Radeon R700 multi-ring bug

[Alex Deucher]

On Sat, Apr 19, 2014 at 5:54 AM, Christian König
<deathsimple at vodafone.de> wrote:
> Hi Marek,
>
> I've noticed this before as well, and I agree that it looks like a memory
> corruption. Not sure if the async DMA on the GPU or the CPU is overwriting
> something because of a race condition or something like this.
>
> Anyway, can you come up with a simple test case to reproduce the issue? For
> me it occurred only randomly while working on UVD support for R7xx. If you
> have something more reliable I could dig into it with my RV710.
>

Double check the code in the kernel that copies the IB from the user
copy to the kernel copy.  We had a bug when we first merged DMA
support where we weren't properly copying the across the IBs.  There
may still be a case where this is an issue:
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=de0babd60d8d43b58fd06a7803151d32cb589af0

Alex

> Christian.
>
> Am 19.04.2014 01:48, schrieb Marek Olšák:
>
>> Hi,
>>
>> If you submit a lot of graphics and DMA IBs interleaved, the graphics
>> CS checker sometimes fails with this message:
>>
>> [ 3846.435661] Forbidden register 0x0014 in cs at 9
>> [ 3846.435664] [drm:radeon_cs_ib_chunk] *ERROR* Invalid command stream !
>>
>> This error is only used for type-0 packets, but we don't use these
>> packets on R700 at all. Somehow, the graphics CS checker received
>> either the DMA IB or random garbage. My guess is there is memory
>> corruption happening during IB uploading and/or IB checking in the
>> kernel. Also, if you are unlucky, the GPU hangs instead.
>>
>> The CS thread offloading was disabled in Mesa, so the user space was
>> single-threaded.
>>
>> There are 2 ways to fix this:
>> - disable async DMA in Mesa
>> - call usleep(1) after the RADEON_CS ioctl returns
>>
>> This is just a heads-up. In the worst case, we can disable async DMA
>> for R700 in Mesa.
>>
>> Marek
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>
>
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