Bug#538000: I've seen this, too.
We saw the same thing here after restarting the nfs-kernel-server. Only
happened once over multiple attempts.
Also, google found this:
http://linux-nfs.org/pipermail/nfsv4/2009-March/009994.html
roland:~# uname -a
Linux roland 2.6.26-2-amd64 #1 SMP Thu Nov 5 02:23:12 UTC 2009 x86_64
GNU/Linux
Dec 7 16:40:17 roland mountd[4796]: Caught signal 15, un-registering
and exiting.
Dec 7 16:40:17 roland kernel: [12530.470314] nfsd: last server has exited
Dec 7 16:40:17 roland kernel: [12530.470314] nfsd: unexporting all
filesystems
Dec 7 16:40:33 roland kernel: [12551.414833] NFSD: Using
/var/lib/nfs/v4recovery as the NFSv4 state recovery directory
Dec 7 16:40:33 roland kernel: [12551.414846] NFSD: starting 90-second
grace period
Dec 7 16:40:34 roland kernel: [12551.842442] ------------[ cut here
]------------
Dec 7 16:40:34 roland kernel: [12551.842442] kernel BUG at
include/linux/module.h:386!
Dec 7 16:40:34 roland kernel: [12551.842442] invalid opcode: 0000 [1] SMP
Dec 7 16:40:34 roland kernel: [12551.842442] CPU 0
Dec 7 16:40:34 roland kernel: [12551.842442] Modules linked in: nfsd
lockd nfs_acl auth_rpcgss sunrpc exportfs ipv6 xfs loop ipmi_si snd_pcm
snd_timer snd soundcore snd_page_alloc usbhid psmouse hpilo hid
ipmi_msghandler pcspkr serio_raw ff_memless container button evdev ext3
jbd mbcache ehci_hcd uhci_hcd bnx2 firmware_class e1000e cciss scsi_mod
thermal processor fan thermal_sys [last unloaded: scsi_wait_scan]
Dec 7 16:40:34 roland kernel: [12551.842442] Pid: 4874, comm: nfsd Not
tainted 2.6.26-2-amd64 #1
Dec 7 16:40:34 roland kernel: [12551.842442] RIP:
0010:[<ffffffffa0240e67>] [<ffffffffa0240e67>] :sunrpc:svc_recv+0x41d/0x70e
Dec 7 16:40:34 roland kernel: [12551.842442] RSP:
0018:ffff81061b45fe90 EFLAGS: 00010246
Dec 7 16:40:34 roland kernel: [12551.842442] RAX: 0000000000000000 RBX:
ffffffffa0258d80 RCX: 0000000000000000
Dec 7 16:40:34 roland kernel: [12551.842442] RDX: 0000000000001000 RSI:
ffff81061b45fdb0 RDI: ffffffffa0258d80
Dec 7 16:40:34 roland kernel: [12551.842442] RBP: ffff810615902000 R08:
ffff8103179757c0 R09: 0000000000000000
Dec 7 16:40:34 roland kernel: [12551.842442] R10: ffff81000103b8f0 R11:
ffffffff803feabc R12: ffff81061c871000
Dec 7 16:40:34 roland kernel: [12551.842442] R13: ffff81031e4ab800 R14:
ffff81061bd9b7c0 R15: ffff81061d283680
Dec 7 16:40:34 roland kernel: [12551.842442] FS:
00007fc68d0236e0(0000) GS:ffffffff8053c000(0000) knlGS:0000000000000000
Dec 7 16:40:34 roland kernel: [12551.842442] CS: 0010 DS: 0000 ES:
0000 CR0: 000000008005003b
Dec 7 16:40:34 roland kernel: [12551.842442] CR2: 00007fb17e1fd000 CR3:
000000031b9b5000 CR4: 00000000000006e0
Dec 7 16:40:34 roland kernel: [12551.842442] DR0: 0000000000000000 DR1:
0000000000000000 DR2: 0000000000000000
Dec 7 16:40:34 roland kernel: [12551.842442] DR3: 0000000000000000 DR6:
00000000ffff0ff0 DR7: 0000000000000400
Dec 7 16:40:34 roland kernel: [12551.842442] Process nfsd (pid: 4874,
threadinfo ffff81061b45e000, task ffff81061b45d930)
Dec 7 16:40:34 roland kernel: [12551.842442] Stack: ffff81031c8d4018
00000000000dbba0 0000000000000000 ffff81061b45d930
Dec 7 16:40:34 roland kernel: [12551.842442] ffffffff8022c244
0000000000100100 0000000000200200 ffffffff8042a274
Dec 7 16:40:34 roland kernel: [12551.842442] 01000000804f9b20
0000000000000001 ffff810615902000 ffffffffa028267c
Dec 7 16:40:34 roland kernel: [12551.842442] Call Trace:
Dec 7 16:40:34 roland kernel: [12551.842442] [<ffffffff8022c244>] ?
default_wake_function+0x0/0xe
Dec 7 16:40:34 roland kernel: [12551.842442] [<ffffffff8042a274>] ?
__down_read+0x12/0xa1
Dec 7 16:40:34 roland kernel: [12551.842442] [<ffffffffa028267c>] ?
:nfsd:nfsd+0x0/0x2a4
Dec 7 16:40:34 roland kernel: [12551.842442] [<ffffffffa0282767>] ?
:nfsd:nfsd+0xeb/0x2a4
Dec 7 16:40:34 roland kernel: [12551.842442] [<ffffffff802301c9>] ?
schedule_tail+0x27/0x5c
Dec 7 16:40:34 roland kernel: [12551.842442] [<ffffffff8020cf28>] ?
child_rip+0xa/0x12
Dec 7 16:40:34 roland kernel: [12551.842442] [<ffffffffa028267c>] ?
:nfsd:nfsd+0x0/0x2a4
Dec 7 16:40:34 roland kernel: [12551.842442] [<ffffffffa028267c>] ?
:nfsd:nfsd+0x0/0x2a4
Dec 7 16:40:34 roland kernel: [12551.842442] [<ffffffffa028267c>] ?
:nfsd:nfsd+0x0/0x2a4
Dec 7 16:40:34 roland kernel: [12551.842442] [<ffffffff8020cf1e>] ?
child_rip+0x0/0x12
Dec 7 16:40:34 roland kernel: [12551.842442]
Dec 7 16:40:34 roland kernel: [12551.842442]
Dec 7 16:40:34 roland kernel: [12551.842442] Code: 08 4c 89 e7 ff 50 08
48 85 c0 49 89 c5 0f 84 48 01 00 00 48 8b 00 48 8b 58 08 48 85 db 74 26
48 89 df e8 c4 14 01 e0 85 c0 75 04 <0f> 0b eb fe 65 8b 04 25 24 00 00
00 89 c0 48 c1 e0 07 48 ff 84
Dec 7 16:40:34 roland kernel: [12551.842442] RIP [<ffffffffa0240e67>]
:sunrpc:svc_recv+0x41d/0x70e
Dec 7 16:40:34 roland kernel: [12551.842442] RSP <ffff81061b45fe90>
Dec 7 16:40:34 roland kernel: [12551.842442] ---[ end trace
90deb7ede2c3cf43 ]---
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