue() in can_bus_off()

and invoke

netif_wake_queue() in can_restart_now()

???

In a BUSOFF condition we're not able to send CAN frames anyway, so  we 
can disable the device queue and the we won't  need any netif_tx_lock() 
right?

AFAIK this was the original implementation before some of the latest 
improvement with the netif_carrier stuff.

What do you think?

Best regards,
Oliver