On Mon, 14 Jan 2019 at 19:10, Christoph Hellwig <hch@xxxxxx> wrote:
>
> On Thu, Jan 10, 2019 at 06:52:26PM +0100, Sibren Vasse wrote:
> > On Thu, 10 Jan 2019 at 15:48, Christoph Hellwig <hch@xxxxxx> wrote:
> > >
> > > On Thu, Jan 10, 2019 at 03:00:31PM +0100, Christian König wrote:
> > > >> 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.
> > >
> > > So we probably somehow got a false positive.
> > >
> > > For now I'like the reported to confirm that the dma_direct_unmap_page+0x92
> > > backtrace really is in the swiotlb code (I can't think of anything else,
> > > but I'd rather be sure).
> > I'm not sure what you want me to confirm. Could you elaborate?
>
> Please open the vmlinux file for which this happend in gdb,
> then send the output from this command
>
> l *(dma_direct_unmap_page+0x92)
>
> to this thread.
My call trace contained:
Jan 10 16:34:51 <hostname> kernel: dma_direct_unmap_page+0x7a/0x80
(gdb) list *(dma_direct_unmap_page+0x7a)
0xffffffff810fa28a is in dma_direct_unmap_page (kernel/dma/direct.c:291).
286 size_t size, enum dma_data_direction dir,
unsigned long attrs)
287 {
288 phys_addr_t phys = dma_to_phys(dev, addr);
289
290 if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
291 dma_direct_sync_single_for_cpu(dev, addr, size, dir);
292
293 if (unlikely(is_swiotlb_buffer(phys)))
294 swiotlb_tbl_unmap_single(dev, phys, size, dir, attrs);
295 }
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