Comment 9 for bug 150788

Same here. Kernel is 2.6.22-14-generic_2.6.22-14.35_i386.

The patch from bug #85145 does NOT solve this problem (took the patch from ubuntu-feisty git tree: a47c7c9186612ad5f59bcca95bd5fac5cb01b287).

We are using ubuntu for our netboot thin clients. Root fs is nfs ro mounted, /etc and /var are mounted as union to a tmpfs in an init script. We have been using this technique since ubuntu dapper and it always has worked.

Here is the oops:

[ 9.664000] BUG: unable to handle kernel NULL pointer dereference at virtual address 00000004
[ 9.664000] printing eip:
[ 9.664000] e01f6c42
[ 9.664000] *pde = 00000000
[ 9.664000] Oops: 0000 [#1]
[ 9.664000] SMP
[ 9.664000] Modules linked in: unionfs netconsole af_packet nfs lockd sunrpc b44 mii ehci_hcd uhci_hcd usbcore raid10 raid456 xor raid1 raid0 multipath linear md_mod dm_mirror dm_snapshot dm_mod thermal processor fan fuse apparmor commoncap
[ 9.668000] CPU: 0
[ 9.668000] EIP: 0060:[<e01f6c42>] Not tainted VLI
[ 9.668000] EFLAGS: 00010246 (2.6.22-14-generic #1)
[ 9.668000] EIP is at nfs_lookup+0xd2/0x260 [nfs]
[ 9.668000] eax: 00000000 ebx: e021aec0 ecx: 00000000 edx: ddc5cb08
[ 9.668000] esi: 00000000 edi: de15f000 ebp: 00000000 esp: deb9bbc4
[ 9.668000] ds: 007b es: 007b fs: 00d8 gs: 0033 ss: 0068
[ 9.668000] Process bash (pid: 2514, ti=deb9a000 task=de3a59f0 task.ti=deb9a000)
[ 9.668000] Stack: deb9bbd8 00000000 00000000 ddc5cb08 0007c89a 00000006 470e2508 00000000
[ 9.668000] 470ccf4c 00000000 470ccf4d 00000000 00000005 0000a1ff 00000001 00000000
[ 9.668000] 00000000 00000025 00000000 00000000 00000000 00000000 00009302 00000000
[ 9.668000] Call Trace:
[ 9.668000] [<e01f656e>] nfs_lookup_revalidate+0x24e/0x450 [nfs]
[ 9.668000] [<e01f75ec>] nfs_access_get_cached+0x1c/0x110 [nfs]
[ 9.668000] [<e01f77c1>] nfs_permission+0xe1/0x1f0 [nfs]
[ 9.668000] [<e016438b>] unionfs_read_inode+0x7b/0xd0 [unionfs]
[ 9.668000] [<c01926d9>] d_alloc+0x109/0x190
[ 9.668000] [<c01896a6>] lookup_one_len_nd+0xe6/0x110
[ 9.672000] [<e016936a>] unionfs_lookup_backend+0x36a/0x880 [unionfs]
[ 9.672000] [<c01925eb>] d_alloc+0x1b/0x190
[ 9.672000] [<c01926d9>] d_alloc+0x109/0x190
[ 9.672000] [<c0187ef8>] do_lookup+0x148/0x190
[ 9.672000] [<c018a017>] __link_path_walk+0x867/0xe70
[ 9.672000] [<c02183b7>] vgacon_scroll+0x107/0x1d0
[ 9.672000] [<c024f3b1>] scrup+0xe1/0xf0
[ 9.672000] [<c018a665>] link_path_walk+0x45/0xc0
[ 9.672000] [<c018a8d7>] do_path_lookup+0x97/0x1d0
[ 9.672000] [<c018b541>] __path_lookup_intent_open+0x51/0xa0
[ 9.672000] [<c018b620>] path_lookup_open+0x20/0x30
[ 9.672000] [<c018b71a>] open_namei+0x5a/0x600
[ 9.672000] [<c016ce18>] __handle_mm_fault+0x288/0xb00
[ 9.672000] [<c017edf3>] do_filp_open+0x33/0x60
[ 9.672000] [<c017ee6e>] do_sys_open+0x4e/0xf0
[ 9.672000] [<c017ef4c>] sys_open+0x1c/0x20
[ 9.672000] [<c01041d2>] sysenter_past_esp+0x6b/0xa9
[ 9.672000] =======================
[ 9.672000] Code: 24 0c 8d 57 1c 89 0c 24 8d 8c 24 a6 00 00 00 ff 53 20 31 d2 83 f8 fe 74 6f 85 c0 89 c6 0f 88 0a 01 00 00 8b 54 24 0c 8b 4c 24 5c <8b> 6d 04 8b 82 98 00 00 00 8b 98 64 01 00 00 8b 53 7c 8d 73 78
[ 9.676000] EIP: [<e01f6c42>] nfs_lookup+0xd2/0x260 [nfs] SS:ESP 0068:deb9bbc4