[4/4] net-next: dsa: fix flow dissection

Commit Message

John Crispin Aug. 9, 2017, 12:41 p.m. UTC

RPS and probably other kernel features are currently broken on some if not
all DSA devices. The root cause of this is that skb_hash will call the
flow_dissector. At this point the skb still contains the magic switch
header and the skb->protocol field is not set up to the correct 802.3
value yet. By the time the tag specific code is called, removing the header
and properly setting the protocol an invalid hash is already set. In the
case of the mt7530 this will result in all flows always having the same
hash.

Signed-off-by: Muciri Gatimu <[e-mail]>
Signed-off-by: Shashidhar Lakkavalli <[e-mail]>
Signed-off-by: John Crispin <[e-mail]>
---
 net/core/flow_dissector.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

Comments

Andrew Lunn Aug. 9, 2017, 1:55 p.m. UTC | #1

On Wed, Aug 09, 2017 at 02:41:19PM +0200, John Crispin wrote:
> RPS and probably other kernel features are currently broken on some if not
> all DSA devices. The root cause of this is that skb_hash will call the
> flow_dissector. At this point the skb still contains the magic switch
> header and the skb->protocol field is not set up to the correct 802.3
> value yet. By the time the tag specific code is called, removing the header
> and properly setting the protocol an invalid hash is already set. In the
> case of the mt7530 this will result in all flows always having the same
> hash.
> 
> Signed-off-by: Muciri Gatimu <[e-mail]>
> Signed-off-by: Shashidhar Lakkavalli <[e-mail]>
> Signed-off-by: John Crispin <[e-mail]>

Reviewed-by: Andrew Lunn <[e-mail]>

    Andrew

Patch

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index 0cc672aba1f0..5b5be9577257 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -4,6 +4,7 @@ 
 #include <linux/ip.h>
 #include <linux/ipv6.h>
 #include <linux/if_vlan.h>
+#include <net/dsa.h>
 #include <net/ip.h>
 #include <net/ipv6.h>
 #include <net/gre.h>
@@ -440,6 +441,17 @@  bool __skb_flow_dissect(const struct sk_buff *skb,
 			 skb->vlan_proto : skb->protocol;
 		nhoff = skb_network_offset(skb);
 		hlen = skb_headlen(skb);
+		if (unlikely(netdev_uses_dsa(skb->dev))) {
+			const struct dsa_device_ops *ops;
+			int offset;
+
+			ops = skb->dev->dsa_ptr->tag_ops;
+			if (ops->flow_dissect &&
+			    !ops->flow_dissect(skb, &proto, &offset)) {
+				hlen -= offset;
+				nhoff += offset;
+			}
+		}
 	}
 
 	/* It is ensured by skb_flow_dissector_init() that control key will