3 files changed, 19 insertions, 34 deletions

diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c
index e16f9bb9eaaf..0bb338be9dd7 100644
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -448,7 +448,7 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
                  * Calculate new round trip sample as per [RFC 3448, 4.3] by
                  *      R_sample  =  (now - t_recvdata) - t_elapsed
                  */
-                r_sample = dccp_sample_rtt(sk, now, &packet->dccphtx_tstamp);
+                r_sample = dccp_sample_rtt(sk, ktime_us_delta(now, packet->dccphtx_tstamp));
 
                 /*
                  * Update RTT estimate by
@@ -881,9 +881,9 @@ static void ccid3_hc_rx_packet_recv(struct sock *sk, struct sk_buff *skb)
         case DCCP_PKT_DATAACK:
                 if (opt_recv->dccpor_timestamp_echo == 0)
                         break;
+                r_sample = dccp_timestamp() - opt_recv->dccpor_timestamp_echo;
                 rtt_prev = hcrx->ccid3hcrx_rtt;
-                now = ktime_get_real();
-                r_sample = dccp_sample_rtt(sk, now, NULL);
+                r_sample = dccp_sample_rtt(sk, 10 * r_sample);
 
                 if (hcrx->ccid3hcrx_state == TFRC_RSTATE_NO_DATA)
                         hcrx->ccid3hcrx_rtt = r_sample;
diff --git a/net/dccp/dccp.h b/net/dccp/dccp.h
index a75c740ae6c0..bd4645b3a36c 100644
--- a/net/dccp/dccp.h
+++ b/net/dccp/dccp.h
@@ -297,8 +297,7 @@ extern int	   dccp_v4_connect(struct sock *sk, struct sockaddr *uaddr,
 extern int         dccp_send_reset(struct sock *sk, enum dccp_reset_codes code);
 extern void        dccp_send_close(struct sock *sk, const int active);
 extern int         dccp_invalid_packet(struct sk_buff *skb);
-extern u32         dccp_sample_rtt(struct sock *sk, ktime_t t_recv,
-                                   ktime_t *t_history);
+extern u32         dccp_sample_rtt(struct sock *sk, long delta);
 
 static inline int dccp_bad_service_code(const struct sock *sk,
                                         const __be32 service)
diff --git a/net/dccp/input.c b/net/dccp/input.c
index 782cdb7292fa..3b651701cfe4 100644
--- a/net/dccp/input.c
+++ b/net/dccp/input.c
@@ -280,6 +280,7 @@ static int dccp_rcv_request_sent_state_process(struct sock *sk,
         if (dh->dccph_type == DCCP_PKT_RESPONSE) {
                 const struct inet_connection_sock *icsk = inet_csk(sk);
                 struct dccp_sock *dp = dccp_sk(sk);
+                long tstamp = dccp_timestamp();
 
                 /* Stop the REQUEST timer */
                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
@@ -300,11 +301,10 @@ static int dccp_rcv_request_sent_state_process(struct sock *sk,
                 if (dccp_parse_options(sk, skb))
                         goto out_invalid_packet;
 
-                /* Obtain RTT sample from SYN exchange (used by CCID 3) */
-                if (dp->dccps_options_received.dccpor_timestamp_echo)
-                        dp->dccps_syn_rtt = dccp_sample_rtt(sk,
-                                                            ktime_get_real(),
-                                                            NULL);
+                /* Obtain usec RTT sample from SYN exchange (used by CCID 3) */
+                if (likely(dp->dccps_options_received.dccpor_timestamp_echo))
+                        dp->dccps_syn_rtt = dccp_sample_rtt(sk, 10 * (tstamp -
+                            dp->dccps_options_received.dccpor_timestamp_echo));
 
                 if (dccp_msk(sk)->dccpms_send_ack_vector &&
                     dccp_ackvec_add(dp->dccps_hc_rx_ackvec, sk,
@@ -585,36 +585,22 @@ discard:
 EXPORT_SYMBOL_GPL(dccp_rcv_state_process);
 
 /**
- * dccp_sample_rtt  -  Sample RTT from packet exchange
- *
- * @sk:     connected dccp_sock
- * @t_recv: receive timestamp of packet with timestamp echo
- * @t_hist: packet history timestamp or NULL
+ *  dccp_sample_rtt  -  Validate and finalise computation of RTT sample
+ *  @delta:     number of microseconds between packet and acknowledgment
+ *  The routine is kept generic to work in different contexts. It should be
+ *  called immediately when the ACK used for the RTT sample arrives.
  */
-u32 dccp_sample_rtt(struct sock *sk, ktime_t t_recv, ktime_t *t_hist)
+u32 dccp_sample_rtt(struct sock *sk, long delta)
 {
-        struct dccp_sock *dp = dccp_sk(sk);
-        struct dccp_options_received *or = &dp->dccps_options_received;
-        s64 delta;
-
-        if (t_hist == NULL) {
-                if (!or->dccpor_timestamp_echo) {
-                        DCCP_WARN("packet without timestamp echo\n");
-                        return DCCP_SANE_RTT_MAX;
-                }
-                ktime_sub_us(t_recv, or->dccpor_timestamp_echo * 10);
-                delta = ktime_to_us(t_recv);
-        } else
-                delta = ktime_us_delta(t_recv, *t_hist);
-
-        delta -= or->dccpor_elapsed_time * 10;          /* either set or 0 */
+        /* dccpor_elapsed_time is either zeroed out or set and > 0 */
+        delta -= dccp_sk(sk)->dccps_options_received.dccpor_elapsed_time * 10;
 
         if (unlikely(delta <= 0)) {
-                DCCP_WARN("unusable RTT sample %ld, using min\n", (long)delta);
+                DCCP_WARN("unusable RTT sample %ld, using min\n", delta);
                 return DCCP_SANE_RTT_MIN;
         }
-        if (unlikely(delta - (s64)DCCP_SANE_RTT_MAX > 0)) {
-                DCCP_WARN("RTT sample %ld too large, using max\n", (long)delta);
+        if (unlikely(delta > DCCP_SANE_RTT_MAX)) {
+                DCCP_WARN("RTT sample %ld too large, using max\n", delta);
                 return DCCP_SANE_RTT_MAX;
         }