Use after free from intel_alloc_iova

[Chris Wilson]

Quoting Lu Baolu (2019-06-22 07:49:22)
> Hi Chris,
> 
> Thanks for the test and report.
> 
> On 6/21/19 9:27 PM, Chris Wilson wrote:
> > We see a use-after-free in our CI about 20% of the time on a Skylake
> > iommu testing host, present since enabling that host. Sadly, it has not
> > presented itself while running under KASAN.
> > 
> > <4> [302.391799] general protection fault: 0000 [#1] PREEMPT SMP PTI
> > <4> [302.391803] CPU: 7 PID: 4854 Comm: i915_selftest Tainted: G     U            5.2.0-rc5-CI-CI_DRM_6320+ #1
> 
> Since it's CI-CI_DRM_6320+, what kind of patches have you applied on top
> of 5.2.0-rc5?

$ git diff --stat v5.2-rc5..intel/CI_DRM_6320
...
1383 files changed, 62481 insertions(+), 35301 deletions(-)

The usual drivers/gpu churn, and nothing inside drivers/iommu.

Our oldest report (when the machine was configured) was with
4.19.0-CI-CI_DRM_5049. The tags are available from
git://git.freedesktop.org/git/gfx-ci/linux
-Chris