tcp: annotate data-races on tp->segs_in and tp->data_segs_in

tcp_segs_in() can be called from BH, while socket spinlock
is held but socket owned by user, eventually reading these
fields from tcp_get_info()

Found by code inspection, no need to backport this patch
to older kernels.
Signed-off-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/tcp.h

@@ -2172,9 +2172,13 @@ static inline void tcp_segs_in(struct tcp_sock *tp, const struct sk_buff *skb)
 	u16 segs_in;
 
 	segs_in = max_t(u16, 1, skb_shinfo(skb)->gso_segs);
-	tp->segs_in += segs_in;
+
+	/* We update these fields while other threads might
+	 * read them from tcp_get_info()
+	 */
+	WRITE_ONCE(tp->segs_in, tp->segs_in + segs_in);
 	if (skb->len > tcp_hdrlen(skb))
-		tp->data_segs_in += segs_in;
+		WRITE_ONCE(tp->data_segs_in, tp->data_segs_in + segs_in);
 }
 
 /*

net/ipv4/tcp.c

@@ -3769,10 +3769,12 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
 	tcp_get_info_chrono_stats(tp, info);
 
 	info->tcpi_segs_out = tp->segs_out;
-	info->tcpi_segs_in = tp->segs_in;
+
+	/* segs_in and data_segs_in can be updated from tcp_segs_in() from BH */
+	info->tcpi_segs_in = READ_ONCE(tp->segs_in);
+	info->tcpi_data_segs_in = READ_ONCE(tp->data_segs_in);
 
 	info->tcpi_min_rtt = tcp_min_rtt(tp);
-	info->tcpi_data_segs_in = tp->data_segs_in;
 	info->tcpi_data_segs_out = tp->data_segs_out;
 
 	info->tcpi_delivery_rate_app_limited = tp->rate_app_limited ? 1 : 0;