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Date: Fri, 06 Dec 2019 18:06:09 +0300 From: Alexander Lobakin <alobakin@...nk.ru> To: "David S. Miller" <davem@...emloft.net> Cc: Florian Fainelli <f.fainelli@...il.com>, Muciri Gatimu <muciri@...nmesh.com>, Shashidhar Lakkavalli <shashidhar.lakkavalli@...nmesh.com>, John Crispin <john@...ozen.org>, Andrew Lunn <andrew@...n.ch>, Vivien Didelot <vivien.didelot@...il.com>, Stanislav Fomichev <sdf@...gle.com>, Daniel Borkmann <daniel@...earbox.net>, Song Liu <songliubraving@...com>, Alexei Starovoitov <ast@...nel.org>, Matteo Croce <mcroce@...hat.com>, Jakub Sitnicki <jakub@...udflare.com>, Eric Dumazet <edumazet@...gle.com>, Paul Blakey <paulb@...lanox.com>, Yoshiki Komachi <komachi.yoshiki@...il.com>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH net] net: dsa: fix flow dissection on Tx path Florian Fainelli wrote 06.12.2019 06:28: > 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@...nk.ru> > > Reviewed-by: Florian Fainelli <f.fainelli@...il.com> So Dave, you can pick it up into your fixes tree if I understand correctly. There will be further work on DSA Rx path, but it's a subject for next Linux release cycles essentially. Regards, ᚷ ᛖ ᚢ ᚦ ᚠ ᚱ
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