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.)

Fixes: 6ba8a3b19e76 ("tcp: Tail loss probe (TLP)")
Signed-off-by: Neal Cardwell <ncardw...@google.com>
Signed-off-by: Yuchung Cheng <ych...@google.com>
Signed-off-by: Nandita Dukkipati <nandi...@google.com>
Acked-by: Eric Dumazet <eduma...@google.com>
---
 include/net/tcp.h    | 10 ++++++++++
 net/ipv4/tcp_input.c |  5 +----
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 70483296157f..ada65e767b28 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1916,6 +1916,16 @@ extern void tcp_rack_advance(struct tcp_sock *tp, u8 
sacked, u32 end_seq,
                             u64 xmit_time);
 extern void tcp_rack_reo_timeout(struct sock *sk);
 
+/* At how many usecs into the future should the RTO fire? */
+static inline s64 tcp_rto_delta_us(const struct sock *sk)
+{
+       const struct sk_buff *skb = tcp_write_queue_head(sk);
+       u32 rto = inet_csk(sk)->icsk_rto;
+       u64 rto_time_stamp_us = skb->skb_mstamp + jiffies_to_usecs(rto);
+
+       return rto_time_stamp_us - tcp_sk(sk)->tcp_mstamp;
+}
+
 /*
  * Save and compile IPv4 options, return a pointer to it
  */
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index dad026fcfd09..b9ba8d55d8b8 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3004,10 +3004,7 @@ void tcp_rearm_rto(struct sock *sk)
                /* Offset the time elapsed after installing regular RTO */
                if (icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||
                    icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
-                       struct sk_buff *skb = tcp_write_queue_head(sk);
-                       u64 rto_time_stamp = skb->skb_mstamp +
-                                            jiffies_to_usecs(rto);
-                       s64 delta_us = rto_time_stamp - tp->tcp_mstamp;
+                       s64 delta_us = tcp_rto_delta_us(sk);
                        /* delta_us may not be positive if the socket is locked
                         * when the retrans timer fires and is rescheduled.
                         */
-- 
2.14.0.rc1.383.gd1ce394fe2-goog

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