Re: amdgpu/TTM oopses since merging swiotlb_dma_ops into the dma_direct code

From: Christoph Hellwig <hch@lst.de>
To: Sibren Vasse <sibren@sibrenvasse.nl>
Cc: "Sibren Vasse" <freedesktop@sibrenvasse.nl>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
	"Michel Dänzer" <michel@daenzer.net>,
	x86@kernel.org, dri-devel@lists.freedesktop.org,
	christian.koenig@amd.com, iommu@lists.linux-foundation.org,
	amd-gfx@lists.freedesktop.org,
	"Robin Murphy" <robin.murphy@arm.com>,
	"Christoph Hellwig" <hch@lst.de>,
	"Marek Szyprowski" <m.szyprowski@samsung.com>
Subject: Re: amdgpu/TTM oopses since merging swiotlb_dma_ops into the dma_direct code
Date: Mon, 14 Jan 2019 19:10:41 +0100	[thread overview]
Message-ID: <20190114181041.GB8897@lst.de> (raw)
In-Reply-To: <CAF=iVcsEMfWyJck7RJ8-EGvKipXU=5eq3iv61mo49_7Wd4pHuw@mail.gmail.com>

On Thu, Jan 10, 2019 at 06:52:26PM +0100, Sibren Vasse wrote:
> On Thu, 10 Jan 2019 at 15:48, Christoph Hellwig <hch@lst.de> 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.

> > Second it would be great to print what the contents of io_tlb_start
> > and io_tlb_end are, e.g. by doing a printk_once in is_swiotlb_buffer,
> > maybe that gives a clue why we are hitting the swiotlb code here.
> 
> diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
> index 7c007ed7505f..042246dbae00 100644
> --- a/include/linux/swiotlb.h
> +++ b/include/linux/swiotlb.h
> @@ -69,6 +69,7 @@ extern phys_addr_t io_tlb_start, io_tlb_end;
> 
>  static inline bool is_swiotlb_buffer(phys_addr_t paddr)
>  {
> +    printk_once(KERN_INFO "io_tlb_start: %llu, io_tlb_end: %llu",
> io_tlb_start, io_tlb_end);
>      return paddr >= io_tlb_start && paddr < io_tlb_end;
>  }
> 
> Result on boot:
> [   11.405558] io_tlb_start: 3782983680, io_tlb_end: 3850092544

So this is a normal swiotlb location, and it does defintively exist.
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