Patch "tcp: tcp_mark_head_lost is only valid for sack-tcp" has been added to the 4.19-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    tcp: tcp_mark_head_lost is only valid for sack-tcp

to the 4.19-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     tcp-tcp_mark_head_lost-is-only-valid-for-sack-tcp.patch
and it can be found in the queue-4.19 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit e54288a45229e4435add827417471cfc86b1ead3
Author: zhang kai <zhangkaiheb@xxxxxxx>
Date:   Thu May 7 11:08:30 2020 +0800

    tcp: tcp_mark_head_lost is only valid for sack-tcp
    
    [ Upstream commit 636ef28d6e4d174e424102466caf572b0406fb0e ]
    
    so tcp_is_sack/reno checks are removed from tcp_mark_head_lost.
    
    Signed-off-by: zhang kai <zhangkaiheb@xxxxxxx>
    Acked-by: Neal Cardwell <ncardwell@xxxxxxxxxx>
    Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
    Stable-dep-of: a6458ab7fd4f ("UPSTREAM: tcp: fix DSACK undo in fast recovery to call tcp_try_to_open()")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 022d75c67096a..e51aa5a149c0f 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2193,8 +2193,7 @@ static bool tcp_time_to_recover(struct sock *sk, int flag)
 }
 
 /* Detect loss in event "A" above by marking head of queue up as lost.
- * For non-SACK(Reno) senders, the first "packets" number of segments
- * are considered lost. For RFC3517 SACK, a segment is considered lost if it
+ * 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.
  */
@@ -2202,10 +2201,9 @@ static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct sk_buff *skb;
-	int cnt, oldcnt, lost;
-	unsigned int mss;
+	int cnt;
 	/* 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;
+	const u32 loss_high = tp->snd_nxt;
 
 	WARN_ON(packets > tp->packets_out);
 	skb = tp->lost_skb_hint;
@@ -2228,26 +2226,11 @@ static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
 		if (after(TCP_SKB_CB(skb)->end_seq, loss_high))
 			break;
 
-		oldcnt = cnt;
-		if (tcp_is_reno(tp) ||
-		    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
+		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
 			cnt += tcp_skb_pcount(skb);
 
-		if (cnt > packets) {
-			if (tcp_is_sack(tp) ||
-			    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) ||
-			    (oldcnt >= packets))
-				break;
-
-			mss = tcp_skb_mss(skb);
-			/* If needed, chop off the prefix to mark as lost. */
-			lost = (packets - oldcnt) * mss;
-			if (lost < skb->len &&
-			    tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb,
-					 lost, mss, GFP_ATOMIC) < 0)
-				break;
-			cnt = packets;
-		}
+		if (cnt > packets)
+			break;
 
 		tcp_skb_mark_lost(tp, skb);
 
@@ -2874,8 +2857,7 @@ static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
 			if (tcp_try_undo_partial(sk, prior_snd_una))
 				return;
 			/* Partial ACK arrived. Force fast retransmit. */
-			do_lost = tcp_is_reno(tp) ||
-				  tcp_force_fast_retransmit(sk);
+			do_lost = tcp_force_fast_retransmit(sk);
 		}
 		if (tcp_try_undo_dsack(sk)) {
 			tcp_try_keep_open(sk);