netdev - [RFC PATCH 27/28] gro: flushing when CWR is set negatively affects AccECN

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Date:   Wed, 18 Mar 2020 11:38:08 +0200
From:   Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
To:     netdev@...r.kernel.org
Cc:     Yuchung Cheng <ycheng@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Olivier Tilmans <olivier.tilmans@...ia-bell-labs.com>
Subject: [RFC PATCH 27/28] gro: flushing when CWR is set negatively affects AccECN

From: Ilpo Järvinen <ilpo.jarvinen@...helsinki.fi>

As AccECN may keep CWR bit asserted due to different
interpretation of the bit, flushing with GRO because of
CWR may effectively disable GRO until AccECN counter
field changes such that CWR-bit becomes 0.

There is no harm done from not immediately forwarding the
CWR'ed segment with RFC3168 ECN.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...helsinki.fi>
---
 net/ipv4/tcp_offload.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
index 58ce382c793e..555c9be84f10 100644
--- a/net/ipv4/tcp_offload.c
+++ b/net/ipv4/tcp_offload.c
@@ -240,7 +240,6 @@ struct sk_buff *tcp_gro_receive(struct list_head *head, struct sk_buff *skb)
 found:
 	/* Include the IP ID check below from the inner most IP hdr */
 	flush = NAPI_GRO_CB(p)->flush;
-	flush |= (__force int)(flags & TCP_FLAG_CWR);
 	flush |= (__force int)((flags ^ tcp_flag_word(th2)) &
 		  ~(TCP_FLAG_FIN | TCP_FLAG_PSH));
 	flush |= (__force int)(th->ack_seq ^ th2->ack_seq);
-- 
2.20.1