On 02.10.2012, at 23:43, Nishanth Aravamudan wrote:

Hi Ben,
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On 02.10.2012 [10:58:29 +1000], Benjamin Herrenschmidt wrote:

quoted

On Mon, 2012-10-01 at 16:03 +0200, Alexander Graf wrote:

quoted

Phew. Here we go :). It looks to be more of a PPC specific problem
than it appeared as at first:

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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.
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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.

=20
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")?
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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