On 02.10.2012, at 23:43, Nishanth Aravamudan wrote:
> Hi Ben,
>
> On 02.10.2012 [10:58:29 +1000], Benjamin Herrenschmidt wrote:
>> On Mon, 2012-10-01 at 16:03 +0200, Alexander Graf wrote:
>>> Phew. Here we go :). It looks to be more of a PPC specific problem
>>> than it appeared as at first:
>>
>> Ok, so I suspect the problem is the pushing down of the locks which
>> breaks with iommu backends that have a separate flush callback. In
>> that case, the flush moves out of the allocator lock.
>>
>> Now we do call flush before we return, still, but it becomes racy
>> I suspect, but somebody needs to give it a closer look. I'm hoping
>> Anton or Nish will later today.
>
> Started looking into this. If your suspicion were accurate, wouldn't the
> bisection have stopped at 0e4bc95d87394364f408627067238453830bdbf3
> ("powerpc/iommu: Reduce spinlock coverage in iommu_alloc and
> iommu_free")?
>
> Alex, the error is reproducible, right?
Yes. I'm having a hard time to figure out if the reason my U4 based G5 Mac crashes and fails reading data is the same since I don't have a serial connection there, but I assume so.
> Does it go away by reverting
> that commit against mainline? Just trying to narrow down my focus.
The patch doesn't revert that easily. Mind to provide a revert patch so I can try?
Alex
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