Re: [Patch] net: kill an RCU warning in inet_fill_link_af()

[Eric Dumazet <eric.dumazet@gmail.com>]

Le mercredi 01 décembre 2010 à 19:14 +0800, Amerigo Wang a écrit :
> From: WANG Cong <amwang@redhat.com>
> 
> The latest net-next-2.6 triggers an RCU warning during boot,
> lockdep complains that in inet_fill_link_af() we call rcu_dereference_check()
> without rcu_read_lock() protection.
> 
> This patch fixes it by replacing __in_dev_get_rcu() with in_dev_get().
> 
> Signed-off-by: WANG Cong <amwang@redhat.com>
> 

Sorry patch is not the right fix. Please take a look at commit 95ae6b22

We are working hard to remove all the not needed get()/put(), not to add
new ones ;)


> ---
> diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
> index d9f71ba..73baed8 100644
> --- a/net/ipv4/devinet.c
> +++ b/net/ipv4/devinet.c
> @@ -1258,31 +1258,36 @@ errout:
>  
>  static size_t inet_get_link_af_size(const struct net_device *dev)
>  {
> -	struct in_device *in_dev = __in_dev_get_rcu(dev);
> +	struct in_device *in_dev = in_dev_get(dev);
>  
>  	if (!in_dev)
>  		return 0;
>  
> +	in_dev_put(in_dev);
>  	return nla_total_size(IPV4_DEVCONF_MAX * 4); /* IFLA_INET_CONF */
>  }
>  

In this function why should we even take a reference, just to check if
pointer exists ?

If RTNL is held (I believe so), just use __in_dev_get_rtnl()

>  static int inet_fill_link_af(struct sk_buff *skb, const struct net_device *dev)
>  {
> -	struct in_device *in_dev = __in_dev_get_rcu(dev);
> +	struct in_device *in_dev = in_dev_get(dev);
>  	struct nlattr *nla;
> -	int i;
> +	int i, ret = 0;
>  
>  	if (!in_dev)
>  		return -ENODATA;
>  
>  	nla = nla_reserve(skb, IFLA_INET_CONF, IPV4_DEVCONF_MAX * 4);
> -	if (nla == NULL)
> -		return -EMSGSIZE;
> +	if (nla == NULL) {
> +		ret = -EMSGSIZE;
> +		goto out;
> +	}
>  
>  	for (i = 0; i < IPV4_DEVCONF_MAX; i++)
>  		((u32 *) nla_data(nla))[i] = in_dev->cnf.data[i];
>  
> -	return 0;
> +out:
> +	in_dev_put(in_dev);
> +	return ret;
>  }


In this function we hold RTNL...
 Please use __in_dev_get_rtnl()


>  
>  static const struct nla_policy inet_af_policy[IFLA_INET_MAX+1] = {
> @@ -1293,11 +1298,14 @@ static int inet_validate_link_af(const struct net_device *dev,
>  				 const struct nlattr *nla)
>  {
>  	struct nlattr *a, *tb[IFLA_INET_MAX+1];
> +	struct in_device *in_dev = in_dev_get(dev);
>  	int err, rem;
>  
> -	if (dev && !__in_dev_get_rcu(dev))
> +	if (dev && !in_dev)
>  		return -EAFNOSUPPORT;
>  
> +	in_dev_put(in_dev);
> +
>  	err = nla_parse_nested(tb, IFLA_INET_MAX, nla, inet_af_policy);
>  	if (err < 0)
>  		return err;
> @@ -1319,7 +1327,7 @@ static int inet_validate_link_af(const struct net_device *dev,
>  
>  static int inet_set_link_af(struct net_device *dev, const struct nlattr *nla)
>  {
> -	struct in_device *in_dev = __in_dev_get_rcu(dev);
> +	struct in_device *in_dev = in_dev_get(dev);
>  	struct nlattr *a, *tb[IFLA_INET_MAX+1];
>  	int rem;
>  
> @@ -1334,6 +1342,7 @@ static int inet_set_link_af(struct net_device *dev, const struct nlattr *nla)
>  			ipv4_devconf_set(in_dev, nla_type(a), nla_get_u32(a));
>  	}
>  
> +	in_dev_put(in_dev);
>  	return 0;
>  }

Same here. RTNL is held. Please use __in_dev_get_rtnl()