KASAN caught amdgpu / HMM use-after-free

[Jerome Glisse]

On Wed, Feb 27, 2019 at 06:02:49PM +0100, Michel Dänzer wrote:
> 
> See the attached dmesg excerpt. I've hit this a few times running piglit
> with amd-staging-drm-next, first on February 22nd.
> 
> The memory was freed after calling hmm_mirror_unregister in
> amdgpu_mn_destroy.

So that branch is not using the HMM changes queue up for 5.1 and thus
what you are doing is somewhat illegal. In 5.1 changes all is refcounted
and this bug should not be able to happen. So if you rebase your work
on top of 

https://cgit.freedesktop.org/~glisse/linux/log/?h=hmm-for-5.1

Or linux-next (i believe i saw those bits in linux-next) then this
error will vanish. Sorry if there was confusion between what is legal
now and what is legal tommorrow :)

Cheers,
Jérôme