Date:   Mon, 19 Mar 2018 13:08:42 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     Sowmini Varadhan <sowmini.varadhan@...cle.com>
Cc:     rds-devel@....oracle.com, linux-rdma@...r.kernel.org,
        netdev@...r.kernel.org, edumazet@...gle.com, davem@...emloft.net
Subject: Re: [rds-devel] [PATCH RFC RFC] rds: Use NETDEV_UNREGISTER in
 rds_tcp_dev_event() (then kill NETDEV_UNREGISTER_FINAL)

Hi, Sowmini,

thanks for looking into this.

On 18.03.2018 23:45, Sowmini Varadhan wrote:
> On (03/18/18 00:55), Kirill Tkhai wrote:
>>
>> I just want to make rds not using NETDEV_UNREGISTER_FINAL. If there is
>> another solution to do that, I'm not again that.
> 
> The patch below takes care of this. I've done some preliminary testing,
> and I'll send it upstream after doing additional self-review/testing.
> Please also take a look, if you can, to see if I missed something.
> 
> Thanks for the input,
> 
> --Sowmini
> -------------------------------patch follows--------------------------------
> 
> diff --git a/net/rds/tcp.c b/net/rds/tcp.c
> index 08ea9cd..87c2643 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);

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:

static bool rds_tcp_is_unloading(struct rds_connection *conn)
{
        return atomic_read(&rds_tcp_unloading) != 0;
}

static void rds_tcp_exit(void)
{
        rds_tcp_set_unloading();
        synchronize_rcu();
 	...
}

static struct rds_connection * __rds_conn_create(...)
{
	...
        rcu_read_lock();
        if (rds_destroy_pending(conn))
                ret = -ENETDOWN;
        else    
                ret = trans->conn_alloc(conn, GFP_ATOMIC);
	...
}

So, everything looks good for me.

Kirill

>  
> -	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 +613,17 @@ 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);
> +	unregister_pernet_device(&rds_tcp_net_ops);
>  out_recv:
>  	rds_tcp_recv_exit();
>  out_slab:

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