netdev - [PATCH net-next] mpls: Do not orphan the skb

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Message-id: <20240306181117.77419-1-cpaasch@apple.com>
Date: Wed, 06 Mar 2024 10:11:17 -0800
From: Christoph Paasch <cpaasch@...le.com>
To: David Miller <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, Roopa Prabhu <roopa@...dia.com>,
 Craig Taylor <cmtaylor@...le.com>
Subject: [PATCH net-next] mpls: Do not orphan the skb

We observed that TCP-pacing was falling back to the TCP-layer pacing
instead of utilizing sch_fq for the pacing. This causes significant
CPU-usage due to the hrtimer running on a per-TCP-connection basis.

The issue is that mpls_xmit() calls skb_orphan() and thus sets
skb->sk to NULL. Which implies that many of the goodies of TCP won't
work. Pacing falls back to TCP-layer pacing. TCP Small Queues does not
work, ...

It is safe to remove this call to skb_orphan() in mpls_xmit() as there
really is not reason for it to be there. It appears that this call to
skb_orphan comes from the very initial implementation of MPLS.

Cc: Roopa Prabhu <roopa@...dia.com>
Reported-by: Craig Taylor <cmtaylor@...le.com>
Signed-off-by: Christoph Paasch <cpaasch@...le.com>
---
 net/mpls/mpls_iptunnel.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/net/mpls/mpls_iptunnel.c b/net/mpls/mpls_iptunnel.c
index ef59e25dc482..8fc790f2a01b 100644
--- a/net/mpls/mpls_iptunnel.c
+++ b/net/mpls/mpls_iptunnel.c
@@ -55,8 +55,6 @@ static int mpls_xmit(struct sk_buff *skb)
 	out_dev = dst->dev;
 	net = dev_net(out_dev);

-	skb_orphan(skb);
-
 	if (!mpls_output_possible(out_dev) ||
 	    !dst->lwtstate || skb_warn_if_lro(skb))
 		goto drop;
-- 
2.39.3 (Apple Git-146)