Messages in this thread | | | From | Rainer Sickinger <> | Date | Fri, 6 Dec 2019 20:32:29 +0100 | Subject | Re: [PATCH net] net: dsa: fix flow dissection on Tx path |
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That is a really great improvement!
Am Do., 5. Dez. 2019 um 11:04 Uhr schrieb Alexander Lobakin <alobakin@dlink.ru>: > > 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> > --- > net/core/flow_dissector.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c > index 69395b804709..d524a693e00f 100644 > --- a/net/core/flow_dissector.c > +++ b/net/core/flow_dissector.c > @@ -969,9 +969,10 @@ bool __skb_flow_dissect(const struct net *net, > 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 && > -- > 2.24.0 >
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