Re: multiple local nodes (patch)

To: Daniel Drown <dan-lvs@xxxxxxxxx>
Subject: Re: multiple local nodes (patch)
Cc: lvs-devel@xxxxxxxxxxxxxxx
From: Simon Horman <horms@xxxxxxxxxxxx>
Date: Wed, 24 Dec 2008 14:51:18 +1100
On Mon, Dec 08, 2008 at 09:40:12PM +0000, Daniel Drown wrote:
> I have a need for multiple local nodes in LVS.  I started from the patch from
> 2005:
> I found three problems with it:
> 1. packet checksums were not calculated correctly
> 2. having stats enabled would deadlock the kernel in the stats update function
>       (ip_vs_in_stats/ip_vs_out_stats)
> 3. the kernel would deadlock in the packet recieve function (ip_vs_in)
> For #1, I believe this was because the existing code assumes the TCP/UDP
> checksums are correct (which is not true for locally generated packets with
> hardware checksum).  I just used the same code that the tcp and udp functions
> use.
> For #2 and #3, the problem was that the majority of the code runs as a bottom
> handler.  Locally generated packets are run as a normal kernel context.  If a
> network interrupt happens while the kernel is holding a IPVS lock for sending
> a local packet, it can schedule the bottom handler.  The bottom handler can
> then try to acquire the same lock, and this is a deadlock.  To prevent this
> from happening, I've disabled bottom handlers (local_bh_disable) in the local
> packet output function I created (ip_vs_out_nobh).
> I've tested this and it works on a RH5/CentOS5 kernel:
> I've ported it to a stock kernel, but I haven't had time to test it
> out yet:
> I welcome any comments or criticism on the code.

Hi Daniel,

sorry to take so long to respond, I have been meaning to do so.

Your patch seems good to me (though I am somewhat biases as I wrote
the patch you based your patch on). Would it be possible for you to

a) update the code to either DaveM's net-next-2.6 tree on,
   or at the very least one of the 2.6.29-rc releases? In particular
   please note that the lvs code has moved from net/ipv4/ipvs/ to
   net/netfilter/ipvs/ . Also, I think that you will need to rework
   your checksum code changes a little to accomodate IPv6, which
   has been merged into IPVS recently.

b) Provide a Signed-off-by line, an explanation of which can be found at

Simon Horman
  VA Linux Systems Japan K.K., Sydney, Australia Satellite Office
  H:             W:

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