MCE on an NForce4 board (again)

[Jack Malmostoso]

Hi there list,

this is a repost from the x86-64.org discuss list. I think it could be
relevant here too, if not please excuse me and forget this message. I am not
subscribed to the LKML, but I can follow the thread on usenet, so no need to
CC. Feel free to do it if you think it's relevant!

Since a couple of days I have been experiencing weird lockups on my AMD64
machine running Debian Sid.
The computer is composed like this:

Asus A8N-E (NForce4 socket 939)
Athlon64 X2 3800+
2x512MB Corsair TwinX
2x250GB Sata Western Digital
2xDVD/DVDRW on PATA channels

None of the components has *ever* been overclocked and the whole is one year
old.

I have logged on in single mode and tried to find a way to reproduce the
crash. It has been enough to do a stupid script like

while true; do
tar -xjvf linux-2.6.20.3.tar.bz2 && rm -fr linux-2.6.20.3
done

and regularly, after one or two cycles, the system would lockup with this
error:

CPU 0: Machine Check Exception:		4 Bank 4: b200000000070f0f
TSC 185ef6d81ca

It also gave me the hint to use mcelog, so I rebooted and installed it. The
decoded error read:

CPU 0 4 northbridge TSC 185ef6d81ca 
  Northbridge Watchdog error
       bit57 = processor context corrupt
       bit61 = error uncorrected
  bus error 'generic participation, request timed out
      generic error mem transaction
      generic access, level generic'
STATUS b200000000070f0f MCGSTATUS 4

I googled and found a thread on the x86-64.org discuss list [1] that blamed
the RAM for the
problem. So I have started doing some tests:

1) If I use only 512MB of my RAM, alternatively, I don't get the error.
2) Memtest+ has been running for 10hrs and no errors have been detected.
I'll have it running for the day just to be sure.

Additionally, right before the MCE, I could read another error:

ata3: CPB flags CMD err, flags=0x11

Googling this brought up some threads in the LKML about the sata_nv driver
(the ADMA bit, I think).

Since I am running a 2.6.20 kernel (a testing version from the Debian kernel
team) I have tried booting older kernels but looks like anything I have
tried does not work (but this is not your problem).

So I have booted a livecd (I had around an Ubuntu with a 2.6.12 kernel) and
with my great surprise the machine worked without problems.

Now, do you think it would be even slightly possible that some regression in
the sata_nv module could trigger an MCE? If not, would you put your money on
the RAM, or could the motherboard be blamed? I hope it's not the CPU ;)

Thanks for your help, I hope the information I gave you is enough. Please
feel free to suggest any more tests and diagnostics!

[1] https://www.x86-64.org/pipermail/discuss/2005-March/005902.html 
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