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 X-Spam-Level: X-Spam-Status: No, score=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 65190C32771 for ; Mon, 13 Jan 2020 03:16:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 38C3421556 for ; Mon, 13 Jan 2020 03:16:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578885406; bh=3zYO/LV7CNbRZmQEB1qLQGLItuEsGDzoXBLkzEVNe2c=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=mdJbYFnJlRCAsaZWAG1QwJx7nHZnzXFtpV5bOI4lWnqmNVMVfH9TqLZheLorWwohE vC0RbTFzPYACqCnqDl37gDEPHUWVFLMXFoc/ox0Pvx6j91FO0tCBtIoNDE4VlBgCCo lnrC5KsMUCmg6oO80LsaOCSu2RYhMGdiVSnPrxso= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733142AbgAMDQp (ORCPT ); Sun, 12 Jan 2020 22:16:45 -0500 Received: from mail.kernel.org ([198.145.29.99]:54826 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732961AbgAMDQp (ORCPT ); Sun, 12 Jan 2020 22:16:45 -0500 Received: from devnote2 (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B025721556; Mon, 13 Jan 2020 03:16:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578885404; bh=3zYO/LV7CNbRZmQEB1qLQGLItuEsGDzoXBLkzEVNe2c=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=RCdMxJUOUJEUP6ZUIV4gkd0trBnyqFBTGpbWavtcwtLwkOB8MXaEFeJ3rAwHW6SAh BVmV/1FnfE9vhJDJtPEo1A9BwKoH+PYD0Ob2nYi3IxYH3Er8nN1pKfhOde6flu8GYe dY1HHkqDJzlAqqI0qXTA6vhjyBUAPpyuDy0P0A/Q= Date: Mon, 13 Jan 2020 12:16:40 +0900 From: Masami Hiramatsu To: Joel Fernandes Cc: Ingo Molnar , Anders Roxell , paulmck@kernel.org, "Naveen N . Rao" , Anil S Keshavamurthy , David Miller , Linux Kernel Mailing List Subject: Re: [PATCH -tip V2 0/2] kprobes: Fix RCU warning and cleanup Message-Id: <20200113121640.bfab48c105dae9b1918c2d82@kernel.org> In-Reply-To: <20200112020537.GJ128013@google.com> References: <157535316659.16485.11817291759382261088.stgit@devnote2> <20191221035541.69fc05613351b8dabd6e1a44@kernel.org> <20200107211535.233e7ff396f867ee1348178b@kernel.org> <20200110211438.GE128013@google.com> <20200111083507.c32b85b1d47aa69928de530b@kernel.org> <20200112020537.GJ128013@google.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 11 Jan 2020 21:05:37 -0500 Joel Fernandes wrote: > On Sat, Jan 11, 2020 at 08:35:07AM +0900, Masami Hiramatsu wrote: > > Hi Joel and Paul, > > > > On Fri, 10 Jan 2020 16:14:38 -0500 > > Joel Fernandes wrote: > > > > > On Tue, Jan 07, 2020 at 09:15:35PM +0900, Masami Hiramatsu wrote: > > > > Hello, > > > > > > > > Anyone have any comment on this series? > > > > Without this series, I still see the suspicious RCU warning for kprobe on -tip tree. > > > > > > +Paul since RCU. > > > > > > Hi Masami, > > > > > > I believe I had commented before that I don't agree with this patch: > > > https://lore.kernel.org/lkml/157535318870.16485.6366477974356032624.stgit@devnote2/ > > > > > > The rationale you used is to replace RCU-api with non-RCU api just to avoid > > > warnings. I think a better approach is to use RCU api and pass the optional > > > expression to silence the false-positive warnings by informing the RCU API > > > about the fact that locks are held (similar to what we do for > > > rcu_dereference_protected()). The RCU API will do additional checking > > > (such as making sure preemption is disabled for safe RCU usage etc) as well. > > > > Yes, that is what I did in [1/2] for get_kprobe(). > > Let me clarify the RCU list usage in [2/2]. > > > > With the careful check, other list traversals never be done in non-sleepable > > context, those are always runs with kprobe_mutex held. > > If I correctly understand the Documentation/RCU/listRCU.rst, we should/can use > > non-RCU api for those cases, or do I miss something? > > Yes, that is fine. However personally I prefer not to mix usage of > list_for_each_entry_rcu() and list_for_each_entry() on the same pointer > (kprobe_table). I think it is more confusing and error prone. Just use > list_for_each_entry_rcu() everywhere and pass the appropriate lockdep > expression, instead of calling lockdep_assert_held() independently. Is this > not doable? Hmm, but isn't it more confusing that user just take a mutex but no rcu_read_lock() with list_for_each_entry_rcu()? In that case, sometimes it might sleep inside list_for_each_entry_rcu(), I thought that might be more confusing mind model for users... Anyway, if so, please update Documentation/RCU/listRCU.rst too. Thank you, -- Masami Hiramatsu