tcp: do not assume TCP code is non preemptible

We want to to make TCP stack preemptible, as draining prequeue
and backlog queues can take lot of time.

Many SNMP updates were assuming that BH (and preemption) was disabled.

Need to convert some __NET_INC_STATS() calls to NET_INC_STATS()
and some __TCP_INC_STATS() to TCP_INC_STATS()

Before using this_cpu_ptr(net->ipv4.tcp_sk) in tcp_v4_send_reset()
and tcp_v4_send_ack(), we add an explicit preempt disabled section.

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

1 files changed, 9 insertions, 5 deletions

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 87b173b563b0..761bc492c5e3 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -692,6 +692,7 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
                      offsetof(struct inet_timewait_sock, tw_bound_dev_if));
 
         arg.tos = ip_hdr(skb)->tos;
+        preempt_disable();
         ip_send_unicast_reply(*this_cpu_ptr(net->ipv4.tcp_sk),
                               skb, &TCP_SKB_CB(skb)->header.h4.opt,
                               ip_hdr(skb)->saddr, ip_hdr(skb)->daddr,
@@ -699,6 +700,7 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
 
         __TCP_INC_STATS(net, TCP_MIB_OUTSEGS);
         __TCP_INC_STATS(net, TCP_MIB_OUTRSTS);
+        preempt_enable();
 
 #ifdef CONFIG_TCP_MD5SIG
 out:
@@ -774,12 +776,14 @@ static void tcp_v4_send_ack(struct net *net,
         if (oif)
                 arg.bound_dev_if = oif;
         arg.tos = tos;
+        preempt_disable();
         ip_send_unicast_reply(*this_cpu_ptr(net->ipv4.tcp_sk),
                               skb, &TCP_SKB_CB(skb)->header.h4.opt,
                               ip_hdr(skb)->saddr, ip_hdr(skb)->daddr,
                               &arg, arg.iov[0].iov_len);
 
         __TCP_INC_STATS(net, TCP_MIB_OUTSEGS);
+        preempt_enable();
 }
 
 static void tcp_v4_timewait_ack(struct sock *sk, struct sk_buff *skb)
@@ -1151,12 +1155,12 @@ static bool tcp_v4_inbound_md5_hash(const struct sock *sk,
                 return false;
 
         if (hash_expected && !hash_location) {
-                __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5NOTFOUND);
+                NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5NOTFOUND);
                 return true;
         }
 
         if (!hash_expected && hash_location) {
-                __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5UNEXPECTED);
+                NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5UNEXPECTED);
                 return true;
         }
 
@@ -1342,7 +1346,7 @@ struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
         return newsk;
 
 exit_overflow:
-        __NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
+        NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
 exit_nonewsk:
         dst_release(dst);
 exit:
@@ -1432,8 +1436,8 @@ discard:
         return 0;
 
 csum_err:
-        __TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS);
-        __TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
+        TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS);
+        TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
         goto discard;
 }
 EXPORT_SYMBOL(tcp_v4_do_rcv);