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I have a need for multiple local nodes in LVS. I started from the patch from
2005:
http://archive.linuxvirtualserver.org/html/lvs-users/2005-06/msg00113.html
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 2.6.18.92.1.17.el5 kernel:
http://dan.drown.org/software/ipvs-2.6.18-92.1.17.el5-multiple-local-nodes.patch
I've ported it to a stock 2.6.27.7 kernel, but I haven't had time to test it
out yet:
http://dan.drown.org/software/ipvs-2.6.27.7-multiple-local-nodes.patch
I welcome any comments or criticism on the code.
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