[Unionfs] kernel BUG at fs/unionfs/super.c:106!

[Simon Sasburg]

I got an external usb hard disk which I was going to add to my union.

After formatting the disk, mounting it, i unmounted my union, edited
/etc/fstab to add a branch on the new disk to it, and mounted it
again.

After a while, i noticed the union seemed empty, doing 'ls' in the
mountpoint i got some error about stale inodes.

I thought, oh well, i'll remount the union, but unmount produced a
segmentation fault and the following appeared in dmesg output:
[42156.142236] unionfs: branch 0 has 6 references left!
[42156.142244] unionfs: branch 1 has 6 references left!
[42156.142247] unionfs: branch 2 has 6 references left!
[42156.142249] unionfs: branch 3 has 6 references left!
[42156.142250] unionfs: branch 4 has 6 references left!
[42156.142317] ------------[ cut here ]------------
[42156.142321] kernel BUG at fs/unionfs/super.c:106!
[42156.142324] invalid opcode: 0000 [#1]
[42156.142326] Modules linked in: nls_utf8 ntfs via drm vmnet(P)
vmmon(P) binfmt_misc capability commoncap container unionfs ext2
nls_iso8859_1 nls_cp437 ipv6 fuse usb_storage snd_via82xx gameport
snd_ac97_codec ac97_bus snd_pcm_oss snd_mixer_oss snd_pcm
snd_page_alloc snd_mpu401_uart snd_seq_dummy snd_seq_oss snd_seq_midi
snd_rawmidi snd_seq_midi_event snd_seq snd_timer snd_seq_device
libusual pcspkr serio_raw 8250_pnp 8250 serial_core parport_pc parport
af_packet i2c_viapro snd soundcore i2c_core via_agp agpgart evdev
floppy ehci_hcd ide_disk uhci_hcd usbcore thermal processor fan
[42156.142363] CPU:    0
[42156.142364] EIP:    0060:[<f8a89026>]    Tainted: P       VLI
[42156.142365] EFLAGS: 00010202   (2.6.22.6-u2.1-b1 #1)
[42156.142383] EIP is at unionfs_put_super+0x86/0x90 [unionfs]
[42156.142386] eax: 0000003b   ebx: 00000005   ecx: 00000001   edx: 00017baa
[42156.142389] esi: eb07e800   edi: 00000005   ebp: f29b1c80   esp: e927ff18
[42156.142392] ds: 007b   es: 007b   fs: 0000  gs: 0033  ss: 0068
[42156.142396] Process umount (pid: 26616, ti=e927e000 task=dfc74550
task.ti=e927e000)
[42156.142398] Stack: f8a93138 00000004 00000006 eb07e800 f8a976a0
eb07e848 e927e000 c01756da
[42156.142404]        00000246 eb07e800 eb07e800 f8a97680 08062a28
c0175b2d 00000000 08062a09
[42156.142410]        c018f6a9 f717eed4 d18117c0 b7e4f36f 00000004
c039a522 00000001 00000001
[42156.142415] Call Trace:
[42156.142421]  [<c01756da>] generic_shutdown_super+0x6a/0x100
[42156.142434]  [<c0175b2d>] deactivate_super+0x4d/0x90
[42156.142440]  [<c018f6a9>] sys_oldumount+0x39/0x80
[42156.142448]  [<c039a522>] do_page_fault+0x342/0x620
[42156.142462]  [<c01041c6>] sysenter_past_esp+0x5f/0x89
[42156.142473]  =======================
[42156.142475] Code: 01 00 00 00 75 ca 85 c9 75 21 8b 45 18 e8 63 65
6e c7 89 e8 e8 5c 65 6e c7 c7 86 4c 01 00 00 00 00 00 00 83 c4 0c 5b
5e 5f 5d c3 <0f> 0b eb fe 8d b6 00 00 00 00 55 57 56 89 d6 53 89 c3 83
ec 04
[42156.142496] EIP: [<f8a89026>] unionfs_put_super+0x86/0x90 [unionfs]
SS:ESP 0068:e927ff18
[42156.142508] WARNING: at kernel/exit.c:869 do_exit()
[42156.142511]  [<c011c835>] do_exit+0x745/0x7b0
[42156.142517]  [<c02a9e13>] do_unblank_screen+0x23/0x1c0
[42156.142525]  [<c0104fc7>] die+0x1e7/0x1f0
[42156.142531]  [<c01052f0>] do_invalid_op+0x0/0x90
[42156.142535]  [<c0105371>] do_invalid_op+0x81/0x90
[42156.142541]  [<f8a89026>] unionfs_put_super+0x86/0x90 [unionfs]
[42156.142558]  [<c039844a>] error_code+0x6a/0x70
[42156.142565]  [<f8a89026>] unionfs_put_super+0x86/0x90 [unionfs]
[42156.142575]  [<c01756da>] generic_shutdown_super+0x6a/0x100
[42156.142581]  [<c0175b2d>] deactivate_super+0x4d/0x90
[42156.142586]  [<c018f6a9>] sys_oldumount+0x39/0x80
[42156.142591]  [<c039a522>] do_page_fault+0x342/0x620
[42156.142600]  [<c01041c6>] sysenter_past_esp+0x5f/0x89
[42156.142609]  =======================

I'm using kernel 2.6.22.6 with the unionfs 2.1.2 patch for 2.6.22.4,
as there is no patch for .6 yet. Could this be the problem or is it
something else?

-
Simon