Re: [BUG] R5000 failure in kmap_coherent on Lasat board, bug that has been there for a while?

[Ralf Baechle <ralf@linux-mips.org>]

On Fri, Jun 13, 2008 at 09:53:03AM -0700, David Daney wrote:
> From: David Daney <ddaney@avtrex.com>
> Date: Fri, 13 Jun 2008 09:53:03 -0700
> To: Thomas Horsten <thomas@horsten.com>
> Cc: linux-mips@linux-mips.org, Ralf Baechle <ralf@linux-mips.org>
> 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:
>> 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).
>
>
>>
>> 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