netdev - [PATCH v2] tcp: fix tp->undo_retrans accounting in tcp_sacktag

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Message-Id: <1630248743-13361-1-git-send-email-zhenggy@chinatelecom.cn>
Date:   Sun, 29 Aug 2021 10:52:23 -0400
From:   zhenggy <zhenggy@...natelecom.cn>
To:     ncardwell@...gle.com, netdev@...r.kernel.org
Cc:     edumazet@...gle.com, davem@...emloft.net, yoshfuji@...ux-ipv6.org,
        dsahern@...nel.org, kuba@...nel.org, ycheng@...gle.com,
        zhenggy <zhenggy@...natelecom.cn>
Subject: [PATCH v2] tcp: fix tp->undo_retrans accounting in tcp_sacktag_one()

Commit a71d77e6be1e ("tcp: fix segment accounting when DSACK range covers
multiple segments") fix some DSACK accounting for multiple segments.
In tcp_sacktag_one(), we should also use the actual DSACK rang(pcount)
for tp->undo_retrans accounting.

Fixes: 10d3be569243 ("tcp-tso: do not split TSO packets at retransmit time")

Before that commit, the assumption underlying the tp->undo_retrans-- 
seems correct, AFAICT.

Signed-off-by: zhenggy <zhenggy@...natelecom.cn>
---
 net/ipv4/tcp_input.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 3f7bd7a..141e85e 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1346,7 +1346,7 @@ static u8 tcp_sacktag_one(struct sock *sk,
 	if (dup_sack && (sacked & TCPCB_RETRANS)) {
 		if (tp->undo_marker && tp->undo_retrans > 0 &&
 		    after(end_seq, tp->undo_marker))
-			tp->undo_retrans--;
+			tp->undo_retrans = max_t(int, 0, tp->undo_retrans - pcount);
 		if ((sacked & TCPCB_SACKED_ACKED) &&
 		    before(start_seq, state->reord))
 				state->reord = start_seq;
-- 
1.8.3.1