[PATCH net 2/2] rxrpc: Fix RACK-TLP implementation
From: David Howells <dhowells@redhat.com>
Date: 2026-09-25 19:15:55
Also in:
lkml, stable
Subsystem:
networking [general], rxrpc sockets (af_rxrpc), the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, David Howells, Marc Dionne, Linus Torvalds
Fix the RACK-TLP implementation in the following ways:
(1) Move the "in/exiting Fast or RTO recovery" flags to the rxrpc_call
struct rather than rxrpc_ack_summary so that they persist beyond ACK
parsing to the next time rxrpc_congestion_management() happens (when
the next ACK is parsed). This allows those values to be accessed by
RACK-TLP when invoked by the Reorder timer expiring.
(2) In rxrpc_input_call_event(), rearm the RTO timer before the function
returns if no other timer is running and if DATA packets have been
sent but not yet ACK'd. This prevents us not having a timer set to
drive retransmission.
(3) In rxrpc_congestion_management(), initialise the TLP state when
entering the FAST_RETRANSMIT congestion control state, not every time
we process that state - otherwise TLP doesn't happen in that state.
(4) Don't reset segment_xmit_ts in rxrpc_rack_mark_lost() as that's called
from two places, one of which shouldn't do that. Instead, do it in
rxrpc_rack_detect_loss().
(5) In rxrpc_tlp_calc_pto(), check flight_size is at most one jumbo
packet's worth of subpackets in size, not just any non-zero value
(RFC8985 7.2 has a comparison against 1, so this is approximated
because we'll be sending jumbo packets if possible).
(6) In rxrpc_prepare_data_packet(), only increment call->tx_nr_resent if
the DATA packet being retransmitted was not previously transmitted
otherwise tx_nr_resent will keep getting bigger and cause RACK-TLP to
malfunction (the value is used in the in-flight calculation).
tx_nr_resent is decremented when a packet that has been retransmitted
is discarded - but only by 1 per packet.
Fixes: 7c482665931b ("rxrpc: Implement RACK/TLP to deal with transmission stalls [RFC8985]")
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Marc Dionne <marc.dionne@auristor.com>
Tested-by: Marc Dionne <marc.dionne@auristor.com>
Reviewed-by: Jeffrey Altman <redacted>
cc: Eric Dumazet <edumazet@google.com>
cc: "David S. Miller" <davem@davemloft.net>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
cc: stable@vger.kernel.org
---
net/rxrpc/ar-internal.h | 4 ++--
net/rxrpc/call_event.c | 13 +++++++++++++
net/rxrpc/input.c | 10 ++++++----
net/rxrpc/input_rack.c | 8 ++++----
net/rxrpc/output.c | 4 ++--
5 files changed, 27 insertions(+), 12 deletions(-)
diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index f0c8cbcc5dd5..9c7b2e0817e7 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h@@ -818,6 +818,8 @@ struct rxrpc_call { u16 cong_dup_acks; /* Count of ACKs showing missing packets */ u16 cong_cumul_acks; /* Cumulative ACK count */ ktime_t cong_tstamp; /* Last time cwnd was changed */ + bool cong_in_recovery:1; /* If we're in Fast/RTO recovery */ + bool cong_exiting_recovery:1; /* If we're leaving Fast/RTO recovery */ /* RACK-TLP [RFC8985] state. */ ktime_t rack_xmit_ts; /* Latest transmission timestamp */
@@ -896,8 +898,6 @@ struct rxrpc_ack_summary { bool retrans_timeo:1; /* T if reTx due to timeout happened */ bool need_retransmit:1; /* T if we need transmission */ bool rtt_sample_avail:1; /* T if RTT sample available */ - bool in_fast_or_rto_recovery:1; - bool exiting_fast_or_rto_recovery:1; bool tlp_probe_acked:1; /* T if the TLP probe seq was acked */ u8 /*enum rxrpc_congest_change*/ change; };
diff --git a/net/rxrpc/call_event.c b/net/rxrpc/call_event.c
index 21be9c86d7a7..07e9aac42163 100644
--- a/net/rxrpc/call_event.c
+++ b/net/rxrpc/call_event.c@@ -440,6 +440,19 @@ bool rxrpc_input_call_event(struct rxrpc_call *call) rxrpc_propose_ack_input_data); } + /* Need to rearm the RTO timer if we don't start the TLP-PTO + * timer [RFC8985 7.3]. + */ + if (call->rack_timer_mode == RXRPC_CALL_RACKTIMER_OFF && + rxrpc_tx_in_flight(call) > 0) { + ktime_t rto = rxrpc_get_rto_backoff(call, true); + + call->rack_timer_mode = RXRPC_CALL_RACKTIMER_RTO; + call->rack_timo_at = ktime_add(ktime_get_real(), rto); + trace_rxrpc_rack_timer(call, rto, false); + trace_rxrpc_timer_set(call, rto, rxrpc_timer_trace_rack_rto); + } + /* Make sure the timer is restarted */ if (!__rxrpc_call_is_complete(call)) { ktime_t next = READ_ONCE(call->expect_term_by), delay;
diff --git a/net/rxrpc/input.c b/net/rxrpc/input.c
index 73cafe6bfa9f..0e9f6a1e9f00 100644
--- a/net/rxrpc/input.c
+++ b/net/rxrpc/input.c@@ -34,6 +34,8 @@ static void rxrpc_congestion_management(struct rxrpc_call *call, { summary->change = rxrpc_cong_no_change; summary->in_flight = rxrpc_tx_in_flight(call); + call->cong_in_recovery = false; + call->cong_exiting_recovery = false; if (test_and_clear_bit(RXRPC_CALL_RETRANS_TIMEOUT, &call->flags)) { summary->retrans_timeo = true;
@@ -106,12 +108,12 @@ static void rxrpc_congestion_management(struct rxrpc_call *call, call->cong_extra = 0; call->cong_dup_acks = 0; summary->need_retransmit = true; - summary->in_fast_or_rto_recovery = true; + call->cong_in_recovery = true; + rxrpc_tlp_init(call); goto out; case RXRPC_CA_FAST_RETRANSMIT: - rxrpc_tlp_init(call); - summary->in_fast_or_rto_recovery = true; + call->cong_in_recovery = true; if (!summary->new_low_snack) { if (summary->nr_new_sacks == 0) call->cong_cwnd += 1;
@@ -125,7 +127,7 @@ static void rxrpc_congestion_management(struct rxrpc_call *call, summary->change = rxrpc_cong_progress; call->cong_cwnd = call->cong_ssthresh; if (call->acks_nr_snacks == 0) { - summary->exiting_fast_or_rto_recovery = true; + call->cong_exiting_recovery = true; goto resume_normality; } }
diff --git a/net/rxrpc/input_rack.c b/net/rxrpc/input_rack.c
index 072e1d9ecb2e..66ef2fc6d3d9 100644
--- a/net/rxrpc/input_rack.c
+++ b/net/rxrpc/input_rack.c@@ -29,7 +29,6 @@ static void rxrpc_rack_mark_lost(struct rxrpc_call *call, } else { call->tx_nr_lost++; } - tq->segment_xmit_ts[ix] = UINT_MAX; } /*
@@ -174,14 +173,14 @@ static ktime_t rxrpc_rack_update_reo_wnd(struct rxrpc_call *call, call->rack_dsack_round = snd_nxt; call->rack_reo_wnd_mult++; call->rack_reo_wnd_persist = 16; - } else if (summary->exiting_fast_or_rto_recovery) { + } else if (call->cong_exiting_recovery) { call->rack_reo_wnd_persist--; if (call->rack_reo_wnd_persist <= 0) call->rack_reo_wnd_mult = 1; } if (!call->rack_reordering_seen) { - if (summary->in_fast_or_rto_recovery) + if (call->cong_in_recovery) return 0; if (call->acks_nr_sacks >= dup_thresh) return 0;
@@ -227,6 +226,7 @@ static ktime_t rxrpc_rack_detect_loss(struct rxrpc_call *call, remaining = ktime_sub(ktime_add(xmit_ts, lost_after), now); if (remaining <= 0) { rxrpc_rack_mark_lost(call, tq, ix); + tq->segment_xmit_ts[ix] = UINT_MAX; trace_rxrpc_rack_detect_loss(call, summary, seq); } else { timeout = max(remaining, timeout);
@@ -297,7 +297,7 @@ ktime_t rxrpc_tlp_calc_pto(struct rxrpc_call *call, ktime_t now) if (call->rtt_count > 0) { /* Use 2*SRTT as the timeout. */ pto = ns_to_ktime(call->srtt_us * NSEC_PER_USEC / 4); - if (flight_size) + if (flight_size <= call->peer->pmtud_jumbo) pto = ktime_add(pto, call->tlp_max_ack_delay); } else { pto = NSEC_PER_SEC;
diff --git a/net/rxrpc/output.c b/net/rxrpc/output.c
index 88cad087f13b..9e082f740331 100644
--- a/net/rxrpc/output.c
+++ b/net/rxrpc/output.c@@ -576,8 +576,8 @@ static size_t rxrpc_prepare_data_packet(struct rxrpc_call *call, call->tx_nr_lost--; if (req->retrans) { __set_bit(ix, &tq->ever_retransmitted); - __set_bit(ix, &tq->segment_retransmitted); - call->tx_nr_resent++; + if (!__test_and_set_bit(ix, &tq->segment_retransmitted)) + call->tx_nr_resent++; } else { call->tx_nr_sent++; start_tlp = true;