Is anyone else using NFS? I think I found the cause of my hanging when I boot with the 3.4.0-1 kernel.
I think it might have been trying to mount NFS volumes before networking had started.
May 4 11:45:14 saturn kernel: [ 7.434856] Installing knfsd (copyright (C) 1996 okir@monad.swb.de).
May 4 11:45:14 saturn kernel: [ 7.438160] BUG: unable to handle kernel NULL pointer dereference at (null)
May 4 11:45:14 saturn kernel: [ 7.438164] IP: [<ffffffffa10d01ae>] rpc_pipefs_event+0xae/0x220 [nfs]
May 4 11:45:14 saturn kernel: [ 7.438175] PGD 31b704067 PUD 3101d7067 PMD 0
May 4 11:45:14 saturn kernel: [ 7.438177] Oops: 0000 [#1] SMP
May 4 11:45:14 saturn kernel: [ 7.438179] CPU 8
...
May 4 11:45:14 saturn kernel: [ 7.946858] ADDRCONF(NETDEV_UP): eth0: link is not ready
May 4 11:45:14 saturn kernel: [ 7.947030] ADDRCONF(NETDEV_UP): eth0: link is not ready
May 4 11:45:16 saturn kernel: [ 9.533966] e1000e: eth0 NIC Link is Up 100 Mbps Full Duplex, Flow Control: None
May 4 11:45:16 saturn kernel: [ 9.533970] e1000e 0000:00:19.0: eth0: 10/100 speed: disabling TSO
May 4 11:45:16 saturn kernel: [ 9.534964] ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
May 4 11:45:26 saturn kernel: [ 20.208857] eth0: no IPv6 routers present
May 4 11:46:41 saturn kernel: [ 96.142650] BUG: soft lockup - CPU#0 stuck for 22s! [mount.nfs:1361]
I guess I'm off to see if anyone's reported this on launchpad.