Am 10.01.19 um 14:57 schrieb Christoph Hellwig:
On Thu, Jan 10, 2019 at 10:59:02AM +0100, Michel Dänzer wrote:
Hi Christoph,


https://bugs.freedesktop.org/109234 (please ignore comments #6-#9) was
bisected to your commit 55897af63091 "dma-direct: merge swiotlb_dma_ops
into the dma_direct code". Any ideas?
 From the trace it looks like we git the case where swiotlb tries
to copy back data from a bounce buffer, but hits a dangling or NULL
pointer.  So a couple questions for the submitter:

  - does the system have more than 4GB memory and thus use swiotlb?
    (check /proc/meminfo, and if something SWIOTLB appears in dmesg)
  - does the device this happens on have a DMA mask smaller than
    the available memory, that is should swiotlb be used here to start
    with?

Rather unlikely. The device is an AMD GPU, so we can address memory up to 1TB.

Christian.

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