Subject: Re: [PATCH net-next] net: reinstate rtnl in call_netdevice_notifiers()

From: [email-masked] (Eric W. Biederman)
Date: Thu, 23 Aug 2012 01:16:51 -0700

Eric Dumazet <[email-masked]> writes:

> From: Eric Dumazet <[email-masked]>
>
> Eric Biederman pointed out that not holding RTNL while calling
> call_netdevice_notifiers() was racy.
>
> This patch is a direct transcription his feedback
> against commit 0115e8e30d6fc (net: remove delay at device dismantle)
>
> Thanks Eric !

Looks good to me.

Acked-by: "Eric W. Biederman" <[email-masked]>

> Signed-off-by: Eric Dumazet <[email-masked]>
> Cc: Tom Herbert <[email-masked]>
> Cc: Mahesh Bandewar <[email-masked]>
> Cc: "Eric W. Biederman" <[email-masked]>
> Cc: Gao feng <[email-masked]>
> ---
> Note: After this patch, it seems less risky to push these fixes for 3.6,
> since notifiers have the guarantee that RTNL is held.
>
>  net/core/dev.c          |    9 +++++++--
>  net/core/fib_rules.c    |    3 +--
>  net/ipv4/devinet.c      |    6 +-----
>  net/ipv4/fib_frontend.c |    7 ++-----
>  net/ipv6/addrconf.c     |    6 +-----
>  5 files changed, 12 insertions(+), 19 deletions(-)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 0640d2a..bc857fe 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -1466,8 +1466,7 @@ EXPORT_SYMBOL(unregister_netdevice_notifier);
>  
>  int call_netdevice_notifiers(unsigned long val, struct net_device *dev)
>  {
> -	if (val != NETDEV_UNREGISTER_FINAL)
> -		ASSERT_RTNL();
> +	ASSERT_RTNL();
>  	return raw_notifier_call_chain(&netdev_chain, val, dev);
>  }
>  EXPORT_SYMBOL(call_netdevice_notifiers);
> @@ -5782,7 +5781,11 @@ static void netdev_wait_allrefs(struct net_device *dev)
>  
>  			/* Rebroadcast unregister notification */
>  			call_netdevice_notifiers(NETDEV_UNREGISTER, dev);
> +
> +			__rtnl_unlock();
>  			rcu_barrier();
> +			rtnl_lock();
> +
>  			call_netdevice_notifiers(NETDEV_UNREGISTER_FINAL, dev);
>  			if (test_bit(__LINK_STATE_LINKWATCH_PENDING,
>  				     &dev->state)) {
> @@ -5855,7 +5858,9 @@ void netdev_run_todo(void)
>  			= list_first_entry(&list, struct net_device, todo_list);
>  		list_del(&dev->todo_list);
>  
> +		rtnl_lock();
>  		call_netdevice_notifiers(NETDEV_UNREGISTER_FINAL, dev);
> +		__rtnl_unlock();
>  
>  		if (unlikely(dev->reg_state != NETREG_UNREGISTERING)) {
>  			pr_err("network todo '%s' but state %d\n",
> diff --git a/net/core/fib_rules.c b/net/core/fib_rules.c
> index 5850937..ab7db83 100644
> --- a/net/core/fib_rules.c
> +++ b/net/core/fib_rules.c
> @@ -711,16 +711,15 @@ static int fib_rules_event(struct notifier_block *this, unsigned long event,
>  	struct net *net = dev_net(dev);
>  	struct fib_rules_ops *ops;
>  
> +	ASSERT_RTNL();
>  
>  	switch (event) {
>  	case NETDEV_REGISTER:
> -		ASSERT_RTNL();
>  		list_for_each_entry(ops, &net->rules_ops, list)
>  			attach_rules(&ops->rules_list, dev);
>  		break;
>  
>  	case NETDEV_UNREGISTER:
> -		ASSERT_RTNL();
>  		list_for_each_entry(ops, &net->rules_ops, list)
>  			detach_rules(&ops->rules_list, dev);
>  		break;
> diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
> index 6a5e6e4..adf273f 100644
> --- a/net/ipv4/devinet.c
> +++ b/net/ipv4/devinet.c
> @@ -1147,12 +1147,8 @@ static int inetdev_event(struct notifier_block *this, unsigned long event,
>  			 void *ptr)
>  {
>  	struct net_device *dev = ptr;
> -	struct in_device *in_dev;
> -
> -	if (event == NETDEV_UNREGISTER_FINAL)
> -		goto out;
> +	struct in_device *in_dev = __in_dev_get_rtnl(dev);
>  
> -	in_dev = __in_dev_get_rtnl(dev);
>  	ASSERT_RTNL();
>  
>  	if (!in_dev) {
> diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
> index fd7d9ae..acdee32 100644
> --- a/net/ipv4/fib_frontend.c
> +++ b/net/ipv4/fib_frontend.c
> @@ -1050,9 +1050,6 @@ static int fib_netdev_event(struct notifier_block *this, unsigned long event, vo
>  		return NOTIFY_DONE;
>  	}
>  
> -	if (event == NETDEV_UNREGISTER_FINAL)
> -		return NOTIFY_DONE;
> -
>  	in_dev = __in_dev_get_rtnl(dev);
>  
>  	switch (event) {
> @@ -1064,14 +1061,14 @@ static int fib_netdev_event(struct notifier_block *this, unsigned long event, vo
>  		fib_sync_up(dev);
>  #endif
>  		atomic_inc(&net->ipv4.dev_addr_genid);
> -		rt_cache_flush(dev_net(dev), -1);
> +		rt_cache_flush(net, -1);
>  		break;
>  	case NETDEV_DOWN:
>  		fib_disable_ip(dev, 0, 0);
>  		break;
>  	case NETDEV_CHANGEMTU:
>  	case NETDEV_CHANGE:
> -		rt_cache_flush(dev_net(dev), 0);
> +		rt_cache_flush(net, 0);
>  		break;
>  	}
>  	return NOTIFY_DONE;
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index e581009..6bc85f7 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -2566,14 +2566,10 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
>  			   void *data)
>  {
>  	struct net_device *dev = (struct net_device *) data;
> -	struct inet6_dev *idev;
> +	struct inet6_dev *idev = __in6_dev_get(dev);
>  	int run_pending = 0;
>  	int err;
>  
> -	if (event == NETDEV_UNREGISTER_FINAL)
> -		return NOTIFY_DONE;
> -
> -	idev = __in6_dev_get(dev);
>  	switch (event) {
>  	case NETDEV_REGISTER:
>  		if (!idev && dev->mtu >= IPV6_MIN_MTU) {