linux-kernel - [PATCH net 3/3] rxrpc: Fix afs large storage transmission performance drop

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Message-ID: <159246663560.1229328.1476552302291944463.stgit@warthog.procyon.org.uk>
Date:   Thu, 18 Jun 2020 08:50:35 +0100
From:   David Howells <dhowells@...hat.com>
To:     netdev@...r.kernel.org
Cc:     dhowells@...hat.com, linux-afs@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH net 3/3] rxrpc: Fix afs large storage transmission performance
 drop

Commit 2ad6691d988c, which moved the modification of the status annotation
for a packet in the Tx buffer prior to the retransmission moved the state
clearance, but managed to lose the bit that set it to UNACK.

Consequently, if a retransmission occurs, the packet is accidentally
changed to the ACK state (ie. 0) by masking it off, which means that the
packet isn't counted towards the tally of newly-ACK'd packets if it gets
hard-ACK'd.  This then prevents the congestion control algorithm from
recovering properly.

Fix by reinstating the change of state to UNACK.

Spotted by the generic/460 xfstest.

Fixes: 2ad6691d988c ("rxrpc: Fix race between incoming ACK parser and retransmitter")
Signed-off-by: David Howells <dhowells@...hat.com>
---

 net/rxrpc/call_event.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/rxrpc/call_event.c b/net/rxrpc/call_event.c
index aa1c8eee6557..6be2672a65ea 100644
--- a/net/rxrpc/call_event.c
+++ b/net/rxrpc/call_event.c
@@ -253,7 +253,7 @@ static void rxrpc_resend(struct rxrpc_call *call, unsigned long now_j)
 		 * confuse things
 		 */
 		annotation &= ~RXRPC_TX_ANNO_MASK;
-		annotation |= RXRPC_TX_ANNO_RESENT;
+		annotation |= RXRPC_TX_ANNO_UNACK | RXRPC_TX_ANNO_RESENT;
 		call->rxtx_annotations[ix] = annotation;

 		skb = call->rxtx_buffer[ix];