drm/amdgpu: make VMID assignment more fair v2

Similar to finding an idle one before reuse.

This guarantees fairness between processes. Otherwise process with a reserved
VMID have an unfair advantage while scheduling jobs.

v2: improve commit message

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Chunming Zhou <david1.zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -268,11 +268,6 @@ int amdgpu_vmid_grab(struct amdgpu_vm *vm, struct amdgpu_ring *ring,
 	int r = 0;
 
 	mutex_lock(&id_mgr->lock);
-	if (vm->reserved_vmid[vmhub]) {
-		r = amdgpu_vmid_grab_reserved_locked(vm, ring, sync, fence, job);
-		mutex_unlock(&id_mgr->lock);
-		return r;
-	}
 	fences = kmalloc_array(sizeof(void *), id_mgr->num_ids, GFP_KERNEL);
 	if (!fences) {
 		mutex_unlock(&id_mgr->lock);
@@ -319,6 +314,13 @@ int amdgpu_vmid_grab(struct amdgpu_vm *vm, struct amdgpu_ring *ring,
 	}
 	kfree(fences);
 
+	if (vm->reserved_vmid[vmhub]) {
+		r = amdgpu_vmid_grab_reserved_locked(vm, ring, sync,
+						     fence, job);
+		mutex_unlock(&id_mgr->lock);
+		return r;
+	}
+
 	job->vm_needs_flush = vm->use_cpu_for_update;
 	/* Check if we can use a VMID already assigned to this VM */
 	list_for_each_entry_reverse(id, &id_mgr->ids_lru, list) {