drm/amdgpu: dont schedule jobs while in reset

[Why]

doing kthread_park()/unpark() from drm_sched_entity_fini
while GPU reset is in progress defeats all the purpose of
drm_sched_stop->kthread_park.
If drm_sched_entity_fini->kthread_unpark() happens AFTER
drm_sched_stop->kthread_park nothing prevents from another
(third) thread to keep submitting job to HW which will be
picked up by the unparked scheduler thread and try to submit
to HW but fail because the HW ring is deactivated.

[How]
grab the reset lock before calling drm_sched_entity_fini()

Signed-off-by: Shirish S <shirish.s@amd.com>
Suggested-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -604,8 +604,11 @@ void amdgpu_ctx_mgr_entity_fini(struct amdgpu_ctx_mgr *mgr)
 			continue;
 		}
 
-		for (i = 0; i < num_entities; i++)
+		for (i = 0; i < num_entities; i++) {
+			mutex_lock(&ctx->adev->lock_reset);
 			drm_sched_entity_fini(&ctx->entities[0][i].entity);
+			mutex_unlock(&ctx->adev->lock_reset);
+		}
 	}
 }