linux-kernel - Re: Bad rss-counter state from drm/ttm, drm/vmwgfx: Support huge TTM pagefaults

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Date:   Tue, 7 Apr 2020 21:57:27 +0200
From:   Thomas Hellström (VMware) 
        <thomas_os@...pmail.org>
To:     "Alex Xu (Hello71)" <alex_y_xu@...oo.ca>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Christian König <christian.koenig@....com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-graphics-maintainer@...are.com,
        Michal Hocko <mhocko@...e.com>, pv-drivers@...are.com,
        Ralph Campbell <rcampbell@...dia.com>,
        Roland Scheidegger <sroland@...are.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>
Subject: Re: Bad rss-counter state from drm/ttm, drm/vmwgfx: Support huge TTM
 pagefaults

On 4/7/20 5:36 PM, Alex Xu (Hello71) wrote:
> Excerpts from Thomas Hellström (VMware)'s message of April 7, 2020 7:26 am:
>> On 4/7/20 2:38 AM, Alex Xu (Hello71) wrote:
>>> Excerpts from Thomas Hellström (VMware)'s message of April 6, 2020 5:04 pm:
>>>> Hi,
>>>>
>>>> On 4/6/20 9:51 PM, Alex Xu (Hello71) wrote:
>>>>> Using 314b658 with amdgpu, starting sway and firefox causes "BUG: Bad
>>>>> rss-counter state" and "BUG: non-zero pgtables_bytes on freeing mm" to
>>>>> start filling dmesg, and then closing programs causes more BUGs and
>>>>> hangs, and then everything grinds to a halt (can't start more programs,
>>>>> can't even reboot through systemd).
>>>>>
>>>>> Using master and reverting that branch up to that point fixes the
>>>>> problem.
>>>>>
>>>>> I'm using a Ryzen 1600 and AMD Radeon RX 480 on an ASRock B450 Pro4
>>>>> board with IOMMU enabled.
>>>> If you could try the attached patch, that'd be great!
>>>>
>>>> Thanks,
>>>>
>>>> Thomas
>>>>
>>> Yeah, that works too. Kernel config sent off-list.
>>>
>>> Regards,
>>> Alex.
>> Thanks. Do you want me to add your
>>
>> Reported-by: and Tested-by: To this patch?
>>
>> /Thomas
>>
>>
> Sure. Shouldn't we fix it properly though?

It's still enabled for vmwgfx for which it is reasonably well tested and 
where I can't see any such errors.

The code we remove with this patch enables huge page-table entries in 
some circumstances for other drivers, but given the problems you're 
seeing for amdgpu, it's better to enable this on a per-driver basis 
after thorough testing. Since I don't have amdgpu hardware I'm not sure 
what it's doing differently, and can't debug the issue properly.

/Thomas