From: David Miller <davem@davemloft.net>
To: alobakin@dlink.ru
Cc: muciri@openmesh.com, shashidhar.lakkavalli@openmesh.com,
john@phrozen.org, andrew@lunn.ch, vivien.didelot@gmail.com,
f.fainelli@gmail.com, sdf@google.com, daniel@iogearbox.net,
songliubraving@fb.com, ast@kernel.org, mcroce@redhat.com,
jakub@cloudflare.com, edumazet@google.com, paulb@mellanox.com,
komachi.yoshiki@gmail.com, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH net] net: dsa: fix flow dissection on Tx path
Date: Fri, 06 Dec 2019 20:19:50 -0800 (PST) [thread overview]
Message-ID: <20191206.201950.100960973648804142.davem@davemloft.net> (raw)
In-Reply-To: <20191205100235.14195-1-alobakin@dlink.ru>
From: Alexander Lobakin <alobakin@dlink.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@dlink.ru>
Applied and queued up for -stable.
next prev parent reply other threads:[~2019-12-07 4:19 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-05 10:02 [PATCH net] net: dsa: fix flow dissection on Tx path Alexander Lobakin
2019-12-05 12:58 ` Andrew Lunn
2019-12-05 13:34 ` Alexander Lobakin
2019-12-05 14:01 ` Andrew Lunn
2019-12-05 14:58 ` Alexander Lobakin
2019-12-06 3:32 ` Florian Fainelli
2019-12-06 7:37 ` Alexander Lobakin
2019-12-06 18:05 ` Florian Fainelli
2019-12-06 3:28 ` Florian Fainelli
2019-12-06 15:06 ` Alexander Lobakin
2019-12-06 19:32 ` Rainer Sickinger
2019-12-07 4:19 ` David Miller [this message]
2019-12-07 8:10 ` Alexander Lobakin
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