FYI saw this on a system which was running 2.6.25rc5 for quite some time.
It might have been related to me restarting the NFS server (not 100% sure)
KERNEL: assertion (!sk->sk_forward_alloc) failed at /home/lsrc/misc/linux/net/ipv4/af_inet.c (157)
Happened only once so far.
-Andi