amdgpu_bo_destroy had a bug by calling amdgpu_bo_unref outside mutex_lock.
If amdgpu_device_recover_vram executed between amdgpu_bo_unref and 
list_del_init,
it would get NULL of shadow->parent, then caused Call Trace and GPU reset 
failed.

Change-Id: I41d7b54605e613e87ee03c3ad89c191063c19230
Signed-off-by: Wentao Lou <wentao....@amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_object.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
index ec9e450..93b2c5a 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
@@ -88,12 +88,14 @@ static void amdgpu_bo_destroy(struct ttm_buffer_object *tbo)
        if (bo->gem_base.import_attach)
                drm_prime_gem_destroy(&bo->gem_base, bo->tbo.sg);
        drm_gem_object_release(&bo->gem_base);
-       amdgpu_bo_unref(&bo->parent);
+       /* in case amdgpu_device_recover_vram got NULL of bo->parent */
        if (!list_empty(&bo->shadow_list)) {
                mutex_lock(&adev->shadow_list_lock);
                list_del_init(&bo->shadow_list);
                mutex_unlock(&adev->shadow_list_lock);
        }
+       amdgpu_bo_unref(&bo->parent);
+
        kfree(bo->metadata);
        kfree(bo);
 }
-- 
2.7.4

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