From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CAB4BC77B73 for ; Thu, 27 Apr 2023 15:18:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244009AbjD0PSs (ORCPT ); Thu, 27 Apr 2023 11:18:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47758 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243404AbjD0PSr (ORCPT ); Thu, 27 Apr 2023 11:18:47 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DEBF24224; Thu, 27 Apr 2023 08:18:46 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 292AF63DF1; Thu, 27 Apr 2023 15:18:46 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D7954C433EF; Thu, 27 Apr 2023 15:18:43 +0000 (UTC) Date: Thu, 27 Apr 2023 11:18:42 -0400 From: Steven Rostedt To: Yafang Shao Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, kafai@fb.com, songliubraving@fb.com, yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com, haoluo@google.com, jolsa@kernel.org, mhiramat@kernel.org, bpf@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH bpf-next 5/6] bpf: Improve tracing recursion prevention mechanism Message-ID: <20230427111842.2e40fe3c@gandalf.local.home> In-Reply-To: References: <20230417154737.12740-1-laoar.shao@gmail.com> <20230417154737.12740-6-laoar.shao@gmail.com> <20230427092628.21fd23e4@gandalf.local.home> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-trace-kernel@vger.kernel.org On Thu, 27 Apr 2023 22:22:22 +0800 Yafang Shao wrote: > IIUC, the acquire/release pair works as follows, > > test_recursion_try_acquire > [ protection area ] > test_recursion_release > > After release, there will be no protection, and thus it will fail the > tools/testing/selftests/bpf/progs/recursion.c[1] test case, because > the recursion occurs in the bpf_prog_run() itself, But bpf programs are allowed to recurs. Hence, you need separate logic to detect that. The test_recursion_*() code is for cases that are not allowed to recurs. > > __bpf_prog_enter > test_recursion_try_acquire > [...] > test_recursion_release > // no protection after the release > bpf_prog_run() > bpf_prog_run() // the recursion can't be prevented. But I thought you can run a bpf_prog from another bpf_prog. So you don't want to prevent it. You need other logic to detect if it was not suppose to recurs. -- Steve > __bpf_prog_enter > test_recursion_try_acquire > [...] > test_recursion_release > bpf_prog_run() > bpf_prog_run() > __bpf_prog_enter > test_recursion_try_acquire > [...] > test_recursion_release > bpf_prog_run() > [ And so on ... ] > > [1]. https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/tools/testing/selftests/bpf/progs/recursion.c#n38