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SubjectRe: [PATCH 1/4] drm/v3d: Fix a use-after-free race accessing the scheduler's fences.
On Fri, 28 Sep 2018 16:21:23 -0700
Eric Anholt <eric@anholt.net> wrote:

> Once we push the job, the scheduler could run it and free it. So, if
> we want to reference their fences, we need to grab them before then.
> I haven't seen this happen in many days of conformance test runtime,
> but let's still close the race.
>
> Signed-off-by: Eric Anholt <eric@anholt.net>
> Fixes: 57692c94dcbe ("drm/v3d: Introduce a new DRM driver for Broadcom V3D V3.x+")

Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>

> ---
> drivers/gpu/drm/v3d/v3d_drv.h | 5 +++++
> drivers/gpu/drm/v3d/v3d_gem.c | 8 ++++++--
> 2 files changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/v3d/v3d_drv.h b/drivers/gpu/drm/v3d/v3d_drv.h
> index 5042573e97f4..83c55ab6e1c0 100644
> --- a/drivers/gpu/drm/v3d/v3d_drv.h
> +++ b/drivers/gpu/drm/v3d/v3d_drv.h
> @@ -204,6 +204,11 @@ struct v3d_exec_info {
> */
> struct dma_fence *bin_done_fence;
>
> + /* Fence for when the scheduler considers the render to be
> + * done, for when the BOs reservations should be complete.
> + */
> + struct dma_fence *render_done_fence;
> +
> struct kref refcount;
>
> /* This is the array of BOs that were looked up at the start of exec. */
> diff --git a/drivers/gpu/drm/v3d/v3d_gem.c b/drivers/gpu/drm/v3d/v3d_gem.c
> index e1fcbb4cd0ae..c98fbfbdb68e 100644
> --- a/drivers/gpu/drm/v3d/v3d_gem.c
> +++ b/drivers/gpu/drm/v3d/v3d_gem.c
> @@ -209,7 +209,7 @@ v3d_flush_caches(struct v3d_dev *v3d)
> static void
> v3d_attach_object_fences(struct v3d_exec_info *exec)
> {
> - struct dma_fence *out_fence = &exec->render.base.s_fence->finished;
> + struct dma_fence *out_fence = exec->render_done_fence;
> struct v3d_bo *bo;
> int i;
>
> @@ -409,6 +409,7 @@ v3d_exec_cleanup(struct kref *ref)
> dma_fence_put(exec->render.done_fence);
>
> dma_fence_put(exec->bin_done_fence);
> + dma_fence_put(exec->render_done_fence);
>
> for (i = 0; i < exec->bo_count; i++)
> drm_gem_object_put_unlocked(&exec->bo[i]->base);
> @@ -574,6 +575,9 @@ v3d_submit_cl_ioctl(struct drm_device *dev, void *data,
> if (ret)
> goto fail_unreserve;
>
> + exec->render_done_fence =
> + dma_fence_get(&exec->render.base.s_fence->finished);
> +
> kref_get(&exec->refcount); /* put by scheduler job completion */
> drm_sched_entity_push_job(&exec->render.base,
> &v3d_priv->sched_entity[V3D_RENDER]);
> @@ -587,7 +591,7 @@ v3d_submit_cl_ioctl(struct drm_device *dev, void *data,
> sync_out = drm_syncobj_find(file_priv, args->out_sync);
> if (sync_out) {
> drm_syncobj_replace_fence(sync_out,
> - &exec->render.base.s_fence->finished);
> + exec->render_done_fence);
> drm_syncobj_put(sync_out);
> }
>

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