Messages in this thread | | | Date | Fri, 6 Feb 2009 08:08:12 -0800 | From | Chris Wright <> | Subject | Re: [PATCH 0/16] DMA-API debugging facility v2 |
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* David Woodhouse (dwmw2@infradead.org) wrote: > What machine did you get that on?
That's a T400 (I'd expect it's same issue as X200).
> Yeah, I saw one of those. If could be a driver bug, of course -- it > could be unmapping a range before it's actually finished with it. But > that's unlikely.
One thing I noticed is many of the faults are the page prior to a coherent range 0x8000 in length, which seems to correspond to tfd buffer. No obvious off-by-one error anywhere, and not all faults fit that pattern, so w/out more iwlagn driver knowledge hard to say if that's meaningful or just mapping coincidence.
> An alternative explanation... The DMA is aborted¹, and the device > interrupts us to tell us about it at the _same_ time that the IOMMU > interrupts us to tell us about the fault. We process the device > interrupt first, unmap that buffer. And then we process the IOMMU > interrupt... and the buffer is already gone from the list.
I'd have expected the iommu fault to be delivered first, but hey...
> It might be interesting to make this code also remember and print the > last range that was unmapped, as well as the currently-mapped ranges.
That's what I was thinking too. Almost need a flight recorder mode to see if the range was ever mapped/unmapped.
thanks, -chris -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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