linux-kernel - Re: [PATCH net V3 2/2] net: core: explicitly select a txq before doing l2 forwarding

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Message-Id: <20140110.132428.2182820842932734377.davem@davemloft.net>
Date:	Fri, 10 Jan 2014 13:24:28 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	jasowang@...hat.com
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	mst@...hat.com, john.r.fastabend@...el.com, nhorman@...driver.com,
	e1000-devel@...ts.sourceforge.net
Subject: Re: [PATCH net V3 2/2] net: core: explicitly select a txq before
 doing l2 forwarding

From: Jason Wang <jasowang@...hat.com>
Date: Fri, 10 Jan 2014 16:18:26 +0800

> Currently, the tx queue were selected implicitly in ndo_dfwd_start_xmit(). The
> will cause several issues:
> 
> - NETIF_F_LLTX were removed for macvlan, so txq lock were done for macvlan
>   instead of lower device which misses the necessary txq synchronization for
>   lower device such as txq stopping or frozen required by dev watchdog or
>   control path.
> - dev_hard_start_xmit() was called with NULL txq which bypasses the net device
>   watchdog.
> - dev_hard_start_xmit() does not check txq everywhere which will lead a crash
>   when tso is disabled for lower device.
> 
> Fix this by explicitly introducing a new param for .ndo_select_queue() for just
> selecting queues in the case of l2 forwarding offload. netdev_pick_tx() was also
> extended to accept this parameter and dev_queue_xmit_accel() was used to do l2
> forwarding transmission.
> 
> With this fixes, NETIF_F_LLTX could be preserved for macvlan and there's no need
> to check txq against NULL in dev_hard_start_xmit(). Also there's no need to keep
> a dedicated ndo_dfwd_start_xmit() and we can just reuse the code of
> dev_queue_xmit() to do the transmission.
> 
> In the future, it was also required for macvtap l2 forwarding support since it
> provides a necessary synchronization method.
> 
> Cc: John Fastabend <john.r.fastabend@...el.com>
> Cc: Neil Horman <nhorman@...driver.com>
> Cc: e1000-devel@...ts.sourceforge.net
> Signed-off-by: Jason Wang <jasowang@...hat.com>

Applied.
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