[Bug 68171] [IVB/HSW ULT]system hang when run nightly testing

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=68171

--- Comment #9 from Ben Widawsky <ben at bwidawsk.net> ---
(In reply to comment #6)
> I dug a bit. It looks to me the failure is that pages is null here:
> 
> if (!obj->has_dma_mapping)
>         dma_unmap_sg(&dev->pdev->dev,
>                      obj->pages->sgl, obj->pages->nents,
>                      PCI_DMA_BIDIRECTIONAL);
> 
> 
> My disasm is a bit too complex to make sense out of at this hour.

I couldn't believe it before, but I did more digging, it seems to fail on:
obj->pages->nents, which at least on my compiled obj is done first.
 218a0:       49 8b 84 24 08 01 00    mov    0x108(%r12),%rax obj->pages
 218a7:       00
 218a8:       8b 50 08                mov    0x8(%rax),%edx obj->pages->nents
 218ab:       48 8b 30                mov    (%rax),%rsi
 218ae:       49 8b 85 90 04 00 00    mov    0x490(%r13),%rax // dev->pdev
 218b5:       48 89 c7                mov    %rax,%rdi
 218b8:       48 81 c7 98 00 00 00    add    $0x98,%rdi  //pdev->dev
(In reply to comment #6)

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