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SubjectRe: BUG: unable to handle kernel NULL pointer dereference - nfs v3
On Monday July 16, wrote:
> Hi,
> I'm not sure is the good place to poste that, and if not - please excuse me.

This is the correct place to post this, thanks.

> I was running nfs server v2 since a year on one server, there is few days, i
> have update my kernel to with support of nfsv3 server.
> Somes times per days i have somes crash as below, needing i reboot the server
> to nfs re-become up.
> ************
> BUG: unable to handle kernel NULL pointer dereference at virtual address
> 00000004

This says that it tried to access memory at address '4'. There is no
memory there, so it caused the BUG.

> printing eip:
> c01e7279
> *pde = 09ecc001
> Oops: 0000 [#1]
> CPU: 0
> EIP: 0060:[<c01e7279>] Not tainted VLI
> EFLAGS: 00010246 ( #9)

What is "-sdf88-core" ?? Are there any extra patches that we should
know about?

> EIP is at encode_fsid+0x67/0x89

This is presumably where the illegal access happened.

> eax: e5bde8c0 ebx: f7593404 ecx: 00000000 edx: 00000006
> esi: dc569048 edi: f75934ec ebp: f7593404 esp: f75f1f18

Memory accesses are (almost) always relative to the value in some
register. Of these registers, the most likely is ecx, with edx a
vague possibility.

> Code: e2 08 09 d1 09 c1 eb 10 8b 83 88 00 00 00 8b 40 30 89 c3 89 c1 c1 fb 1f
> 89 d8 0f c8 89 06 89 c8 eb 1e

Unfortunately "ksymoops" does seem to decode this into something quite
useful enough. Normally one of the numbers has <> around it. Are you
should you copied the number across exactly?

This code decodes as:
0: e2 08 loop a <_EIP+0xa>
2: 09 d1 or %edx,%ecx
4: 09 c1 or %eax,%ecx
6: eb 10 jmp 18 <_EIP+0x18>
8: 8b 83 88 00 00 00 mov 0x88(%ebx),%eax
e: 8b 40 30 mov 0x30(%eax),%eax
11: 89 c3 mov %eax,%ebx

From the 'jmp' onwards, that is what I would expect to see in
encode_fsid. The code before there doesn't make a lot of sense, so
it is hard to pinpoint exactly there the error is.

In any case, there is no place in encode_fsid where an offset of 4
from any register is indexed, nor an offset of -2.
So either there is something wrong with the decoding and displaying
of this information, or there is something very wrong with your

I would suggest:
1/ if possible, run memtest86 on the machine for a while, to make
sure there isn't a problem with the memory.
2/ If the problem happens again, post another report with all the
"oops" information again. Maybe the next time it will be slightly
different and will make more sense in some way.


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