tcp: Fix a data-race around sysctl_tcp_tso_rtt_log.

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

Fixes: 6546690 ("tcp: adjust TSO packet sizes based on min_rtt")
Signed-off-by: Kuniyuki Iwashima <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: q2ven

net/ipv4/tcp_output.c

@@ -1976,7 +1976,7 @@ static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
 
 	bytes = sk->sk_pacing_rate >> READ_ONCE(sk->sk_pacing_shift);
 
-	r = tcp_min_rtt(tcp_sk(sk)) >> sock_net(sk)->ipv4.sysctl_tcp_tso_rtt_log;
+	r = tcp_min_rtt(tcp_sk(sk)) >> READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_tso_rtt_log);
 	if (r < BITS_PER_TYPE(sk->sk_gso_max_size))
 		bytes += sk->sk_gso_max_size >> r;