On Fri, Jun 13, 2008 at 09:53:03AM -0700, David Daney wrote:

From: David Daney <redacted>
Date: Fri, 13 Jun 2008 09:53:03 -0700
To: Thomas Horsten <redacted>
Cc: linux-mips@linux-mips.org, Ralf Baechle <redacted>
Subject: Re: [BUG] R5000 failure in kmap_coherent on Lasat board, bug that
	has been there for a while?
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Thomas Horsten wrote:

quoted

Hi all,

(resending w/ more info because the first one didn't make it to the
list - I'm subscribed now so hopefully it'll go through this time):

This crash happens (late) during boot with 2.6.25.6. I think this is a
general R5k issue with the cache handling code. It only seems to
happen when the swap is in use like someone else observed, but usually
only after some big processes like mysql have been started.

As far as I can see it's the same issue that has been reported several
other places, but with no resolution in any of them:

http://www.linux-mips.org/archives/linux-mips/2007-12/msg00128.html
http://www.linux-mips.org/archives/linux-mips/2008-01/msg00132.html
and also seen by someone else here:
http://lists.debian.org/debian-mips/2007/11/msg00034.html

I'm thinking some subtle difference between R4k and R5k caches which
isn't taken into account, or an aliasing bug that only triggers on
R5k?

I have a mips 4KEc based system where I think it is happening too (sigma8634 based w/ 2.6.15 kernel).

quoted

I also found what seems to be a related patch from OpenWRT but I have
no idea what it's supposed to solve as I could only find the raw
patch:

https://dev.openwrt.org/browser/trunk/target/linux/brcm47xx/patches-2.6.25/160-kmap_coherent.patch?rev=11155

In any case I tried to apply it to my Lasat kernel, but using the
_atomic functions instead of _coherent just causes a much earlier
crash.

I will try said patch on my O2/R5000 and the sigma8634.

The patch is total bullshit.  It doesn't even try to fix the issues but
rather disables the alias-avoidance mechanism.

  Ralf