drm/amdgpu: minor PRT turnoff fix (v2)

When two VMs stop using PRT support at the same time we might
not disable it in the right order otherwise.

v2: agd: rebase
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c

@@ -1200,6 +1200,7 @@ static void amdgpu_vm_prt_cb(struct dma_fence *fence, struct dma_fence_cb *_cb)
 {
 	struct amdgpu_prt_cb *cb = container_of(_cb, struct amdgpu_prt_cb, cb);
 
+	if (atomic_dec_return(&cb->adev->vm_manager.num_prt_mappings) == 0)
 		amdgpu_vm_update_prt_state(cb->adev);
 	kfree(cb);
 }
@@ -1219,17 +1220,14 @@ static void amdgpu_vm_free_mapping(struct amdgpu_device *adev,
 				   struct amdgpu_bo_va_mapping *mapping,
 				   struct dma_fence *fence)
 {
-	if ((mapping->flags & AMDGPU_PTE_PRT) &&
-	    atomic_dec_return(&adev->vm_manager.num_prt_mappings) == 0) {
+	if (mapping->flags & AMDGPU_PTE_PRT) {
 		struct amdgpu_prt_cb *cb = kmalloc(sizeof(struct amdgpu_prt_cb),
 						   GFP_KERNEL);
 
 		cb->adev = adev;
 		if (!fence || dma_fence_add_callback(fence, &cb->cb,
-						     amdgpu_vm_prt_cb)) {
-			amdgpu_vm_update_prt_state(adev);
-			kfree(cb);
-		}
+						     amdgpu_vm_prt_cb))
+			amdgpu_vm_prt_cb(fence, &cb->cb);
 	}
 	kfree(mapping);
 }