Re: [PATCH net-next v3 1/2] RDS: TCP: Add sysctl tunables for sndbuf/rcvbuf on rds-tcp socket

Add per-net sysctl tunables to set the size of sndbuf and
rcvbuf on the kernel tcp socket.

The tunables are added at /proc/sys/net/rds/tcp/rds_tcp_sndbuf
and /proc/sys/net/rds/tcp/rds_tcp_rcvbuf.

Since these values must be set before accept() or connect(),
and there may be an arbitrary number of existing rds-tcp
sockets when the tunable is modified. To make sure that all
connections in the netns pick up the same value for the tunable,
we reset existing rds-tcp connections in the netns, so that
they can reconnect with the new parameters.

Signed-off-by: Sowmini Varadhan <redacted>
---
v2; use sysctl instead of module param. Tunabes are now per netns,
     and can be dynamically modified without restarting all namespaces.
v3: review comments from Santosh Shilimkar,  Eric Dumazet

  net/rds/tcp.c |  143 +++++++++++++++++++++++++++++++++++++++++++++++++++++----
  1 files changed, 134 insertions(+), 9 deletions(-)

diff --git a/net/rds/tcp.c b/net/rds/tcp.c
index ad60299..b720b25 100644
--- a/net/rds/tcp.c
+++ b/net/rds/tcp.c

@@ -54,6 +54,28 @@ static struct kmem_cache *rds_tcp_conn_slab;

  #define RDS_TCP_DEFAULT_BUFSIZE (128 * 1024)

+static int sndbuf_handler(struct ctl_table *ctl, int write,
+			  void __user *buffer, size_t *lenp, loff_t *fpos);
+static int rcvbuf_handler(struct ctl_table *ctl, int write,
+			  void __user *buffer, size_t *lenp, loff_t *fpos);
+static struct ctl_table rds_tcp_sysctl_table[] = {
+	{
+		.procname       = "rds_tcp_sndbuf",
+		/* data is per-net pointer */
+		.maxlen         = sizeof(int),
+		.mode           = 0644,
+		.proc_handler   = sndbuf_handler,
+	},
+	{
+		.procname       = "rds_tcp_rcvbuf",
+		/* data is per-net pointer */
+		.maxlen         = sizeof(int),
+		.mode           = 0644,
+		.proc_handler   = rcvbuf_handler,
+	},
+	{ }
+};

  /* doing it this way avoids calling tcp_sk() */
  void rds_tcp_nonagle(struct socket *sock)
  {

@@ -66,15 +88,6 @@ void rds_tcp_nonagle(struct socket *sock)
  	set_fs(oldfs);
  }

-/* All module specific customizations to the RDS-TCP socket should be done in
- * rds_tcp_tune() and applied after socket creation. In general these
- * customizations should be tunable via module_param()
- */
-void rds_tcp_tune(struct socket *sock)
-{
-	rds_tcp_nonagle(sock);
-}
-
  u32 rds_tcp_snd_nxt(struct rds_tcp_connection *tc)
  {
  	return tcp_sk(tc->t_sock->sk)->snd_nxt;

@@ -272,8 +285,33 @@ static int rds_tcp_netid;
  struct rds_tcp_net {
  	struct socket *rds_tcp_listen_sock;
  	struct work_struct rds_tcp_accept_w;
+	struct ctl_table_header *rds_tcp_sysctl;
+	int sndbuf_size;
+	int rcvbuf_size;
  };

+/* All module specific customizations to the RDS-TCP socket should be done in
+ * rds_tcp_tune() and applied after socket creation.
+ */
+void rds_tcp_tune(struct socket *sock)
+{
+	struct sock *sk = sock->sk;
+	struct net *net = sock_net(sk);
+	struct rds_tcp_net *rtn = net_generic(net, rds_tcp_netid);
+
+	rds_tcp_nonagle(sock);
+	lock_sock(sk);
+	if (rtn->sndbuf_size > 0) {
+		sk->sk_sndbuf = rtn->sndbuf_size;
+		sk->sk_userlocks |= SOCK_SNDBUF_LOCK;
+	}
+	if (rtn->rcvbuf_size > 0) {
+		sk->sk_sndbuf = rtn->rcvbuf_size;
+		sk->sk_userlocks |= SOCK_RCVBUF_LOCK;
+	}
+	release_sock(sk);
+}
+
  static void rds_tcp_accept_worker(struct work_struct *work)
  {
  	struct rds_tcp_net *rtn = container_of(work,

@@ -296,9 +334,17 @@ static __net_init int rds_tcp_init_net(struct net *net)
  {
  	struct rds_tcp_net *rtn = net_generic(net, rds_tcp_netid);

+	/* 0 value for {snd, rcv}buf_size implies we let the stack
+	 * pick the default, and permit auto-tuning of buffer size.
+	 */
+	rtn->sndbuf_size = 0;
+	rtn->rcvbuf_size = 0;
+	rtn->rds_tcp_sysctl = register_net_sysctl(net, "net/rds/tcp",
+						  rds_tcp_sysctl_table);

  	rtn->rds_tcp_listen_sock = rds_tcp_listen_init(net);
  	if (!rtn->rds_tcp_listen_sock) {
  		pr_warn("could not set up listen sock\n");
+		unregister_net_sysctl_table(rtn->rds_tcp_sysctl);
  		return -EAFNOSUPPORT;
  	}
  	INIT_WORK(&rtn->rds_tcp_accept_w, rds_tcp_accept_worker);

@@ -309,6 +355,7 @@ static void __net_exit rds_tcp_exit_net(struct net *net)
  {
  	struct rds_tcp_net *rtn = net_generic(net, rds_tcp_netid);

+	unregister_net_sysctl_table(rtn->rds_tcp_sysctl);
  	/* 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.

@@ -383,6 +430,84 @@ static struct notifier_block rds_tcp_dev_notifier = {
  	.priority = -10, /* must be called after other network notifiers */
  };

+static int user_atoi(char __user *ubuf, size_t len)
+{
+	char buf[16];
+	unsigned long ret;
+	int err;
+
+	if (len > 15)
+		return -EINVAL;
+
+	if (copy_from_user(buf, ubuf, len))
+		return -EFAULT;
+
+	buf[len] = 0;
+	err =  kstrtoul(buf, 0, &ret);
+	if (err != 0)
+		return -ERANGE;
+	return  ret;
+}
+
+/* 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
+ * events are few and far-between.
+ */
+static void rds_tcp_sysctl_reset(struct net *net)
+{
+	struct rds_tcp_connection *tc, *_tc;
+
+	spin_lock_irq(&rds_tcp_conn_lock);
+	list_for_each_entry_safe(tc, _tc, &rds_tcp_conn_list, t_tcp_node) {
+		struct net *c_net = read_pnet(&tc->conn->c_net);
+
+		if (net != c_net || !tc->t_sock)
+			continue;
+
+		rds_conn_drop(tc->conn); /* reconnect with new parameters */
+	}
+	spin_unlock_irq(&rds_tcp_conn_lock);
+}
+
+static int sndbuf_handler(struct ctl_table *ctl, int write,
+			  void __user *buffer, size_t *lenp, loff_t *fpos)
+{
+	struct net *net = current->nsproxy->net_ns;
+	struct rds_tcp_net *rtn = net_generic(net, rds_tcp_netid);
+	struct ctl_table tmp;
+
+	tmp = *ctl;
+	tmp.data = &rtn->sndbuf_size;
+	if (!write)
+		return proc_dointvec(&tmp, write, buffer, lenp, fpos);
+
+	rtn->sndbuf_size = max_t(u32, user_atoi(buffer, *lenp) * 2,
+				 SOCK_MIN_SNDBUF);