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Message-Id: <20191206.201950.100960973648804142.davem@davemloft.net> Date: Fri, 06 Dec 2019 20:19:50 -0800 (PST) From: David Miller <davem@...emloft.net> To: alobakin@...nk.ru Cc: muciri@...nmesh.com, shashidhar.lakkavalli@...nmesh.com, john@...ozen.org, andrew@...n.ch, vivien.didelot@...il.com, f.fainelli@...il.com, sdf@...gle.com, daniel@...earbox.net, songliubraving@...com, ast@...nel.org, mcroce@...hat.com, jakub@...udflare.com, edumazet@...gle.com, paulb@...lanox.com, 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 From: Alexander Lobakin <alobakin@...nk.ru> Date: Thu, 5 Dec 2019 13:02:35 +0300 > 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: ... > 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> Applied and queued up for -stable.
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