tcp: Fix data-races around sysctl_tcp_slow_start_after_idle.

While reading sysctl_tcp_slow_start_after_idle, it can be changed
concurrently.  Thus, we need to add READ_ONCE() to its readers.

Fixes: 35089bb203f4 ("[TCP]: Add tcp_slow_start_after_idle sysctl.")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 6ee1fb4..071735e 100644 (file)
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1403,8 +1403,8 @@ static inline void tcp_slow_start_after_idle_check(struct sock *sk)
        struct tcp_sock *tp = tcp_sk(sk);
        s32 delta;
 
-       if (!sock_net(sk)->ipv4.sysctl_tcp_slow_start_after_idle || tp->packets_out ||
-           ca_ops->cong_control)
+       if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_slow_start_after_idle) ||
+           tp->packets_out || ca_ops->cong_control)
                return;
        delta = tcp_jiffies32 - tp->lsndtime;
        if (delta > inet_csk(sk)->icsk_rto)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 898fcdc..5112040 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1898,7 +1898,7 @@ static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
                if (tp->packets_out > tp->snd_cwnd_used)
                        tp->snd_cwnd_used = tp->packets_out;
 
-               if (sock_net(sk)->ipv4.sysctl_tcp_slow_start_after_idle &&
+               if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_slow_start_after_idle) &&
                    (s32)(tcp_jiffies32 - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto &&
                    !ca_ops->cong_control)
                        tcp_cwnd_application_limited(sk);