I've just been shot-down by this bug again! Kernel is '2.6.24-23-server' (ubuntu-server 8.04.2 hardy LTS x86-64).

Guys, we badly need to bury this hatchet - this appears to be the only bug preventing LTS release being a solid fileserver.

The Linux NFS maintainer squarely cited this patch to fix this failure:
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git&a=commitdiff&h=9a4bd29fe8f6d3f015fe1c8e5450eb62cfebfcc9

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kernel BUG at /build/buildd/linux-2.6.24/net/sunrpc/rpcb_clnt.c:322!
invalid opcode: 0000 [1] SMP 
CPU 1 
Modules linked in: eip ep elan4 elan qsnet myri10ge dca inet_lro tcp_cubic af_packet nfsd auth_rpcgss exportfs acpi_cpufreq cpufreq_powersave cpufreq_ondemand cpufreq_stats freq_table cpufreq_conservative cpufreq_userspace video output ac battery sbs sbshc dock container microcode msr iptable_filter ip_tables x_tables xfs nfs lockd nfs_acl sunrpc parport_pc lp parport loop iTCO_wdt iTCO_vendor_support serio_raw i5000_edac edac_core psmouse button pcspkr shpchp evdev pci_hotplug ext3 jbd mbcache sg sd_mod ahci ehci_hcd libata uhci_hcd scsi_mod e1000 usbcore raid10 raid456 async_xor async_memcpy async_tx xor raid1 raid0 multipath linear md_mod thermal processor fan fbcon tileblit font bitblit softcursor fuse
Pid: 26534, comm: atftpd Not tainted 2.6.24-23-server #1
RIP: 0010:[<ffffffff882968b2>]  [<ffffffff882968b2>] :sunrpc:rpcb_getport_async+0x272/0x3c0
RSP: 0018:ffff8100058837c8  EFLAGS: 00010206
RAX: ffffffff882b45c0 RBX: ffff810154c4fe00 RCX: ffffffff80288483
RDX: ffffffff882b45c0 RSI: 0000000000011200 RDI: ffff810151574300
RBP: ffff810155090000 R08: 0000000000000000 R09: 000000000000006b
R10: 0000000000000001 R11: ffffffff88296640 R12: ffff810159d13600
R13: ffff810151574300 R14: ffff810005883898 R15: ffff8100058839c8
FS:  000000004310e950(0063) GS:ffff81015ac01800(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 00007fc95fb60000 CR3: 0000000151554000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process atftpd (pid: 26534, threadinfo ffff810005882000, task ffff810158806000)
Stack:  ffff810151574300 ffffffff8831e198 ffff8101574c4a80 ffffffff882878c0
 0000000000000000 ffff810151574300 ffffffff8829c390 ffff8101515743f0
 ffff810005883898 ffffffff8828db3b ffffffff8829c390 ffff810151574300
Call Trace:
 [<ffffffff882878c0>] :sunrpc:call_allocate+0xc0/0x1b0
 [<ffffffff8828db3b>] :sunrpc:__rpc_execute+0x6b/0x290
 [<ffffffff88286f86>] :sunrpc:rpc_do_run_task+0x76/0xd0
 [<ffffffff88287045>] :sunrpc:rpc_call_sync+0x15/0x40
 [<ffffffff882f1fff>] :nfs:nfs4_proc_access+0x8f/0x1e0
 [<ffffffff802934ad>] zone_statistics+0x7d/0x80
 [<ffffffff8028bdfb>] get_page_from_freelist+0x47b/0x6c0
 [<ffffffff882db84a>] :nfs:nfs_do_access+0xda/0x350
 [<ffffffff882dbb98>] :nfs:nfs_permission+0xd8/0x1a0
 [<ffffffff802bd430>] permission+0xb0/0x160
 [<ffffffff802bf767>] __link_path_walk+0x87/0xe90
 [<ffffffff802c05cb>] link_path_walk+0x5b/0x100
 [<ffffffff802b3337>] get_unused_fd_flags+0x77/0x120
 [<ffffffff802cbcb8>] touch_atime+0x88/0x160
 [<ffffffff802bfd4a>] __link_path_walk+0x66a/0xe90
 [<ffffffff802c05cb>] link_path_walk+0x5b/0x100
 [<ffffffff802b3337>] get_unused_fd_flags+0x77/0x120
 [<ffffffff802c088a>] do_path_lookup+0x8a/0x250
 [<ffffffff802c174a>] __path_lookup_intent_open+0x6a/0xd0
 [<ffffffff802c1979>] open_namei+0x89/0x710
 [<ffffffff803e3d00>] sys_sendto+0x1a0/0x1b0
 [<ffffffff802b36dc>] do_filp_open+0x1c/0x50
 [<ffffffff802b3337>] get_unused_fd_flags+0x77/0x120
 [<ffffffff802b376a>] do_sys_open+0x5a/0xf0
 [<ffffffff8020c39e>] system_call+0x7e/0x83


Code: 0f 0b eb fe 8b 85 b8 00 00 00 0f b7 b7 48 01 00 00 48 c7 c2 
RIP  [<ffffffff882968b2>] :sunrpc:rpcb_getport_async+0x272/0x3c0
RSP <ffff8100058837c8>
---[ end trace 87bd2526910262f1 ]---