2024-12-10 06:44:25 +03:00
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From ab109789c18f7edf7a34923398a64ba7ba38cc6c Mon Sep 17 00:00:00 2001
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2024-10-29 05:12:06 +03:00
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From: Neal Cardwell <ncardwell@google.com>
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Date: Wed, 1 May 2019 20:16:33 -0400
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Subject: [PATCH 07/19] net-tcp_bbr: v2: adjust skb tx.in_flight upon merge in
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tcp_shifted_skb()
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When tcp_shifted_skb() updates state as adjacent SACKed skbs are
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coalesced, previously the tx.in_flight was not adjusted, so we could
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get contradictory state where the skb's recorded pcount was bigger
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than the tx.in_flight (the number of segments that were in_flight
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after sending the skb).
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Normally have a SACKed skb with contradictory pcount/tx.in_flight
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would not matter. However, with SACK reneging, the SACKed bit is
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removed, and an skb once again becomes eligible for retransmitting,
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fragmenting, SACKing, etc. Packetdrill testing verified the following
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sequence is possible in a kernel that does not have this commit:
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- skb N is SACKed
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- skb N+1 is SACKed and combined with skb N using tcp_shifted_skb()
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- tcp_shifted_skb() will increase the pcount of prev,
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but leave tx.in_flight as-is
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- so prev skb can have pcount > tx.in_flight
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- RTO, tcp_timeout_mark_lost(), detect reneg,
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remove "SACKed" bit, mark skb N as lost
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- find pcount of skb N is greater than its tx.in_flight
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I suspect this issue iw what caused the bbr2_inflight_hi_from_lost_skb():
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WARN_ON_ONCE(inflight_prev < 0)
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to fire in production machines using bbr2.
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Effort: net-tcp_bbr
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Origin-9xx-SHA1: 1a3e997e613d2dcf32b947992882854ebe873715
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Change-Id: I1b0b75c27519953430c7db51c6f358f104c7af55
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Signed-off-by: Alexandre Frade <kernel@xanmod.org>
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---
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net/ipv4/tcp_input.c | 11 +++++++++++
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1 file changed, 11 insertions(+)
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--- a/net/ipv4/tcp_input.c
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+++ b/net/ipv4/tcp_input.c
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@@ -1506,6 +1506,17 @@ static bool tcp_shifted_skb(struct sock
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WARN_ON_ONCE(tcp_skb_pcount(skb) < pcount);
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tcp_skb_pcount_add(skb, -pcount);
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+ /* Adjust tx.in_flight as pcount is shifted from skb to prev. */
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+ if (WARN_ONCE(TCP_SKB_CB(skb)->tx.in_flight < pcount,
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+ "prev in_flight: %u skb in_flight: %u pcount: %u",
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+ TCP_SKB_CB(prev)->tx.in_flight,
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+ TCP_SKB_CB(skb)->tx.in_flight,
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+ pcount))
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+ TCP_SKB_CB(skb)->tx.in_flight = 0;
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+ else
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+ TCP_SKB_CB(skb)->tx.in_flight -= pcount;
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+ TCP_SKB_CB(prev)->tx.in_flight += pcount;
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+
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/* When we're adding to gso_segs == 1, gso_size will be zero,
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* in theory this shouldn't be necessary but as long as DSACK
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* code can come after this skb later on it's better to keep
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