From: Eric Dumazet <edumazet@google.com>
Date: Thu, 16 Apr 2026 20:03:07 +0000 (+0000)
Subject: tcp: add data-race annotations around tp->data_segs_out and tp->total_retrans
X-Git-Tag: v7.1-rc1~36^2~60^2~12
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=21e92a38cfd891538598ba8f805e0165a820d532;p=thirdparty%2Fkernel%2Fstable.git

tcp: add data-race annotations around tp->data_segs_out and tp->total_retrans

tcp_get_timestamping_opt_stats() intentionally runs lockless, we must
add READ_ONCE() and WRITE_ONCE() annotations to keep KCSAN happy.

Fixes: 7e98102f4897 ("tcp: record pkts sent and retransmistted")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260416200319.3608680-3-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 7b7812cb710f6..e39e0734d958f 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -4434,9 +4434,9 @@ struct sk_buff *tcp_get_timestamping_opt_stats(const struct sock *sk,
 	nla_put_u64_64bit(stats, TCP_NLA_SNDBUF_LIMITED,
 			  info.tcpi_sndbuf_limited, TCP_NLA_PAD);
 	nla_put_u64_64bit(stats, TCP_NLA_DATA_SEGS_OUT,
-			  tp->data_segs_out, TCP_NLA_PAD);
+			  READ_ONCE(tp->data_segs_out), TCP_NLA_PAD);
 	nla_put_u64_64bit(stats, TCP_NLA_TOTAL_RETRANS,
-			  tp->total_retrans, TCP_NLA_PAD);
+			  READ_ONCE(tp->total_retrans), TCP_NLA_PAD);
 
 	rate = READ_ONCE(sk->sk_pacing_rate);
 	rate64 = (rate != ~0UL) ? rate : ~0ULL;
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 8e99687526a64..d8e8bba2d03a3 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1688,7 +1688,8 @@ static int __tcp_transmit_skb(struct sock *sk, struct sk_buff *skb,
 
 	if (skb->len != tcp_header_size) {
 		tcp_event_data_sent(tp, sk);
-		tp->data_segs_out += tcp_skb_pcount(skb);
+		WRITE_ONCE(tp->data_segs_out,
+			   tp->data_segs_out + tcp_skb_pcount(skb));
 		tp->bytes_sent += skb->len - tcp_header_size;
 	}
 
@@ -3642,7 +3643,7 @@ start:
 	TCP_ADD_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS, segs);
 	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
-	tp->total_retrans += segs;
+	WRITE_ONCE(tp->total_retrans, tp->total_retrans + segs);
 	tp->bytes_retrans += skb->len;
 
 	/* make sure skb->data is aligned on arches that require it
@@ -4646,7 +4647,8 @@ int tcp_rtx_synack(const struct sock *sk, struct request_sock *req)
 			 * However in this case, we are dealing with a passive fastopen
 			 * socket thus we can change total_retrans value.
 			 */
-			tcp_sk_rw(sk)->total_retrans++;
+			WRITE_ONCE(tcp_sk_rw(sk)->total_retrans,
+				   tcp_sk_rw(sk)->total_retrans + 1);
 		}
 		trace_tcp_retransmit_synack(sk, req);
 		WRITE_ONCE(req->num_retrans, req->num_retrans + 1);