tcp: Fix a data-race around sysctl_tcp_min_tso_segs.

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

Fixes: 95bd09e ("tcp: TSO packets automatic sizing")
Signed-off-by: Kuniyuki Iwashima <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: q2ven

net/ipv4/tcp_output.c

@@ -1995,7 +1995,7 @@ static u32 tcp_tso_segs(struct sock *sk, unsigned int mss_now)
 
 	min_tso = ca_ops->min_tso_segs ?
 			ca_ops->min_tso_segs(sk) :
-			sock_net(sk)->ipv4.sysctl_tcp_min_tso_segs;
+			READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_min_tso_segs);
 
 	tso_segs = tcp_tso_autosize(sk, mss_now, min_tso);
 	return min_t(u32, tso_segs, sk->sk_gso_max_segs);