BUG: unable to handle kernel NULL pointer dereference at 00000048

[Slicky Devil <slicky.dvl-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Hello!

I think I found a bug for you, guys.

The situation was as following. At first, I set up LVM with a single
lv (with nilfs) for root. Everything worked fine. Then I decided to
create a separate home partition. I shrank the root a bit, created
another nilfs logical volume for home. Then I shrank root/expanded
home a couple of times. In the end I got the bug, when tried to mount
the home.

I'm pretty much confident (say 90%) that I didn't mess things up by
shrinking a partition before resizing the appropriate filesystem.

Now every time I try to mount home I get the following:

[ 1367.830334] BUG: unable to handle kernel NULL pointer dereference at 00000048
[ 1367.831581] IP: [<d0d7a08e>] nilfs_load_super_block+0x17e/0x280 [nilfs2]
[ 1367.832098] *pde = 00000000
[ 1367.832596] Oops: 0000 [#1] PREEMPT SMP
[ 1367.833098] Modules linked in: ext2 mbcache snd_intel8x0 e1000
ppdev snd_ac97_codec ac97_bus snd_pcm snd_page_alloc vboxvideo(O)
snd_timer drm snd agpgart parport_pc soundcore parport i2c_piix4
i2c_core serio_raw psmouse pcspkr evdev joydev processor ac button
vboxsf(O) vboxguest(O) nilfs2 dm_mod sr_mod cdrom sd_mod usbhid hid
ahci libahci libata ohci_hcd scsi_mod usbcore usb_common
[ 1367.833562]
[ 1367.833562] Pid: 710, comm: mount.nilfs2 Tainted: G           O
3.2.6-2-ARCH #1 innotek GmbH VirtualBox
[ 1367.833562] EIP: 0060:[<d0d7a08e>] EFLAGS: 00010202 CPU: 0
[ 1367.833562] EIP is at nilfs_load_super_block+0x17e/0x280 [nilfs2]
[ 1367.833562] EAX: c9cb6400 EBX: ce845e00 ECX: 00000000 EDX: 00000000
[ 1367.833562] ESI: 00000001 EDI: 00000000 EBP: ca9bbe08 ESP: ca9bbdcc
[ 1367.833562]  DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
[ 1367.833562] Process mount.nilfs2 (pid: 710, ti=ca9ba000
task=cf054d20 task.ti=ca9ba000)
[ 1367.833562] Stack:
[ 1367.833562]  00000400 ce845e1c 0013f800 00000000 00000000 00000000
cc7d6c00 00000400
[ 1367.833562]  00000001 00000001 00000001 00000001 ce845e00 ca9bbe30
cc7d6c00 ca9bbe40
[ 1367.833562]  d0d7a87b ca9bbe30 00000114 000080d0 00000200 00034460
cc7d6db0 00000000
[ 1367.833562] Call Trace:
[ 1367.833562]  [<d0d7a87b>] init_nilfs+0x4b/0x2e0 [nilfs2]
[ 1367.833562]  [<d0d6f707>] nilfs_mount+0x447/0x5b0 [nilfs2]
[ 1367.833562]  [<c01f33a4>] ? pcpu_alloc+0x714/0x810
[ 1367.833562]  [<c02d2add>] ? ida_get_new_above+0x1ad/0x230
[ 1367.833562]  [<c02d2add>] ? ida_get_new_above+0x1ad/0x230
[ 1367.833562]  [<c0226636>] mount_fs+0x36/0x180
[ 1367.833562]  [<c01f34af>] ? __alloc_percpu+0xf/0x20
[ 1367.833562]  [<c023d961>] vfs_kern_mount+0x51/0xa0
[ 1367.833562]  [<c023ddae>] do_kern_mount+0x3e/0xe0
[ 1367.833562]  [<c023f189>] do_mount+0x169/0x700
[ 1367.833562]  [<c01eeb29>] ? strndup_user+0x49/0x70
[ 1367.833562]  [<c023fa9b>] sys_mount+0x6b/0xa0
[ 1367.833562]  [<c04abd1f>] sysenter_do_call+0x12/0x28
[ 1367.833562] Code: 53 18 8b 43 20 89 4b 18 8b 4b 24 89 53 1c 89 43
24 89 4b 20 8b 43 20 c7 43 2c 00 00 00 00 23 75 e8 8b 50 68 89 53 28
8b 54 b3 20 <8b> 72 48 8b 7a 4c 8b 55 08 89 b3 84 00 00 00 89 bb 88 00
00 00
[ 1367.833562] EIP: [<d0d7a08e>] nilfs_load_super_block+0x17e/0x280
[nilfs2] SS:ESP 0068:ca9bbdcc
[ 1367.833562] CR2: 0000000000000048
[ 1367.855410] ---[ end trace 0b5fed15fa08cff2 ]---

The kernel is the standard archlinux "stocK" kernel run within
virtualbox: Linux arch1 3.2.6-2-ARCH #1 SMP PREEMPT Thu Feb 16
10:23:00 UTC 2012 i686 Intel(R) Core(TM) i5 CPU 650 @ 3.20GHz
GenuineIntel GNU/Linux

I can provide the partition superblock, if necessary.

Cheers!
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