linux-kernel - Re: [BUG] 2.6.38-rc2: Circular Locking Dependency

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Date:	Wed, 09 Feb 2011 08:26:37 +0100
From:	Knut Petersen <Knut_Petersen@...nline.de>
To:	David Miller <davem@...emloft.net>
CC:	paulus@...ba.org, linux-kernel@...r.kernel.org,
	mostrows@...thlink.net, linux-ppp@...r.kernel.org,
	xiaosuo@...il.com, eric.dumazet@...il.com, ebiederm@...ssion.com
Subject: Re: [BUG] 2.6.38-rc2: Circular Locking Dependency

Am 09.02.2011 00:04, schrieb David Miller:
> From: David Miller <davem@...emloft.net>
> Date: Tue, 08 Feb 2011 00:07:21 -0800 (PST)
>
> [ Eric B., CC:'ing you so that you are aware of the init network
>   namespace leak that's fixed as a side effect of this change. ]
>
>   
>> From: Knut Petersen <Knut_Petersen@...nline.de>
>> Date: Tue, 08 Feb 2011 08:51:22 +0100
>>
>>     
>>> I bisected the problem with the following result:
>>>
>>> aa9421041128abb4d269ee1dc502ff65fb3b7d69 is the first bad commit
>>> commit aa9421041128abb4d269ee1dc502ff65fb3b7d69
>>> Author: Changli Gao <xiaosuo@...il.com>
>>> Date:   Sat Dec 4 02:31:41 2010 +0000
>>>
>>>     net: init ingress queue
>>>
>>>     The dev field of ingress queue is forgot to initialized, then NULL
>>>     pointer dereference happens in qdisc_alloc().
>>>
>>>     Move inits of tx queues to netif_alloc_netdev_queues().
>>>
>>>     Signed-off-by: Changli Gao <xiaosuo@...il.com>
>>>     Acked-by: Eric Dumazet <eric.dumazet@...il.com>
>>>     Signed-off-by: David S. Miller <davem@...emloft.net>
>>>
>>> :040000 040000 dcbb6ab41c4308cba1bc6823d200dcf92aa402d8
>>> b5e190ec681d26ffe62d1d0214c4ef77b8034189 M      net
>>>       
>> Indeed, this initialization is now too early for the sake
>> of getting the lockdep bits right.  The problem is that at
>> the point in which we call netif_alloc_netdev_queue() we
>> haven't initialized dev->type yet, it is therefore always
>> zero when we setup the lockdep class for ->_xmit_lock.
>>     
> Ok, this should fix it, please test it out for me.
>
> Thanks!
>   

Yes, that patch does solve the problem, and I do not see
any negative effects.

Thanks!

Knut

> --------------------
> net: Fix lockdep regression caused by initializing netdev queues too early.
>
> In commit aa9421041128abb4d269ee1dc502ff65fb3b7d69 ("net: init ingress
> queue") we moved the allocation and lock initialization of the queues
> into alloc_netdev_mq() since register_netdevice() is way too late.
>
> The problem is that dev->type is not setup until the setup()
> callback is invoked by alloc_netdev_mq(), and the dev->type is
> what determines the lockdep class to use for the locks in the
> queues.
>
> Fix this by doing the queue allocation after the setup() callback
> runs.
>
> This is safe because the setup() callback is not allowed to make any
> state changes that need to be undone on error (memory allocations,
> etc.).  It may, however, make state changes that are undone by
> free_netdev() (such as netif_napi_add(), which is done by the
> ipoib driver's setup routine).
>
> The previous code also leaked a reference to the &init_net namespace
> object on RX/TX queue allocation failures.
>
> Signed-off-by: David S. Miller <davem@...emloft.net>
> ---
>  net/core/dev.c |   27 ++++++++++++++++-----------
>  1 files changed, 16 insertions(+), 11 deletions(-)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index b6d0bf8..8e726cb 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -5660,30 +5660,35 @@ struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name,
>  
>  	dev_net_set(dev, &init_net);
>  
> +	dev->gso_max_size = GSO_MAX_SIZE;
> +
> +	INIT_LIST_HEAD(&dev->ethtool_ntuple_list.list);
> +	dev->ethtool_ntuple_list.count = 0;
> +	INIT_LIST_HEAD(&dev->napi_list);
> +	INIT_LIST_HEAD(&dev->unreg_list);
> +	INIT_LIST_HEAD(&dev->link_watch_list);
> +	dev->priv_flags = IFF_XMIT_DST_RELEASE;
> +	setup(dev);
> +
>  	dev->num_tx_queues = txqs;
>  	dev->real_num_tx_queues = txqs;
>  	if (netif_alloc_netdev_queues(dev))
> -		goto free_pcpu;
> +		goto free_all;
>  
>  #ifdef CONFIG_RPS
>  	dev->num_rx_queues = rxqs;
>  	dev->real_num_rx_queues = rxqs;
>  	if (netif_alloc_rx_queues(dev))
> -		goto free_pcpu;
> +		goto free_all;
>  #endif
>  
> -	dev->gso_max_size = GSO_MAX_SIZE;
> -
> -	INIT_LIST_HEAD(&dev->ethtool_ntuple_list.list);
> -	dev->ethtool_ntuple_list.count = 0;
> -	INIT_LIST_HEAD(&dev->napi_list);
> -	INIT_LIST_HEAD(&dev->unreg_list);
> -	INIT_LIST_HEAD(&dev->link_watch_list);
> -	dev->priv_flags = IFF_XMIT_DST_RELEASE;
> -	setup(dev);
>  	strcpy(dev->name, name);
>  	return dev;
>  
> +free_all:
> +	free_netdev(dev);
> +	return NULL;
> +
>  free_pcpu:
>  	free_percpu(dev->pcpu_refcnt);
>  	kfree(dev->_tx);
>   

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