[PATCH net-next] rds: tcp: remove register_netdevice_notifier infrastructure.

[PATCH net-next] rds: tcp: remove register_netdevice_notifier infrastructure.

[Sowmini Varadhan]

The netns deletion path does not need to wait for all net_devices
to be unregistered before dismantling rds_tcp state for the netns
(we are able to dismantle this state on module unload even when
all net_devices are active so there is no dependency here).

This patch removes code related to netdevice notifiers and
refactors all the code needed to dismantle rds_tcp state
into a ->exit callback for the pernet_operations used with
register_pernet_device().

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
---
 net/rds/tcp.c |   93 ++++++++++++++-------------------------------------------
 1 files changed, 23 insertions(+), 70 deletions(-)

diff --git a/net/rds/tcp.c b/net/rds/tcp.c
index 08ea9cd..4f3a32c 100644
--- a/net/rds/tcp.c
+++ b/net/rds/tcp.c
@@ -485,40 +485,6 @@ static __net_init int rds_tcp_init_net(struct net *net)
 	return err;
 }
 
-static void __net_exit rds_tcp_exit_net(struct net *net)
-{
-	struct rds_tcp_net *rtn = net_generic(net, rds_tcp_netid);
-
-	if (rtn->rds_tcp_sysctl)
-		unregister_net_sysctl_table(rtn->rds_tcp_sysctl);
-
-	if (net != &init_net && rtn->ctl_table)
-		kfree(rtn->ctl_table);
-
-	/* If rds_tcp_exit_net() is called as a result of netns deletion,
-	 * the rds_tcp_kill_sock() device notifier would already have cleaned
-	 * up the listen socket, thus there is no work to do in this function.
-	 *
-	 * If rds_tcp_exit_net() is called as a result of module unload,
-	 * i.e., due to rds_tcp_exit() -> unregister_pernet_subsys(), then
-	 * we do need to clean up the listen socket here.
-	 */
-	if (rtn->rds_tcp_listen_sock) {
-		struct socket *lsock = rtn->rds_tcp_listen_sock;
-
-		rtn->rds_tcp_listen_sock = NULL;
-		rds_tcp_listen_stop(lsock, &rtn->rds_tcp_accept_w);
-	}
-}
-
-static struct pernet_operations rds_tcp_net_ops = {
-	.init = rds_tcp_init_net,
-	.exit = rds_tcp_exit_net,
-	.id = &rds_tcp_netid,
-	.size = sizeof(struct rds_tcp_net),
-	.async = true,
-};
-
 static void rds_tcp_kill_sock(struct net *net)
 {
 	struct rds_tcp_connection *tc, *_tc;
@@ -546,40 +512,38 @@ static void rds_tcp_kill_sock(struct net *net)
 		rds_conn_destroy(tc->t_cpath->cp_conn);
 }
 
-void *rds_tcp_listen_sock_def_readable(struct net *net)
+static void __net_exit rds_tcp_exit_net(struct net *net)
 {
 	struct rds_tcp_net *rtn = net_generic(net, rds_tcp_netid);
-	struct socket *lsock = rtn->rds_tcp_listen_sock;
 
-	if (!lsock)
-		return NULL;
+	rds_tcp_kill_sock(net);
 
-	return lsock->sk->sk_user_data;
+	if (rtn->rds_tcp_sysctl)
+		unregister_net_sysctl_table(rtn->rds_tcp_sysctl);
+
+	if (net != &init_net && rtn->ctl_table)
+		kfree(rtn->ctl_table);
 }
 
-static int rds_tcp_dev_event(struct notifier_block *this,
-			     unsigned long event, void *ptr)
+static struct pernet_operations rds_tcp_net_ops = {
+	.init = rds_tcp_init_net,
+	.exit = rds_tcp_exit_net,
+	.id = &rds_tcp_netid,
+	.size = sizeof(struct rds_tcp_net),
+	.async = true,
+};
+
+void *rds_tcp_listen_sock_def_readable(struct net *net)
 {
-	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
+	struct rds_tcp_net *rtn = net_generic(net, rds_tcp_netid);
+	struct socket *lsock = rtn->rds_tcp_listen_sock;
 
-	/* rds-tcp registers as a pernet subys, so the ->exit will only
-	 * get invoked after network acitivity has quiesced. We need to
-	 * clean up all sockets  to quiesce network activity, and use
-	 * the unregistration of the per-net loopback device as a trigger
-	 * to start that cleanup.
-	 */
-	if (event == NETDEV_UNREGISTER_FINAL &&
-	    dev->ifindex == LOOPBACK_IFINDEX)
-		rds_tcp_kill_sock(dev_net(dev));
+	if (!lsock)
+		return NULL;
 
-	return NOTIFY_DONE;
+	return lsock->sk->sk_user_data;
 }
 
-static struct notifier_block rds_tcp_dev_notifier = {
-	.notifier_call        = rds_tcp_dev_event,
-	.priority = -10, /* must be called after other network notifiers */
-};
-
 /* when sysctl is used to modify some kernel socket parameters,this
  * function  resets the RDS connections in that netns  so that we can
  * restart with new parameters.  The assumption is that such reset
@@ -625,9 +589,7 @@ static void rds_tcp_exit(void)
 	rds_tcp_set_unloading();
 	synchronize_rcu();
 	rds_info_deregister_func(RDS_INFO_TCP_SOCKETS, rds_tcp_tc_info);
-	unregister_pernet_subsys(&rds_tcp_net_ops);
-	if (unregister_netdevice_notifier(&rds_tcp_dev_notifier))
-		pr_warn("could not unregister rds_tcp_dev_notifier\n");
+	unregister_pernet_device(&rds_tcp_net_ops);
 	rds_tcp_destroy_conns();
 	rds_trans_unregister(&rds_tcp_transport);
 	rds_tcp_recv_exit();
@@ -651,24 +613,15 @@ static int rds_tcp_init(void)
 	if (ret)
 		goto out_slab;
 
-	ret = register_pernet_subsys(&rds_tcp_net_ops);
+	ret = register_pernet_device(&rds_tcp_net_ops);
 	if (ret)
 		goto out_recv;
 
-	ret = register_netdevice_notifier(&rds_tcp_dev_notifier);
-	if (ret) {
-		pr_warn("could not register rds_tcp_dev_notifier\n");
-		goto out_pernet;
-	}
-
 	rds_trans_register(&rds_tcp_transport);
 
 	rds_info_register_func(RDS_INFO_TCP_SOCKETS, rds_tcp_tc_info);
 
 	goto out;
-
-out_pernet:
-	unregister_pernet_subsys(&rds_tcp_net_ops);
 out_recv:
 	rds_tcp_recv_exit();
 out_slab:
-- 
1.7.1

Re: [PATCH net-next] rds: tcp: remove register_netdevice_notifier infrastructure.

[Kirill Tkhai]

On 19.03.2018 16:52, Sowmini Varadhan wrote:
> The netns deletion path does not need to wait for all net_devices
> to be unregistered before dismantling rds_tcp state for the netns
> (we are able to dismantle this state on module unload even when
> all net_devices are active so there is no dependency here).
> 
> This patch removes code related to netdevice notifiers and
> refactors all the code needed to dismantle rds_tcp state
> into a ->exit callback for the pernet_operations used with
> register_pernet_device().
> 
> Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>

I just repeat my words:
rds_tcp_listen_sock destruction looks nice and safe, since all
the places the sockets is dereferenced use sk_callback_lock.
So they don't miss rds_tcp_listen_sock = NULL, as rds_tcp_listen_stop()
takes the lock too.

rds_tcp_conn_list is populated from:

1)rds_tcp_accept_one(), which can't happen after we flushed the queue
in rds_tcp_listen_stop();

2)rds_sendmsg(), which is triggered by userspace, and that's impossible,
when net is dead;

3)rds_ib_cm_handle_connect(), which call rds_conn_create() with init_net
argument only. This may race with module unloading only, but this problem
is already solved in RDS by rds_destroy_pending() check, which care about
that.

Reviewed-by: Kirill Tkhai <ktkhai@virtuozzo.com>

(The only thing I don't know is the reason we need to destroy the sockets
 before last netdevice, but I haven't dived into that. Just to mention this...).

Thanks, Sowmini.

Kirill

> ---
>  net/rds/tcp.c |   93 ++++++++++++++-------------------------------------------
>  1 files changed, 23 insertions(+), 70 deletions(-)
> 
> diff --git a/net/rds/tcp.c b/net/rds/tcp.c
> index 08ea9cd..4f3a32c 100644
> --- a/net/rds/tcp.c
> +++ b/net/rds/tcp.c
> @@ -485,40 +485,6 @@ static __net_init int rds_tcp_init_net(struct net *net)
>  	return err;
>  }
>  
> -static void __net_exit rds_tcp_exit_net(struct net *net)
> -{
> -	struct rds_tcp_net *rtn = net_generic(net, rds_tcp_netid);
> -
> -	if (rtn->rds_tcp_sysctl)
> -		unregister_net_sysctl_table(rtn->rds_tcp_sysctl);
> -
> -	if (net != &init_net && rtn->ctl_table)
> -		kfree(rtn->ctl_table);
> -
> -	/* If rds_tcp_exit_net() is called as a result of netns deletion,
> -	 * the rds_tcp_kill_sock() device notifier would already have cleaned
> -	 * up the listen socket, thus there is no work to do in this function.
> -	 *
> -	 * If rds_tcp_exit_net() is called as a result of module unload,
> -	 * i.e., due to rds_tcp_exit() -> unregister_pernet_subsys(), then
> -	 * we do need to clean up the listen socket here.
> -	 */
> -	if (rtn->rds_tcp_listen_sock) {
> -		struct socket *lsock = rtn->rds_tcp_listen_sock;
> -
> -		rtn->rds_tcp_listen_sock = NULL;
> -		rds_tcp_listen_stop(lsock, &rtn->rds_tcp_accept_w);
> -	}
> -}
> -
> -static struct pernet_operations rds_tcp_net_ops = {
> -	.init = rds_tcp_init_net,
> -	.exit = rds_tcp_exit_net,
> -	.id = &rds_tcp_netid,
> -	.size = sizeof(struct rds_tcp_net),
> -	.async = true,
> -};
> -
>  static void rds_tcp_kill_sock(struct net *net)
>  {
>  	struct rds_tcp_connection *tc, *_tc;
> @@ -546,40 +512,38 @@ static void rds_tcp_kill_sock(struct net *net)
>  		rds_conn_destroy(tc->t_cpath->cp_conn);
>  }
>  
> -void *rds_tcp_listen_sock_def_readable(struct net *net)
> +static void __net_exit rds_tcp_exit_net(struct net *net)
>  {
>  	struct rds_tcp_net *rtn = net_generic(net, rds_tcp_netid);
> -	struct socket *lsock = rtn->rds_tcp_listen_sock;
>  
> -	if (!lsock)
> -		return NULL;
> +	rds_tcp_kill_sock(net);
>  
> -	return lsock->sk->sk_user_data;
> +	if (rtn->rds_tcp_sysctl)
> +		unregister_net_sysctl_table(rtn->rds_tcp_sysctl);
> +
> +	if (net != &init_net && rtn->ctl_table)
> +		kfree(rtn->ctl_table);
>  }
>  
> -static int rds_tcp_dev_event(struct notifier_block *this,
> -			     unsigned long event, void *ptr)
> +static struct pernet_operations rds_tcp_net_ops = {
> +	.init = rds_tcp_init_net,
> +	.exit = rds_tcp_exit_net,
> +	.id = &rds_tcp_netid,
> +	.size = sizeof(struct rds_tcp_net),
> +	.async = true,
> +};
> +
> +void *rds_tcp_listen_sock_def_readable(struct net *net)
>  {
> -	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
> +	struct rds_tcp_net *rtn = net_generic(net, rds_tcp_netid);
> +	struct socket *lsock = rtn->rds_tcp_listen_sock;
>  
> -	/* rds-tcp registers as a pernet subys, so the ->exit will only
> -	 * get invoked after network acitivity has quiesced. We need to
> -	 * clean up all sockets  to quiesce network activity, and use
> -	 * the unregistration of the per-net loopback device as a trigger
> -	 * to start that cleanup.
> -	 */
> -	if (event == NETDEV_UNREGISTER_FINAL &&
> -	    dev->ifindex == LOOPBACK_IFINDEX)
> -		rds_tcp_kill_sock(dev_net(dev));
> +	if (!lsock)
> +		return NULL;
>  
> -	return NOTIFY_DONE;
> +	return lsock->sk->sk_user_data;
>  }
>  
> -static struct notifier_block rds_tcp_dev_notifier = {
> -	.notifier_call        = rds_tcp_dev_event,
> -	.priority = -10, /* must be called after other network notifiers */
> -};
> -
>  /* when sysctl is used to modify some kernel socket parameters,this
>   * function  resets the RDS connections in that netns  so that we can
>   * restart with new parameters.  The assumption is that such reset
> @@ -625,9 +589,7 @@ static void rds_tcp_exit(void)
>  	rds_tcp_set_unloading();
>  	synchronize_rcu();
>  	rds_info_deregister_func(RDS_INFO_TCP_SOCKETS, rds_tcp_tc_info);
> -	unregister_pernet_subsys(&rds_tcp_net_ops);
> -	if (unregister_netdevice_notifier(&rds_tcp_dev_notifier))
> -		pr_warn("could not unregister rds_tcp_dev_notifier\n");
> +	unregister_pernet_device(&rds_tcp_net_ops);
>  	rds_tcp_destroy_conns();
>  	rds_trans_unregister(&rds_tcp_transport);
>  	rds_tcp_recv_exit();
> @@ -651,24 +613,15 @@ static int rds_tcp_init(void)
>  	if (ret)
>  		goto out_slab;
>  
> -	ret = register_pernet_subsys(&rds_tcp_net_ops);
> +	ret = register_pernet_device(&rds_tcp_net_ops);
>  	if (ret)
>  		goto out_recv;
>  
> -	ret = register_netdevice_notifier(&rds_tcp_dev_notifier);
> -	if (ret) {
> -		pr_warn("could not register rds_tcp_dev_notifier\n");
> -		goto out_pernet;
> -	}
> -
>  	rds_trans_register(&rds_tcp_transport);
>  
>  	rds_info_register_func(RDS_INFO_TCP_SOCKETS, rds_tcp_tc_info);
>  
>  	goto out;
> -
> -out_pernet:
> -	unregister_pernet_subsys(&rds_tcp_net_ops);
>  out_recv:
>  	rds_tcp_recv_exit();
>  out_slab:
> 

Re: [PATCH net-next] rds: tcp: remove register_netdevice_notifier infrastructure.

[David Miller]

From: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Date: Mon, 19 Mar 2018 06:52:48 -0700

> The netns deletion path does not need to wait for all net_devices
> to be unregistered before dismantling rds_tcp state for the netns
> (we are able to dismantle this state on module unload even when
> all net_devices are active so there is no dependency here).
> 
> This patch removes code related to netdevice notifiers and
> refactors all the code needed to dismantle rds_tcp state
> into a ->exit callback for the pernet_operations used with
> register_pernet_device().
> 
> Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>

Applied.