netdev - Re: [PATCH] pktgen: Clone skb to avoid corruption of skbs in ndo_start

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Message-ID: <1311105738.3113.11.camel@edumazet-laptop>
Date:	Tue, 19 Jul 2011 22:02:18 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Neil Horman <nhorman@...driver.com>
Cc:	netdev@...r.kernel.org, Alexey Dobriyan <adobriyan@...il.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] pktgen: Clone skb to avoid corruption of skbs in
 ndo_start_xmit methods

Le mardi 19 juillet 2011 à 15:52 -0400, Neil Horman a écrit :
> This oops was reported recently when running a pktgen script that called for a
> transmitted skb to be cloned and sent 100 times using the clone_skb command to a
> bridge device with several attached interface:
> 
...

> Turns out the pktgen driver doesn't actually clone skbs, but rather shares them,
> increasing the reference count of the skb for each send operation.  This works
> for most drivers because most drivers don't store or care about any state in the
> skb itself, but several do.  For instance, the above tun/tap driver and other
> soft drivers (vlans, bonding/bridging), all requeue frames to a physical device,
> meaning the skb next and prev pointers will be set.  Other drivers also care
> about skb state.  The virtio_net driver for instance uses the skb->cb space to
> store a vnet header and several converged adapters adjust the data pointer of an
> skb to prepend a device control header to the skb.  Drivers expect skbs
> submitted for i/o to be in their control and unshared with other users, an
> assumption which pktgen is violating, the result being multiple skb users
> corrupting one antohers state and producing oopses like the one above.  The
> solution is to make pktgen clone the skb for each transmit so as to ensure the
> drivers assumptions about private exclusive access to the skb is maintained.
> 
> Tested successfully by myself
> Signed-off-by: Neil Horman <nhorman@...driver.com>
> Reported-by: Jiri Pirko <jpirko@...hat.com>
> CC: Eric Dumazet <eric.dumazet@...il.com>
> CC: Alexey Dobriyan <adobriyan@...il.com>
> CC: David S. Miller <davem@...emloft.net>
> ---

This will kill pktgen performance ?

pktgen is only for sysadmins, and very skilled ones :)

BTW you forgot to CC pktgen author, Robert Olsson



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