[linux.git drm/ttm]: NULL pointer dereference upon driver probe

[Tetsuo Handa]

On 2020/08/07 0:39, Daniel Vetter wrote:
> On Thu, Aug 6, 2020 at 5:28 PM Christian König <christian.koenig at amd.com> wrote:
>>
>> My best guess is that you are facing two separate bugs here.
>>
>> Crash #1 is somehow related to CRTCs and might even be cause by the
>> atomic-helper change you noted below.
> 
> Yeah, and I think I know what's going on. Patch incoming. When testing
> that patch, please make sure you're testing on a kernel with shows
> crash pattern 1, but is not broken by crash pattern 2.
> -Daniel

I confirmed that the patch at https://lkml.kernel.org/r/20200806154227.2255197-1-daniel.vetter@ffwll.ch
changes crash pattern from 1 to 2. You can send the patch for avoiding Crash #1.

> 
>>
>> Crash #2 is caused because vmw_bo_create_and_populate() tries to
>> manually populate a BO object instead of relying on TTM to do it when
>> necessary. This indeed doesn't work any more because of "drm/ttm: make
>> TT creation purely optional v3".
>>
>> Question is why vmwgfx is doing this?
>>
>> Regards,
>> Christian.
>>

F.Y.I. syzbot is reporting a similar NULL pointer dereference on virtio at 
https://syzkaller.appspot.com/bug?id=955763105a919df5d19b8ed26f244d698ef15ac3 .
Bisection attempt is not made yet because reproducer is not found yet.