tcp: fix SO_RCVLOWAT and RCVBUF autotuning

Applications might use SO_RCVLOWAT on TCP socket hoping to receive
one [E]POLLIN event only when a given amount of bytes are ready in socket
receive queue.

Problem is that receive autotuning is not aware of this constraint,
meaning sk_rcvbuf might be too small to allow all bytes to be stored.

Add a new (struct proto_ops)->set_rcvlowat method so that a protocol
can override the default setsockopt(SO_RCVLOWAT) behavior.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/net.h b/include/linux/net.h
index 2248a05..6554d3b 100644 (file)
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -197,6 +197,7 @@ struct proto_ops {
                                           int offset, size_t size, int flags);
        int             (*sendmsg_locked)(struct sock *sk, struct msghdr *msg,
                                          size_t size);
+       int             (*set_rcvlowat)(struct sock *sk, int val);
 };
 
 #define DECLARE_SOCKADDR(type, dst, src)       \

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 9c9b376..b231824 100644 (file)
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -402,6 +402,7 @@ void tcp_set_keepalive(struct sock *sk, int val);
 void tcp_syn_ack_timeout(const struct request_sock *req);
 int tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int nonblock,
                int flags, int *addr_len);
+int tcp_set_rcvlowat(struct sock *sk, int val);
 void tcp_parse_options(const struct net *net, const struct sk_buff *skb,
                       struct tcp_options_received *opt_rx,
                       int estab, struct tcp_fastopen_cookie *foc);

diff --git a/net/core/sock.c b/net/core/sock.c
index 6444525..b2c3db1 100644 (file)
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -905,7 +905,10 @@ set_rcvbuf:
        case SO_RCVLOWAT:
                if (val < 0)
                        val = INT_MAX;
-               sk->sk_rcvlowat = val ? : 1;
+               if (sock->ops->set_rcvlowat)
+                       ret = sock->ops->set_rcvlowat(sk, val);
+               else
+                       sk->sk_rcvlowat = val ? : 1;
                break;
 
        case SO_RCVTIMEO:

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index eaed036..f5c562a 100644 (file)
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1006,6 +1006,7 @@ const struct proto_ops inet_stream_ops = {
        .compat_getsockopt = compat_sock_common_getsockopt,
        .compat_ioctl      = inet_compat_ioctl,
 #endif
+       .set_rcvlowat      = tcp_set_rcvlowat,
 };
 EXPORT_SYMBOL(inet_stream_ops);
 

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index bccc4c2..0abd8d1 100644 (file)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1701,6 +1701,27 @@ int tcp_peek_len(struct socket *sock)
 }
 EXPORT_SYMBOL(tcp_peek_len);
 
+/* Make sure sk_rcvbuf is big enough to satisfy SO_RCVLOWAT hint */
+int tcp_set_rcvlowat(struct sock *sk, int val)
+{
+       sk->sk_rcvlowat = val ? : 1;
+       if (sk->sk_userlocks & SOCK_RCVBUF_LOCK)
+               return 0;
+
+       /* val comes from user space and might be close to INT_MAX */
+       val <<= 1;
+       if (val < 0)
+               val = INT_MAX;
+
+       val = min(val, sock_net(sk)->ipv4.sysctl_tcp_rmem[2]);
+       if (val > sk->sk_rcvbuf) {
+               sk->sk_rcvbuf = val;
+               tcp_sk(sk)->window_clamp = tcp_win_from_space(sk, val);
+       }
+       return 0;
+}
+EXPORT_SYMBOL(tcp_set_rcvlowat);
+
 static void tcp_update_recv_tstamps(struct sk_buff *skb,
                                    struct scm_timestamping *tss)
 {

diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
index 8da0b51..e70d59f 100644 (file)
--- a/net/ipv6/af_inet6.c
+++ b/net/ipv6/af_inet6.c
@@ -590,6 +590,7 @@ const struct proto_ops inet6_stream_ops = {
        .compat_setsockopt = compat_sock_common_setsockopt,
        .compat_getsockopt = compat_sock_common_getsockopt,
 #endif
+       .set_rcvlowat      = tcp_set_rcvlowat,
 };
 
 const struct proto_ops inet6_dgram_ops = {