Re: Sparc32 not working:2.6.23-rc1 (git commit 1e4dcd22efa7d24f637ab2ea3a77dd65774eb005)

Re: Sparc32 not working:2.6.23-rc1 (git commit 1e4dcd22efa7d24f637ab2ea3a77dd65774eb005)

[Mark Fortescue]

Hi David,

I have finally located where my NULL pointer is. The problem is that I 
have not got a clue how it is getting set to NULL.

In arch/sparc/mm/sun4c.c, add_ring_ordered, head->next is getting 
corrupted and is becoming a NULL pointer. This is ment to be a circular 
linked list so it should never be NULL.

The simple explenation, since nothing significant apears to have changed 
in sun4c.c, is that some change in mm/memory.c is wrong/incompatible with 
sun4c mmu. The problem is that all the kernels I tried to build around the 
changes to the mm code don't build on Sparc32 due to the DMA changes. This 
makes it more dificult to be cirtain of the cause of the corruption.

I am going to try to back out the mm/memory.c changes so that I can 
eliminate them as a cause.

Unless someone who understands the memory management code spots an error, 
this is not going to be easy to track down and fix.

Do you have any documentation on the sun4c mmu?

If not, I am going to have to create some diagrams/documentation as 
tralling through the code takes forever and gets very confusing. I am 
struggel to understand what tables have what in them for the sun4c mmu.

Regards
 	Mark Fortescue.

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Re: Sparc32 not working:2.6.23-rc1 (git commit 1e4dcd22efa7d24f637ab2ea3a77dd65774eb005)

[Mark Fortescue]

On Sun, 29 Jul 2007, Krzysztof Helt wrote:

> On Sun, 29 Jul 2007 00:21:06 +0100 (BST)
> Mark Fortescue <mark@mtfhpc.demon.co.uk> wrote:
>
>> Hi Krzysztof,
>>
>> There have been lots of changes to the DMA system (git bisect is not
>> viable form my working 2.6.22 kernel as the dma changes kill the build for
>> over half the posible commits to check). It could be a side effect of
>> these changes.
>>
>
> It is not DMA I suppose. It does not happen in any specific place. It is easy to trigger by loading
> and unloading the sunlance module, but it hangs linux in other places (init process, console login).
>
> It happens only in SMP. If it happens in the sunlance module it happens in sparc_lance_probe_one()
> (in probing function). I thought it is due to openprom accesses so I commented them out (and put
> hardcoded values there). No real change. It is always in the probe_one method before any DMA is
> started.
>
> Sometimes it drops me to the prom prompt. I am not very experienced so I was able only to find (ctrace) that
> the prompt was called in the method spwin_bad_ustack_from_kernel() which got there from mna_handler
> (misaligned access) through kernel_unaligned_trap(). I don't know which function triggered the
> unaligned access. The %o register values sent to the kernel_unaligned_trap() are outside addresses
> from System.map and outside addresses of loaded (or just loaded the sunlance) modules.
>
> This is where I need help. How can I find where the misaligned access happened?
>

The is a memory corruption issue on Sparc32 - sun4c (I am going to try and 
track it done over the next few days). It sounds like it may affect more 
than just sun4c issue.

Try going back to v2.6.22 and then appling 
f61698e6489f229f9fcfe29e68f228389a772993 - memset.S error, 
196bffa5dc3181897bd32e41415ec0db8dbab5e7 - entry.S delay loops,
f3c681c028846bd5d39f563909409832a295ca69 - Serial Console Locking

(My last working kernel is v2.6.22 Commit
eb6bf6bfb580afaf1e1a1d30cba17a078530cf4 with the first of the above two 
patches applied and some additional ones that fix verious sun 
partition/UFS filing sustem issues).

I am going to try to cherry pick a set of commits to see if I can't get a 
better idear of where the memory corruption on sun4c is coming from. Build 
problems sue to the DMA changes make git bisecting un-usable untill I have 
found out which patches fix the DMA build issues.

> Regards,
> Krzysztof
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Re: Sparc32 not working:2.6.23-rc1 (git commit 1e4dcd22efa7d24f637ab2ea3a77dd65774eb005)

[Adrian Bunk]

On Sun, Jul 29, 2007 at 07:26:29PM +0100, Mark Fortescue wrote:
>...
> I am going to try to cherry pick a set of commits to see if I can't get a 
> better idear of where the memory corruption on sun4c is coming from. Build 
> problems sue to the DMA changes make git bisecting un-usable untill I have 
> found out which patches fix the DMA build issues.

You have any known-good kernel?

Boot back into this kernel for bisecting and compiling the kernels for 
bisecting there.

cu
Adrian

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       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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Re: Sparc32 not working:2.6.23-rc1 (git commit 1e4dcd22efa7d24f637ab2ea3a77dd65774eb005)

[Mark Fortescue]

On Sun, 29 Jul 2007, Adrian Bunk wrote:

> On Sun, Jul 29, 2007 at 07:26:29PM +0100, Mark Fortescue wrote:
>> ...
>> I am going to try to cherry pick a set of commits to see if I can't get a
>> better idear of where the memory corruption on sun4c is coming from. Build
>> problems sue to the DMA changes make git bisecting un-usable untill I have
>> found out which patches fix the DMA build issues.
>
> You have any known-good kernel?
>
> Boot back into this kernel for bisecting and compiling the kernels for
> bisecting there.
>

As I said, bisecting does not work if you can't build the kernel because 
of un-defined symbols spanning most of the revisions you are interested 
in.

I have isolated the revisions that do not build so I should be able to 
cerry pick a commit/commits that fixes the build issues. Once done, I will 
be able to investigate the original issue.

If it were practical to do a build test on all supported platforms before 
submitting patches then this would not be so much of an issue but ...

> cu
> Adrian
>
> -- 
>
>       "Is there not promise of rain?" Ling Tan asked suddenly out
>        of the darkness. There had been need of rain for many days.
>       "Only a promise," Lao Er said.
>                                       Pearl S. Buck - Dragon Seed
>
> -
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