Messages in this thread | | | Subject | Re: [PATCH net] net: dsa: fix flow dissection on Tx path | From | Florian Fainelli <> | Date | Thu, 5 Dec 2019 19:28:32 -0800 |
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On 12/5/2019 2:02 AM, Alexander Lobakin wrote: > 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> -- Florian
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