I've been getting something similar when changing network connections while having nfs stuff mounted:


[27025.825196] ------------[ cut here ]------------                                                                                                           
[27025.825206] kernel BUG at /build/buildd/linux-2.6.27/net/sunrpc/rpcb_clnt.c:498!                                                                           
[27025.825212] invalid opcode: 0000 [#10] SMP                                                                                                                 
[27025.825218] Modules linked in: aes_i586 crypto_blkcipher aes_generic ieee80211_crypt_ccmp ipv6 af_packet binfmt_misc rfcomm bridge stp bnep sco l2cap bluetooth ppdev acpi_cpufreq cpufreq_powersave cpufreq_stats cpufreq_userspace cpufreq_ondemand cpufreq_conservative freq_table container sbs pci_slot sbshc nfs lockd nfs_acl sunrpc iptable_filter ip_tables x_tables ext3 jbd mbcache eeprom i2c_i801 i2c_core parport_pc lp parport joydev pcmcia led_class wmi psmouse serio_raw pcspkr evdev snd_hda_intel snd_pcm_oss snd_mixer_oss snd_pcm snd_seq_dummy video ipw2200 output ieee80211 ieee80211_crypt yenta_socket rsrc_nonstatic pcmcia_core snd_seq_oss fglrx(P) snd_seq_midi snd_rawmidi battery snd_seq_midi_event snd_seq ac button snd_timer snd_seq_device iTCO_wdt iTCO_vendor_support snd soundcore snd_page_alloc shpchp pci_hotplug intel_agp agpgart reiserfs usbhid hid sr_mod cdrom sd_mod crc_t10dif sg ata_piix ata_generic 8139cp pata_acpi libata 8139too mii scsi_mod dock ehci_hcd uhci_hcd usbcore thermal processor fan fbcon tileblit font bitblit softcursor fuse                                      
[27025.825378]                                                                                                                                                
[27025.825384] Pid: 18298, comm: mount.nfs Tainted: P      D   (2.6.27-9-generic #1)                                                                          
[27025.825390] EIP: 0060:[<f909a5c8>] EFLAGS: 00010287 CPU: 0                                                                                                 
[27025.825428] EIP is at rpcb_getport_async+0x478/0x4e0 [sunrpc]                                                                                              
[27025.825433] EAX: c2548840 EBX: eaf0ea00 ECX: eaf0e200 EDX: f90b4920                                                                                        
[27025.825438] ESI: d50f8000 EDI: 00000000 EBP: c26e9ca8 ESP: c26e9bbc                                                                                        
[27025.825443]  DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068                                                                                                  
[27025.825449] Process mount.nfs (pid: 18298, ti=c26e8000 task=dd503240 task.ti=c26e8000)                                                                     
[27025.825454] Stack: 00000000 00000046 714c9ccf 00001894 f750f110 c26e9bf0 c012a571 c2548840                                                                 
[27025.825468]        eaf0e200 c190cd00 dd503240 f750f110 c26e9c14 c0102df6 dd50357c c190a980                                                                 
[27025.825481]        c26e9c1c c190cd00 c26e9c1c c037e935 00000001 c190cd00 dd503240 f750f110                                                                 
[27025.825494] Call Trace:                                                                                                                                    
[27025.825499]  [<c012a571>] ? hrtick_start_fair+0x181/0x1a0                                                                                                  
[27025.825512]  [<c0102df6>] ? __switch_to+0xa6/0x160                                                                                                         
[27025.825520]  [<c037e935>] ? __reacquire_kernel_lock+0x15/0x70                                                                                              
[27025.825530]  [<c0187063>] ? mempool_alloc_slab+0x13/0x20
[27025.825539]  [<c0187345>] ? mempool_alloc+0x35/0xf0
[27025.825550]  [<f90928be>] ? rpc_malloc+0x3e/0xa0 [sunrpc]
[27025.825581]  [<c037e6dd>] ? _spin_lock+0xd/0x10
[27025.825592]  [<f908de3c>] ? xprt_reserve+0x4c/0x1a0 [sunrpc]
[27025.825637]  [<f908d43a>] ? call_bind+0x4a/0x80 [sunrpc]
[27025.825669]  [<f908b305>] ? call_reserve+0x45/0x80 [sunrpc]
[27025.825698]  [<f909365a>] ? __rpc_execute+0x5a/0x250 [sunrpc]
[27025.825730]  [<f90938c9>] ? rpc_execute+0x79/0x90 [sunrpc]
[27025.825775]  [<f908c743>] ? rpc_run_task+0x33/0x70 [sunrpc]
[27025.825806]  [<f908c8a0>] ? rpc_call_sync+0x40/0x70 [sunrpc]
[27025.825850]  [<f908c918>] ? rpc_ping+0x48/0x60 [sunrpc]
[27025.825901]  [<f908ce06>] ? rpc_bind_new_program+0x66/0x90 [sunrpc]
[27025.825932]  [<f91175d7>] ? nfs_init_server+0x3a7/0x440 [nfs]
[27025.825977]  [<f91176a5>] ? nfs_create_server+0x35/0x2a0 [nfs]
[27025.826003]  [<f911f0e7>] ? nfs_parse_ip_address+0xc7/0x120 [nfs]
[27025.826053]  [<f911fe7f>] ? nfs_try_mount+0x9f/0x120 [nfs]
[27025.826081]  [<f91203ad>] ? nfs_validate_mount_data+0x4ad/0x550 [nfs]
[27025.826109]  [<f91203ad>] ? nfs_validate_mount_data+0x4ad/0x550 [nfs]
[27025.826136]  [<f91221e9>] ? nfs_get_sb+0x99/0x300 [nfs]
[27025.826180]  [<c01b43ee>] ? vfs_kern_mount+0x5e/0x130
[27025.826195]  [<c01b451e>] ? do_kern_mount+0x3e/0xe0
[27025.826203]  [<c01cc9ef>] ? do_new_mount+0x6f/0x90
[27025.826212]  [<c01ccf32>] ? do_mount+0x1d2/0x1f0
[27025.826220]  [<c01ca67d>] ? exact_copy_from_user+0x4d/0xa0
[27025.826228]  [<c01cac8e>] ? copy_mount_options+0x6e/0xd0
[27025.826236]  [<c01ccfe1>] ? sys_mount+0x91/0xc0
[27025.826244]  [<c0103f7b>] ? sysenter_do_call+0x12/0x2f
[27025.826252]  =======================
[27025.826255] Code: c7 44 24 08 80 22 0a f9 0f b7 81 86 00 00 00 c7 04 24 dc 57 0a f9 89 44 24 04 e8 dd 1e 2e c7 e9 13 fc ff ff 8d b4 26 00 00 00 00 <0f> 0beb fe 8b 8d 30 ff ff ff c7 44 24 08 80 22 0a f9 0f b7 81
[27025.826326] EIP: [<f909a5c8>] rpcb_getport_async+0x478/0x4e0 [sunrpc] SS:ESP 0068:c26e9bbc
[27025.826432] ---[ end trace a4de1416d7fbb9c2 ]---