[Bug 104082] amdgpu 0000:07:00.0: swiotlb buffer is full (sz: 2097152 bytes)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=104082

--- Comment #40 from Jean Delvare <jdelvare at suse.de> ---
I believe there are 2 incarnations of this bug, with the same symptoms but
different root causes.

The first bug is affecting kernels v4.14 and v4.15, it is caused by 2 MB
allocations failing too verbosely when in fact 4 kB allocations worked just
fine as a fallback. That one is fixed in v4.16 by:

commit d0bc0c2a31c95002d37c3cc511ffdcab851b3256
Author: Christian König
Date:   Thu Jan 4 14:24:19 2018 +0100

    swiotlb: suppress warning when __GFP_NOWARN is set

However kernel v4.16 also includes the following commit:

commit 0176adb004065d6815a8e67946752df4cd947c5b
Author: Christoph Hellwig
Date:   Tue Jan 9 22:15:30 2018 +0100

    swiotlb: refactor coherent buffer allocation

which contains a bug producing exactly the same backtraces. That bug is caused
by an improper check of the result of dma_coherent_ok(), which was fixed 10
days ago with:

commit 9e7f06c8beee304ee21b791653fefcd713f48b9a
Author: Takashi Iwai
Date:   Tue Apr 10 19:05:13 2018 +0200

    swiotlb: fix unexpected swiotlb_alloc_coherent failures

I backported this fix on top of v4.16.3 and the backtraces are gone. The commit
was tagged for stable inclusion so I expect it to be included in v4.16.

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