tcp: annotate tp->snd_nxt lockless reads

There are few places where we fetch tp->snd_nxt while
this field can change from IRQ or other cpu.

We need to add READ_ONCE() annotations, and also make
sure write sides use corresponding WRITE_ONCE() to avoid
store-tearing.

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

4 files changed, 13 insertions, 9 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 8e7c3f6801a9..e1d08f69fd39 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1917,7 +1917,8 @@ static inline u32 tcp_notsent_lowat(const struct tcp_sock *tp)
 static inline bool tcp_stream_memory_free(const struct sock *sk, int wake)
 {
         const struct tcp_sock *tp = tcp_sk(sk);
-        u32 notsent_bytes = READ_ONCE(tp->write_seq) - tp->snd_nxt;
+        u32 notsent_bytes = READ_ONCE(tp->write_seq) -
+                            READ_ONCE(tp->snd_nxt);
 
         return (notsent_bytes << wake) < tcp_notsent_lowat(tp);
 }
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 96dd65cbeb85..652568750cb1 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -625,7 +625,8 @@ int tcp_ioctl(struct sock *sk, int cmd, unsigned long arg)
                 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))
                         answ = 0;
                 else
-                        answ = READ_ONCE(tp->write_seq) - tp->snd_nxt;
+                        answ = READ_ONCE(tp->write_seq) -
+                               READ_ONCE(tp->snd_nxt);
                 break;
         default:
                 return -ENOIOCTLCMD;
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 339944690329..c802bc80c400 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -482,8 +482,10 @@ struct sock *tcp_create_openreq_child(const struct sock *sk,
         WRITE_ONCE(newtp->rcv_nxt, seq);
         newtp->segs_in = 1;
 
-        newtp->snd_sml = newtp->snd_una =
-        newtp->snd_nxt = newtp->snd_up = treq->snt_isn + 1;
+        seq = treq->snt_isn + 1;
+        newtp->snd_sml = newtp->snd_una = seq;
+        WRITE_ONCE(newtp->snd_nxt, seq);
+        newtp->snd_up = seq;
 
         INIT_LIST_HEAD(&newtp->tsq_node);
         INIT_LIST_HEAD(&newtp->tsorted_sent_queue);
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index c17c2a78809d..a115a991dfb5 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -67,7 +67,7 @@ static void tcp_event_new_data_sent(struct sock *sk, struct sk_buff *skb)
         struct tcp_sock *tp = tcp_sk(sk);
         unsigned int prior_packets = tp->packets_out;
 
-        tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
+        WRITE_ONCE(tp->snd_nxt, TCP_SKB_CB(skb)->end_seq);
 
         __skb_unlink(skb, &sk->sk_write_queue);
         tcp_rbtree_insert(&sk->tcp_rtx_queue, skb);
@@ -3142,7 +3142,7 @@ void tcp_send_fin(struct sock *sk)
                          * if FIN had been sent. This is because retransmit path
                          * does not change tp->snd_nxt.
                          */
-                        tp->snd_nxt++;
+                        WRITE_ONCE(tp->snd_nxt, tp->snd_nxt + 1);
                         return;
                 }
         } else {
@@ -3426,7 +3426,7 @@ static void tcp_connect_init(struct sock *sk)
         tp->snd_una = tp->write_seq;
         tp->snd_sml = tp->write_seq;
         tp->snd_up = tp->write_seq;
-        tp->snd_nxt = tp->write_seq;
+        WRITE_ONCE(tp->snd_nxt, tp->write_seq);
 
         if (likely(!tp->repair))
                 tp->rcv_nxt = 0;
@@ -3586,11 +3586,11 @@ int tcp_connect(struct sock *sk)
         /* We change tp->snd_nxt after the tcp_transmit_skb() call
          * in order to make this packet get counted in tcpOutSegs.
          */
-        tp->snd_nxt = tp->write_seq;
+        WRITE_ONCE(tp->snd_nxt, tp->write_seq);
         tp->pushed_seq = tp->write_seq;
         buff = tcp_send_head(sk);
         if (unlikely(buff)) {
-                tp->snd_nxt     = TCP_SKB_CB(buff)->seq;
+                WRITE_ONCE(tp->snd_nxt, TCP_SKB_CB(buff)->seq);
                 tp->pushed_seq  = TCP_SKB_CB(buff)->seq;
         }
         TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);