rcu_replace_pointer
struct dma_fence *old_ef = rcu_replace_pointer(*ef, new_ef, true
list = rcu_replace_pointer(dst->fences, list, dma_resv_held(dst));
old = rcu_replace_pointer(filp->pid, pid, 1);
engines_idle_release(ctx, rcu_replace_pointer(ctx->engines, NULL, 1));