[PATCH 3.10 008/139] tcp: introduce tcp_rto_delta_us() helper for xmit timer fix

[Willy Tarreau]

From: Neal Cardwell <ncardwell@xxxxxxxxxx>

commit e1a10ef7fa876f8510aaec36ea5c0cf34baba410 upstream.

Pure refactor. This helper will be required in the xmit timer fix
later in the patch series. (Because the TLP logic will want to make
this calculation.)

[This version of the commit was compiled and briefly tested
based on top of v3.10.107.]

Change-Id: I1ccfba0b00465454bf5ce22e6fef5f7b5dd94d15
Fixes: 6ba8a3b19e76 ("tcp: Tail loss probe (TLP)")
Signed-off-by: Neal Cardwell <ncardwell@xxxxxxxxxx>
Signed-off-by: Yuchung Cheng <ycheng@xxxxxxxxxx>
Signed-off-by: Nandita Dukkipati <nanditad@xxxxxxxxxx>
Acked-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: Willy Tarreau <w@xxxxxx>
---
 include/net/tcp.h    | 10 ++++++++++
 net/ipv4/tcp_input.c |  4 +---
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 79cd118..c4db9ac 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1592,4 +1592,14 @@ struct tcp_request_sock_ops {
 extern void tcp_v4_init(void);
 extern void tcp_init(void);
 
+/* At how many jiffies into the future should the RTO fire? */
+static inline s32 tcp_rto_delta(const struct sock *sk)
+{
+	const struct sk_buff *skb = tcp_write_queue_head(sk);
+	const u32 rto = inet_csk(sk)->icsk_rto;
+	const u32 rto_time_stamp = TCP_SKB_CB(skb)->when + rto;
+
+	return (s32)(rto_time_stamp - tcp_time_stamp);
+}
+
 #endif	/* _TCP_H */
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 0680058..a36b7c5 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2972,9 +2972,7 @@ void tcp_rearm_rto(struct sock *sk)
 		/* Offset the time elapsed after installing regular RTO */
 		if (icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
 		    icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
-			struct sk_buff *skb = tcp_write_queue_head(sk);
-			const u32 rto_time_stamp = TCP_SKB_CB(skb)->when + rto;
-			s32 delta = (s32)(rto_time_stamp - tcp_time_stamp);
+			s32 delta = tcp_rto_delta(sk);
 			/* delta may not be positive if the socket is locked
 			 * when the retrans timer fires and is rescheduled.
 			 */
-- 
2.8.0.rc2.1.gbe9624a