[PATCH net v2 3/3] rxrpc: Fix RACK-TLP implementation
David Howells
dhowells at redhat.com
Tue Oct 20 13:12:54 PDT 2026
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 at redhat.com>
Reviewed-by: Marc Dionne <marc.dionne at auristor.com>
Tested-by: Marc Dionne <marc.dionne at auristor.com>
Reviewed-by: Jeffrey Altman <jaltman at auristor.com>
cc: Eric Dumazet <edumazet at google.com>
cc: "David S. Miller" <davem at davemloft.net>
cc: Jakub Kicinski <kuba at kernel.org>
cc: Paolo Abeni <pabeni at redhat.com>
cc: Simon Horman <horms at kernel.org>
cc: linux-afs at lists.infradead.org
cc: stable at vger.kernel.org
---
net/rxrpc/ar-internal.h | 2 +-
net/rxrpc/call_event.c | 13 +++++++++++++
net/rxrpc/input.c | 7 ++++---
net/rxrpc/input_rack.c | 6 +++---
4 files changed, 21 insertions(+), 7 deletions(-)
diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index d0e18eb6301e..d3b1b095192d 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -811,6 +811,7 @@ struct rxrpc_call {
#define RXRPC_TX_SMSS RXRPC_JUMBO_DATALEN
#define RXRPC_MIN_CWND 4
enum rxrpc_ca_state cong_ca_state; /* Congestion control state */
+ bool cong_in_recovery:1; /* If we're in Fast/RTO recovery */
u8 cong_extra; /* Extra to send for congestion management */
u16 cong_cwnd; /* Congestion window size */
u16 cong_ssthresh; /* Slow-start threshold */
@@ -895,7 +896,6 @@ 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..f83db83df89d 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 &&
+ call->tx_in_flight > 0) {
+ ktime_t rto = rxrpc_get_rto_backoff(call, false);
+
+ 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 f497eba59cf6..815749c7abeb 100644
--- a/net/rxrpc/input.c
+++ b/net/rxrpc/input.c
@@ -34,6 +34,7 @@ static void rxrpc_congestion_management(struct rxrpc_call *call,
{
summary->change = rxrpc_cong_no_change;
summary->in_flight = call->tx_in_flight;
+ call->cong_in_recovery = false;
if (test_and_clear_bit(RXRPC_CALL_RETRANS_TIMEOUT, &call->flags)) {
summary->retrans_timeo = true;
@@ -106,12 +107,12 @@ 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;
diff --git a/net/rxrpc/input_rack.c b/net/rxrpc/input_rack.c
index e43ce032a261..1f6b51fa9721 100644
--- a/net/rxrpc/input_rack.c
+++ b/net/rxrpc/input_rack.c
@@ -30,7 +30,6 @@ static void rxrpc_rack_mark_lost(struct rxrpc_call *call,
if (__test_and_clear_bit(ix, &tq->in_flight))
call->tx_in_flight--;
- tq->segment_xmit_ts[ix] = UINT_MAX;
}
/*
@@ -184,7 +183,7 @@ static ktime_t rxrpc_rack_update_reo_wnd(struct rxrpc_call *call,
}
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;
@@ -230,6 +229,7 @@ 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);
@@ -300,7 +300,7 @@ 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 <= max(call->peer->pmtud_jumbo, 1))
pto = ktime_add(pto, call->tlp_max_ack_delay);
} else {
pto = NSEC_PER_SEC;
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