netdev - [PATCH net-next] net: flow_dissector: fix RPS on DSA masters

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Message-Id: <20210614135819.504455-1-olteanv@gmail.com>
Date:   Mon, 14 Jun 2021 16:58:19 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: [PATCH net-next] net: flow_dissector: fix RPS on DSA masters

From: Vladimir Oltean <vladimir.oltean@....com>

After the blamed patch, __skb_flow_dissect() on the DSA master stopped
adjusting for the length of the DSA headers. This is because it was told
to adjust only if the needed_headroom is zero, aka if there is no DSA
header. Of course, the adjustment should be done only if there _is_ a
DSA header.

Modify the comment too so it is clearer.

Fixes: 4e50025129ef ("net: dsa: generalize overhead for taggers that use both headers and trailers")
Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 net/core/flow_dissector.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index c04455981c1e..2aadbfc5193b 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -943,8 +943,8 @@ bool __skb_flow_dissect(const struct net *net,
 			int offset = 0;
 
 			ops = skb->dev->dsa_ptr->tag_ops;
-			/* Tail taggers don't break flow dissection */
-			if (!ops->needed_headroom) {
+			/* Only DSA header taggers break flow dissection */
+			if (ops->needed_headroom) {
 				if (ops->flow_dissect)
 					ops->flow_dissect(skb, &proto, &offset);
 				else
-- 
2.25.1