[PATCH] Revert "drm/amdgpu: Use dma_buf from GEM object instance"

[Thomas Zimmermann]

This reverts commit 515986100d176663d0a03219a3056e4252f729e6.

The dma_buf field in struct drm_gem_object is not stable over the
object instance's lifetime. The field becomes NULL when user space
releases the final GEM handle on the buffer object. This resulted
in a NULL-pointer deref.

Workarounds in commit 5307dce878d4 ("drm/gem: Acquire references on
GEM handles for framebuffers") and commit f6bfc9afc751 ("drm/framebuffer:
Acquire internal references on GEM handles") only solved the problem
partially. They especially don't work for buffer objects without a DRM
framebuffer associated.

Hence, this revert to going back to using .import_attach->dmabuf.

Signed-off-by: Thomas Zimmermann <tzimmerm...@suse.de>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c | 2 +-
 drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c     | 3 ++-
 drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c      | 2 +-
 3 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
index ff98c87b2e0b..5743ebb2f1b7 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
@@ -514,7 +514,7 @@ bool amdgpu_dmabuf_is_xgmi_accessible(struct amdgpu_device 
*adev,
                return false;
 
        if (drm_gem_is_imported(obj)) {
-               struct dma_buf *dma_buf = obj->dma_buf;
+               struct dma_buf *dma_buf = obj->import_attach->dmabuf;
 
                if (dma_buf->ops != &amdgpu_dmabuf_ops)
                        /* No XGMI with non AMD GPUs */
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
index 6626a6e64ff5..d1ccbfcf21fa 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
@@ -317,7 +317,8 @@ static int amdgpu_gem_object_open(struct drm_gem_object 
*obj,
         */
        if (!vm->is_compute_context || !vm->process_info)
                return 0;
-       if (!drm_gem_is_imported(obj) || !dma_buf_is_dynamic(obj->dma_buf))
+       if (!drm_gem_is_imported(obj) ||
+           !dma_buf_is_dynamic(obj->import_attach->dmabuf))
                return 0;
        mutex_lock_nested(&vm->process_info->lock, 1);
        if (!WARN_ON(!vm->process_info->eviction_fence)) {
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
index af0f655dfd5b..b9b4f7d9186e 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
@@ -1272,7 +1272,7 @@ int amdgpu_vm_bo_update(struct amdgpu_device *adev, 
struct amdgpu_bo_va *bo_va,
                struct drm_gem_object *obj = &bo->tbo.base;
 
                if (drm_gem_is_imported(obj) && bo_va->is_xgmi) {
-                       struct dma_buf *dma_buf = obj->dma_buf;
+                       struct dma_buf *dma_buf = obj->import_attach->dmabuf;
                        struct drm_gem_object *gobj = dma_buf->priv;
                        struct amdgpu_bo *abo = gem_to_amdgpu_bo(gobj);
 
-- 
2.50.0