[PATCH 6.12 330/337] rxrpc: Fix the calculation and use of RTO

[Greg Kroah-Hartman]

6.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Howells <dhowells at redhat.com>

[ Upstream commit 5c0ceba23bb47085d6c9c53bff08a29634ee4e7e ]

Make the following changes to the calculation and use of RTO:

 (1) Fix rxrpc_resend() to use the backed-off RTO value obtained by calling
     rxrpc_get_rto_backoff() rather than extracting the value itself.
     Without this, it may retransmit packets too early.

 (2) The RTO value being similar to the RTT causes a lot of extraneous
     resends because the RTT doesn't end up taking account of clearing out
     of the receive queue on the server.  Worse, responses to PING-ACKs are
     made as fast as possible and so are less than the DATA-requested-ACK
     RTT and so skew the RTT down.

     Fix this by putting a lower bound on the RTO by adding 100ms to it and
     limiting the lower end to 200ms.

Fixes: c410bf01933e ("rxrpc: Fix the excessive initial retransmission timeout")
Fixes: 37473e416234 ("rxrpc: Clean up the resend algorithm")
Signed-off-by: David Howells <dhowells at redhat.com>
Suggested-by: Simon Wilkinson <sxw at auristor.com>
cc: Marc Dionne <marc.dionne at auristor.com>
cc: linux-afs at lists.infradead.org
Signed-off-by: Jakub Kicinski <kuba at kernel.org>
Stable-dep-of: e4d2878369d5 ("rxrpc: Fix irq-disabled in local_bh_enable()")
Signed-off-by: Sasha Levin <sashal at kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
 net/rxrpc/call_event.c |    3 ++-
 net/rxrpc/rtt.c        |    2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

--- a/net/rxrpc/call_event.c
+++ b/net/rxrpc/call_event.c
@@ -71,7 +71,8 @@ void rxrpc_resend(struct rxrpc_call *cal
 	struct rxrpc_skb_priv *sp;
 	struct rxrpc_txbuf *txb;
 	rxrpc_seq_t transmitted = call->tx_transmitted;
-	ktime_t next_resend = KTIME_MAX, rto = ns_to_ktime(call->peer->rto_us * NSEC_PER_USEC);
+	ktime_t next_resend = KTIME_MAX;
+	ktime_t rto = rxrpc_get_rto_backoff(call->peer, false);
 	ktime_t resend_at = KTIME_MAX, now, delay;
 	bool unacked = false, did_send = false;
 	unsigned int i;
--- a/net/rxrpc/rtt.c
+++ b/net/rxrpc/rtt.c
@@ -27,7 +27,7 @@ static u32 __rxrpc_set_rto(const struct
 
 static u32 rxrpc_bound_rto(u32 rto)
 {
-	return min(rto, RXRPC_RTO_MAX);
+	return clamp(200000, rto + 100000, RXRPC_RTO_MAX);
 }
 
 /*