From: Alexander Lobakin alobakin@dlink.ru
[ Upstream commit 8bef0af09a5415df761b04fa487a6c34acae74bc ]
Commit 43e665287f93 ("net-next: dsa: fix flow dissection") added an ability to override protocol and network offset during flow dissection for DSA-enabled devices (i.e. controllers shipped as switch CPU ports) in order to fix skb hashing for RPS on Rx path.
However, skb_hash() and added part of code can be invoked not only on Rx, but also on Tx path if we have a multi-queued device and: - kernel is running on UP system or - XPS is not configured.
The call stack in this two cases will be like: dev_queue_xmit() -> __dev_queue_xmit() -> netdev_core_pick_tx() -> netdev_pick_tx() -> skb_tx_hash() -> skb_get_hash().
The problem is that skbs queued for Tx have both network offset and correct protocol already set up even after inserting a CPU tag by DSA tagger, so calling tag_ops->flow_dissect() on this path actually only breaks flow dissection and hashing.
This can be observed by adding debug prints just before and right after tag_ops->flow_dissect() call to the related block of code:
Before the patch:
Rx path (RPS):
[ 19.240001] Rx: proto: 0x00f8, nhoff: 0 /* ETH_P_XDSA */ [ 19.244271] tag_ops->flow_dissect() [ 19.247811] Rx: proto: 0x0800, nhoff: 8 /* ETH_P_IP */
[ 19.215435] Rx: proto: 0x00f8, nhoff: 0 /* ETH_P_XDSA */ [ 19.219746] tag_ops->flow_dissect() [ 19.223241] Rx: proto: 0x0806, nhoff: 8 /* ETH_P_ARP */
[ 18.654057] Rx: proto: 0x00f8, nhoff: 0 /* ETH_P_XDSA */ [ 18.658332] tag_ops->flow_dissect() [ 18.661826] Rx: proto: 0x8100, nhoff: 8 /* ETH_P_8021Q */
Tx path (UP system):
[ 18.759560] Tx: proto: 0x0800, nhoff: 26 /* ETH_P_IP */ [ 18.763933] tag_ops->flow_dissect() [ 18.767485] Tx: proto: 0x920b, nhoff: 34 /* junk */
[ 22.800020] Tx: proto: 0x0806, nhoff: 26 /* ETH_P_ARP */ [ 22.804392] tag_ops->flow_dissect() [ 22.807921] Tx: proto: 0x920b, nhoff: 34 /* junk */
[ 16.898342] Tx: proto: 0x86dd, nhoff: 26 /* ETH_P_IPV6 */ [ 16.902705] tag_ops->flow_dissect() [ 16.906227] Tx: proto: 0x920b, nhoff: 34 /* junk */
After:
Rx path (RPS):
[ 16.520993] Rx: proto: 0x00f8, nhoff: 0 /* ETH_P_XDSA */ [ 16.525260] tag_ops->flow_dissect() [ 16.528808] Rx: proto: 0x0800, nhoff: 8 /* ETH_P_IP */
[ 15.484807] Rx: proto: 0x00f8, nhoff: 0 /* ETH_P_XDSA */ [ 15.490417] tag_ops->flow_dissect() [ 15.495223] Rx: proto: 0x0806, nhoff: 8 /* ETH_P_ARP */
[ 17.134621] Rx: proto: 0x00f8, nhoff: 0 /* ETH_P_XDSA */ [ 17.138895] tag_ops->flow_dissect() [ 17.142388] Rx: proto: 0x8100, nhoff: 8 /* ETH_P_8021Q */
Tx path (UP system):
[ 15.499558] Tx: proto: 0x0800, nhoff: 26 /* ETH_P_IP */
[ 20.664689] Tx: proto: 0x0806, nhoff: 26 /* ETH_P_ARP */
[ 18.565782] Tx: proto: 0x86dd, nhoff: 26 /* ETH_P_IPV6 */
In order to fix that we can add the check 'proto == htons(ETH_P_XDSA)' to prevent code from calling tag_ops->flow_dissect() on Tx. I also decided to initialize 'offset' variable so tagger callbacks can now safely leave it untouched without provoking a chaos.
Fixes: 43e665287f93 ("net-next: dsa: fix flow dissection") Signed-off-by: Alexander Lobakin alobakin@dlink.ru Reviewed-by: Florian Fainelli f.fainelli@gmail.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/core/flow_dissector.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
--- a/net/core/flow_dissector.c +++ b/net/core/flow_dissector.c @@ -450,9 +450,10 @@ bool __skb_flow_dissect(const struct sk_ nhoff = skb_network_offset(skb); hlen = skb_headlen(skb); #if IS_ENABLED(CONFIG_NET_DSA) - if (unlikely(skb->dev && netdev_uses_dsa(skb->dev))) { + if (unlikely(skb->dev && netdev_uses_dsa(skb->dev) && + proto == htons(ETH_P_XDSA))) { const struct dsa_device_ops *ops; - int offset; + int offset = 0;
ops = skb->dev->dsa_ptr->tag_ops; if (ops->flow_dissect &&