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SubjectRe: [PATCH] swiotlb: Fix unexpected swiotlb_alloc_coherent() failures
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On 10/04/18 18:07, Takashi Iwai wrote:
> On Tue, 10 Apr 2018 19:06:15 +0200,
> Christoph Hellwig wrote:
>>
>> On Tue, Apr 10, 2018 at 07:05:13PM +0200, Takashi Iwai wrote:
>>> The code refactoring by commit 0176adb00406 ("swiotlb: refactor
>>> coherent buffer allocation") made swiotlb_alloc_buffer() almost always
>>> failing due to a thinko: namely, the function evaluates the
>>> dma_coherent_ok() call incorrectly and dealing as if it's invalid.
>>> This ends up with weird errors like iwlwifi probe failure or amdgpu
>>> screen flickering.
>>>
>>> This patch corrects the logic error.
>>
>> This looks ok, although even hitting this code is a bad sign. Do you
>> know why the previous dma_direct_alloc didn't succeed?
>
> That I have no idea, sorry. I just figured out the regression just
> from the dmesg output of 4.16 kernel in bugzilla reports.
> Could you take a look at the bugzilla reports there?

In the first one, the machine appears to have enough RAM that most of it
is beyond the device's 36-bit DMA mask, thus it's fairly likely for the
initial direct alloc to come back with something unsuitable.

Robin.

>
>
> thanks,
>
> Takashi
>
>>> Bugzilla: https://bugzilla.suse.com/show_bug.cgi?id=1088658
>>> Bugzilla: https://bugzilla.suse.com/show_bug.cgi?id=1088902
>>> Fixes: 0176adb00406 ("swiotlb: refactor coherent buffer allocation")
>>> Cc: <stable@vger.kernel.org> # v4.16+
>>> Signed-off-by: Takashi Iwai <tiwai@suse.de>
>>> ---
>>> lib/swiotlb.c | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/lib/swiotlb.c b/lib/swiotlb.c
>>> index 47aeb04c1997..de7cc540450f 100644
>>> --- a/lib/swiotlb.c
>>> +++ b/lib/swiotlb.c
>>> @@ -719,7 +719,7 @@ swiotlb_alloc_buffer(struct device *dev, size_t size, dma_addr_t *dma_handle,
>>> goto out_warn;
>>>
>>> *dma_handle = __phys_to_dma(dev, phys_addr);
>>> - if (dma_coherent_ok(dev, *dma_handle, size))
>>> + if (!dma_coherent_ok(dev, *dma_handle, size))
>>> goto out_unmap;
>>>
>>> memset(phys_to_virt(phys_addr), 0, size);
>>> --
>>> 2.16.3
>> ---end quoted text---
>>
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