1 files changed, 44 insertions, 42 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 2877c3e09587..53c8ce4046b2 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -105,7 +105,6 @@ int sysctl_tcp_abc __read_mostly;
 #define FLAG_SYN_ACKED          0x10 /* This ACK acknowledged SYN.              */
 #define FLAG_DATA_SACKED        0x20 /* New SACK.                               */
 #define FLAG_ECE                0x40 /* ECE in this ACK                         */
-#define FLAG_DATA_LOST          0x80 /* SACK detected data lossage.             */
 #define FLAG_SLOWPATH           0x100 /* Do not skip RFC checks for window update.*/
 #define FLAG_ONLY_ORIG_SACKED   0x200 /* SACKs only non-rexmit sent before RTO */
 #define FLAG_SND_UNA_ADVANCED   0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
@@ -1040,13 +1039,11 @@ static void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp,
  * These 6 states form finite state machine, controlled by the following events:
  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
- * 3. Loss detection event of one of three flavors:
+ * 3. Loss detection event of two flavors:
  *      A. Scoreboard estimator decided the packet is lost.
  *         A'. Reno "three dupacks" marks head of queue lost.
- *         A''. Its FACK modfication, head until snd.fack is lost.
- *      B. SACK arrives sacking data transmitted after never retransmitted
- *         hole was sent out.
- *      C. SACK arrives sacking SND.NXT at the moment, when the
+ *         A''. Its FACK modification, head until snd.fack is lost.
+ *      B. SACK arrives sacking SND.NXT at the moment, when the
  *         segment was retransmitted.
  * 4. D-SACK added new rule: D-SACK changes any tag to S.
  *
@@ -1153,7 +1150,7 @@ static int tcp_is_sackblock_valid(struct tcp_sock *tp, int is_dsack,
 }
 
 /* Check for lost retransmit. This superb idea is borrowed from "ratehalving".
- * Event "C". Later note: FACK people cheated me again 8), we have to account
+ * Event "B". Later note: FACK people cheated me again 8), we have to account
  * for reordering! Ugly, but should help.
  *
  * Search retransmitted skbs from write_queue that were sent when snd_nxt was
@@ -1310,25 +1307,26 @@ static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
         return in_sack;
 }
 
-static u8 tcp_sacktag_one(const struct sk_buff *skb, struct sock *sk,
-                          struct tcp_sacktag_state *state,
+/* Mark the given newly-SACKed range as such, adjusting counters and hints. */
+static u8 tcp_sacktag_one(struct sock *sk,
+                          struct tcp_sacktag_state *state, u8 sacked,
+                          u32 start_seq, u32 end_seq,
                           int dup_sack, int pcount)
 {
         struct tcp_sock *tp = tcp_sk(sk);
-        u8 sacked = TCP_SKB_CB(skb)->sacked;
         int fack_count = state->fack_count;
 
         /* Account D-SACK for retransmitted packet. */
         if (dup_sack && (sacked & TCPCB_RETRANS)) {
                 if (tp->undo_marker && tp->undo_retrans &&
-                    after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
+                    after(end_seq, tp->undo_marker))
                         tp->undo_retrans--;
                 if (sacked & TCPCB_SACKED_ACKED)
                         state->reord = min(fack_count, state->reord);
         }
 
         /* Nothing to do; acked frame is about to be dropped (was ACKed). */
-        if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
+        if (!after(end_seq, tp->snd_una))
                 return sacked;
 
         if (!(sacked & TCPCB_SACKED_ACKED)) {
@@ -1347,13 +1345,13 @@ static u8 tcp_sacktag_one(const struct sk_buff *skb, struct sock *sk,
                                 /* New sack for not retransmitted frame,
                                  * which was in hole. It is reordering.
                                  */
-                                if (before(TCP_SKB_CB(skb)->seq,
+                                if (before(start_seq,
                                            tcp_highest_sack_seq(tp)))
                                         state->reord = min(fack_count,
                                                            state->reord);
 
                                 /* SACK enhanced F-RTO (RFC4138; Appendix B) */
-                                if (!after(TCP_SKB_CB(skb)->end_seq, tp->frto_highmark))
+                                if (!after(end_seq, tp->frto_highmark))
                                         state->flag |= FLAG_ONLY_ORIG_SACKED;
                         }
 
@@ -1371,8 +1369,7 @@ static u8 tcp_sacktag_one(const struct sk_buff *skb, struct sock *sk,
 
                 /* Lost marker hint past SACKed? Tweak RFC3517 cnt */
                 if (!tcp_is_fack(tp) && (tp->lost_skb_hint != NULL) &&
-                    before(TCP_SKB_CB(skb)->seq,
-                           TCP_SKB_CB(tp->lost_skb_hint)->seq))
+                    before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
                         tp->lost_cnt_hint += pcount;
 
                 if (fack_count > tp->fackets_out)
@@ -1391,6 +1388,9 @@ static u8 tcp_sacktag_one(const struct sk_buff *skb, struct sock *sk,
         return sacked;
 }
 
+/* Shift newly-SACKed bytes from this skb to the immediately previous
+ * already-SACKed sk_buff. Mark the newly-SACKed bytes as such.
+ */
 static int tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
                            struct tcp_sacktag_state *state,
                            unsigned int pcount, int shifted, int mss,
@@ -1398,10 +1398,13 @@ static int tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
 {
         struct tcp_sock *tp = tcp_sk(sk);
         struct sk_buff *prev = tcp_write_queue_prev(sk, skb);
+        u32 start_seq = TCP_SKB_CB(skb)->seq;   /* start of newly-SACKed */
+        u32 end_seq = start_seq + shifted;      /* end of newly-SACKed */
 
         BUG_ON(!pcount);
 
-        if (skb == tp->lost_skb_hint)
+        /* Adjust hint for FACK. Non-FACK is handled in tcp_sacktag_one(). */
+        if (tcp_is_fack(tp) && (skb == tp->lost_skb_hint))
                 tp->lost_cnt_hint += pcount;
 
         TCP_SKB_CB(prev)->end_seq += shifted;
@@ -1427,8 +1430,11 @@ static int tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
                 skb_shinfo(skb)->gso_type = 0;
         }
 
-        /* We discard results */
-        tcp_sacktag_one(skb, sk, state, dup_sack, pcount);
+        /* Adjust counters and hints for the newly sacked sequence range but
+         * discard the return value since prev is already marked.
+         */
+        tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
+                        start_seq, end_seq, dup_sack, pcount);
 
         /* Difference in this won't matter, both ACKed by the same cumul. ACK */
         TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
@@ -1667,10 +1673,14 @@ static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
                         break;
 
                 if (in_sack) {
-                        TCP_SKB_CB(skb)->sacked = tcp_sacktag_one(skb, sk,
-                                                                  state,
-                                                                  dup_sack,
-                                                                  tcp_skb_pcount(skb));
+                        TCP_SKB_CB(skb)->sacked =
+                                tcp_sacktag_one(sk,
+                                                state,
+                                                TCP_SKB_CB(skb)->sacked,
+                                                TCP_SKB_CB(skb)->seq,
+                                                TCP_SKB_CB(skb)->end_seq,
+                                                dup_sack,
+                                                tcp_skb_pcount(skb));
 
                         if (!before(TCP_SKB_CB(skb)->seq,
                                     tcp_highest_sack_seq(tp)))
@@ -1844,10 +1854,6 @@ tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
                 if (found_dup_sack && ((i + 1) == first_sack_index))
                         next_dup = &sp[i + 1];
 
-                /* Event "B" in the comment above. */
-                if (after(end_seq, tp->high_seq))
-                        state.flag |= FLAG_DATA_LOST;
-
                 /* Skip too early cached blocks */
                 while (tcp_sack_cache_ok(tp, cache) &&
                        !before(start_seq, cache->end_seq))
@@ -2515,8 +2521,11 @@ static void tcp_timeout_skbs(struct sock *sk)
         tcp_verify_left_out(tp);
 }
 
-/* Mark head of queue up as lost. With RFC3517 SACK, the packets is
- * is against sacked "cnt", otherwise it's against facked "cnt"
+/* Detect loss in event "A" above by marking head of queue up as lost.
+ * For FACK or non-SACK(Reno) senders, the first "packets" number of segments
+ * are considered lost. For RFC3517 SACK, a segment is considered lost if it
+ * has at least tp->reordering SACKed seqments above it; "packets" refers to
+ * the maximum SACKed segments to pass before reaching this limit.
  */
 static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
 {
@@ -2525,6 +2534,8 @@ static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
         int cnt, oldcnt;
         int err;
         unsigned int mss;
+        /* Use SACK to deduce losses of new sequences sent during recovery */
+        const u32 loss_high = tcp_is_sack(tp) ?  tp->snd_nxt : tp->high_seq;
 
         WARN_ON(packets > tp->packets_out);
         if (tp->lost_skb_hint) {
@@ -2546,7 +2557,7 @@ static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
                 tp->lost_skb_hint = skb;
                 tp->lost_cnt_hint = cnt;
 
-                if (after(TCP_SKB_CB(skb)->end_seq, tp->high_seq))
+                if (after(TCP_SKB_CB(skb)->end_seq, loss_high))
                         break;
 
                 oldcnt = cnt;
@@ -3033,19 +3044,10 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
         if (tcp_check_sack_reneging(sk, flag))
                 return;
 
-        /* C. Process data loss notification, provided it is valid. */
-        if (tcp_is_fack(tp) && (flag & FLAG_DATA_LOST) &&
-            before(tp->snd_una, tp->high_seq) &&
-            icsk->icsk_ca_state != TCP_CA_Open &&
-            tp->fackets_out > tp->reordering) {
-                tcp_mark_head_lost(sk, tp->fackets_out - tp->reordering, 0);
-                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSS);
-        }
-
-        /* D. Check consistency of the current state. */
+        /* C. Check consistency of the current state. */
         tcp_verify_left_out(tp);
 
-        /* E. Check state exit conditions. State can be terminated
+        /* D. Check state exit conditions. State can be terminated
          *    when high_seq is ACKed. */
         if (icsk->icsk_ca_state == TCP_CA_Open) {
                 WARN_ON(tp->retrans_out != 0);
@@ -3077,7 +3079,7 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
                 }
         }
 
-        /* F. Process state. */
+        /* E. Process state. */
         switch (icsk->icsk_ca_state) {
         case TCP_CA_Recovery:
                 if (!(flag & FLAG_SND_UNA_ADVANCED)) {