Re: [PATCH] pktgen: Clone skb to avoid corruption of skbs in ndo_start_xmit methods

Eric Dumazet
2011-07-19T20:02:23Z

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@tuxdriver.com>
> Reported-by: Jiri Pirko <jpirko@redhat.com>
> CC: Eric Dumazet <eric.dumazet@gmail.com>
> CC: Alexey Dobriyan <adobriyan@gmail.com>
> CC: David S. Miller <davem@davemloft.net>
> ---

This will kill pktgen performance ?

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

BTW you forgot to CC pktgen author, Robert Olsson