[PATCH net 6/9] tcp: annotate tp->urg_seq lockless reads

[Eric Dumazet]

There two places where we fetch tp->urg_seq while
this field can change from IRQ or other cpu.

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

Signed-off-by: Eric Dumazet <eduma...@google.com>
---
 net/ipv4/tcp.c       | 5 +++--
 net/ipv4/tcp_input.c | 2 +-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 
652568750cb17268509efc83bfa4bae0a23be83d..577a8c6eef9f520ba5d96485ab866af89aa0a046
 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -546,7 +546,7 @@ __poll_t tcp_poll(struct file *file, struct socket *sock, 
poll_table *wait)
            (state != TCP_SYN_RECV || rcu_access_pointer(tp->fastopen_rsk))) {
                int target = sock_rcvlowat(sk, 0, INT_MAX);
 
-               if (tp->urg_seq == READ_ONCE(tp->copied_seq) &&
+               if (READ_ONCE(tp->urg_seq) == READ_ONCE(tp->copied_seq) &&
                    !sock_flag(sk, SOCK_URGINLINE) &&
                    tp->urg_data)
                        target++;
@@ -607,7 +607,8 @@ int tcp_ioctl(struct sock *sk, int cmd, unsigned long arg)
                unlock_sock_fast(sk, slow);
                break;
        case SIOCATMARK:
-               answ = tp->urg_data && tp->urg_seq == READ_ONCE(tp->copied_seq);
+               answ = tp->urg_data &&
+                      READ_ONCE(tp->urg_seq) == READ_ONCE(tp->copied_seq);
                break;
        case SIOCOUTQ:
                if (sk->sk_state == TCP_LISTEN)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 
a30aae3a6a182a3ba3d262171ebd9c1441cd5cd6..16342e043ab353bfe1b10d8099117395a396fbd4
 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5356,7 +5356,7 @@ static void tcp_check_urg(struct sock *sk, const struct 
tcphdr *th)
        }
 
        tp->urg_data = TCP_URG_NOTYET;
-       tp->urg_seq = ptr;
+       WRITE_ONCE(tp->urg_seq, ptr);
 
        /* Disable header prediction. */
        tp->pred_flags = 0;
-- 
2.23.0.700.g56cf767bdb-goog