[PATCH] drm/amdgpu: add rcu_barrier after entity fini

[Christian König]

Am 17.05.2018 um 05:05 schrieb Emily Deng:
> To free the fence from the amdgpu_fence_slab, need twice call_rcu, to avoid
> the amdgpu_fence_slab_fini call kmem_cache_destroy(amdgpu_fence_slab) before
> kmem_cache_free(amdgpu_fence_slab, fence), add rcu_barrier after drm_sched_entity_fini.
>
> The kmem_cache_free(amdgpu_fence_slab, fence)'s call trace as below:
> 1.drm_sched_entity_fini ->
> drm_sched_entity_cleanup ->
> dma_fence_put(entity->last_scheduled) ->
> drm_sched_fence_release_finished ->
> drm_sched_fence_release_scheduled ->
> call_rcu(&fence->finished.rcu, drm_sched_fence_free)
>
> 2.drm_sched_fence_free ->
> dma_fence_put(fence->parent) ->
> amdgpu_fence_release ->
> call_rcu(&f->rcu, amdgpu_fence_free) ->
> kmem_cache_free(amdgpu_fence_slab, fence);
>
> Change-Id: I8dcadd3372f97e72461bf46b41cc26d90f09b8df
> Signed-off-by: Emily Deng <Emily.Deng at amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 1 +
>   1 file changed, 1 insertion(+)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> index cc3b067..07b2e10 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> @@ -134,6 +134,7 @@ static void amdgpu_ttm_global_fini(struct amdgpu_device *adev)
>   	if (adev->mman.mem_global_referenced) {
>   		drm_sched_entity_fini(adev->mman.entity.sched,
>   				      &adev->mman.entity);
> +		rcu_barrier();

Good catch, but why don't you put the barrier() before the 
kmem_cache_destroy()?

That looks like it would make more sense.

Christian.

>   		mutex_destroy(&adev->mman.gtt_window_lock);
>   		drm_global_item_unref(&adev->mman.bo_global_ref.ref);
>   		drm_global_item_unref(&adev->mman.mem_global_ref);