Re: [PATCH v4 net-next] net: introduce dev_set_forwarding()

[Christoph Paasch <christoph.paasch@uclouvain.be>]

On 02/11/13 - 12:58:50, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> Christoph Paasch and Jerry Chu reported crashes in skb_segment() caused
> by commit 8a29111c7ca6 ("net: gro: allow to build full sized skb")
> 
> skb_segment() only deals with a frag_list chain containing MSS sized
> fragments. Even if we fix this problem, its better if GRO layer
> doesn't build skb with a frag_list in the first place, to let TSO
> packets reaching output devices.
>  
> David Miller and Ben Hutchings suggested we keep track of number of
> forwarding users to be able to :
> 
> - Disable LRO
> - Make sure GRO layer do not use skb frag_list to extend skb capacity
> 
> Note that after this patch, LRO is automatically re-enabled if
> forwarding is disabled on the device, or if a device is removed
> from a bridge.
> 
> Tested:
> 
> lpq84:~# ethtool -k eth0 | grep "large-receive"
> large-receive-offload: on
> lpq84:~# echo 1 >/proc/sys/net/ipv4/conf/eth0/forwarding
> lpq84:~# ethtool -k eth0 | grep "large-receive"
> large-receive-offload: off [requested on]
> lpq84:~# echo 0 >/proc/sys/net/ipv4/conf/eth0/forwarding
> lpq84:~# ethtool -k eth0 | grep "large-receive"
> large-receive-offload: on
> 
> 
> lpq84:~# ethtool -K eth0 lro off
> lpq84:~# ethtool -k eth0 | grep "large-receive"
> large-receive-offload: off
> lpq84:~# echo 1 >/proc/sys/net/ipv4/conf/eth0/forwarding
> lpq84:~# ethtool -k eth0 | grep "large-receive"
> large-receive-offload: off
> lpq84:~# echo 0 >/proc/sys/net/ipv4/conf/eth0/forwarding
> lpq84:~# ethtool -k eth0 | grep "large-receive"
> large-receive-offload: off
> lpq84:~# ethtool -K eth0 lro on 
> 
> 
> lpq84:~# cat /proc/sys/net/ipv4/ip_forward
> 0
> lpq84:~# echo 1 >/proc/sys/net/ipv4/ip_forward
> lpq84:~# ethtool -k eth0 | grep "large-receive"
> large-receive-offload: off [requested on]
> lpq84:~# echo 0 >/proc/sys/net/ipv4/ip_forward
> lpq84:~# ethtool -k eth0 | grep "large-receive"
> large-receive-offload: on
> 
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Reported-by: Christoph Paasch <christoph.paasch@uclouvain.be>
> Reported-by: Jerry Chu <hkchu@google.com>
> Cc: Michael Dalton <mwdalton@google.com>
> Fixes: 8a29111c7ca6 ("net: gro: allow to build full sized skb")
> ---
> v4: drop LRO in netdev_fix_features(), ase Ben pointed out.
> 
>  include/linux/netdevice.h |    3 ++-
>  net/bridge/br_if.c        |    4 +++-
>  net/core/dev.c            |   31 ++++++++++++++++++++-----------
>  net/core/skbuff.c         |   11 ++++++++---
>  net/ipv4/devinet.c        |   14 ++++++++------
>  net/ipv6/addrconf.c       |    5 ++---
>  net/ipv6/addrconf_core.c  |    2 ++
>  7 files changed, 45 insertions(+), 25 deletions(-)

Good, this fixes the crash I experienced on my workload.

Tested-by: Christoph Paasch <christoph.paasch@uclouvain.be>

Thanks, Eric!