2.6.8-rc4 + nfsd: Unable to handle kernel NULL pointer dereference

Hello,

I tried 2.6.8-rc4 and found following, 2.6.6 and 2.6.7 are fine:

<1>Unable to handle kernel NULL pointer dereference at 0000000000000003 RIP: <ffffffff801e6cce>{nfssvc_decode_readargs+238} PML4 77661067 PGD 7778f067 PMD 78ad8067 PTE 0

Oops: 0000 [4] SMP
CPU 0
Pid: 3436, comm: nfsd Not tainted 2.6.8-rc4
RIP: 0010:[<ffffffff801e6cce>]
<ffffffff801e6cce>{nfssvc_decode_readargs+238}
RSP: 0018:000001007dd9fe68  EFLAGS: 00010206
RAX: 0000000000000000 RBX: 000001007fc19400 RCX: 000001007fc18c90
RDX: 00000000ffff8488 RSI: 000001007fc4b6ac RDI: 00000000ffff7488
RBP: 000001007fc18c00 R08: 000000000000000a R09: 0000000000000009
R10: 0000010000000000 R11: 6db6db6db6db6db7 R12: 000001007fc4b680
R13: 000001007dd2b014 R14: ffffffff803bb5a0 R15: 000001007fc19468
FS:  0000002a980ab060(0000) GS:ffffffff804ae6c0(0000)

knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 0000000000000003 CR3: 0000000000101000 CR4: 00000000000006e0 Process nfsd (pid: 3436, threadinfo 000001007dd9e000, task 000001007782c0f0)

Stack: 000001007fc19400 ffffffff803bb2f0 ffffffff803bb2f0
ffffffff801ddd00
       000001007fc19468 000001007fc19400 000001007fc194a0
ffffffff803bb2f0
       000001007dd2b014 ffffffff80345a99
Call Trace:<ffffffff801ddd00>{nfsd_dispatch+128}
<ffffffff80345a99>{svc_process+937}
       <ffffffff801dd8b0>{nfsd+0} <ffffffff801ddae4>{nfsd+564}
       <ffffffff8012d811>{schedule_tail+17}
<ffffffff8010f887>{child_rip+8}
       <ffffffff801dd8b0>{nfsd+0} <ffffffff801dd8b0>{nfsd+0}
       <ffffffff8010f87f>{child_rip+0}

Code: 48 0f b6 50 03 48 8b 14 d5 00 28 48 80 48 2b 82 c8 03 00 00

RIP <ffffffff801e6cce>{nfssvc_decode_readargs+238} RSP <000001007dd9fe68>
CR2: 0000000000000003

This is two way amd64 server which is serving couple of thin clients over nfs.

Linux HAL9000 2.6.6 #1 SMP Sat May 15 08:11:53 MDT 2004 x86_64 5 GNU/Linux

Gnu C                  3.3.3
Gnu make               3.80
binutils               2.15.90.0.1.1
util-linux             2.12
mount                  2.12
module-init-tools      3.0
e2fsprogs              1.35
nfs-utils              1.0.6
Linux C Library        2.3.2
Dynamic linker (ldd)   2.3.2
Procps                 3.2.1
Net-tools              1.60
Kbd                    1.12
Sh-utils               5.2.1

BR, Jani

I narrowed this down to the 2.6.8rc4, 2.6.8rc3 works ok. And this happens (on server) every time, when thin client tried mount root-fs from server.