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=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 16DD1C433E6 for ; Mon, 1 Feb 2021 11:47:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C3E9264E9B for ; Mon, 1 Feb 2021 11:47:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229981AbhBALrg (ORCPT ); Mon, 1 Feb 2021 06:47:36 -0500 Received: from verein.lst.de ([213.95.11.211]:40808 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229481AbhBALre (ORCPT ); Mon, 1 Feb 2021 06:47:34 -0500 Received: by verein.lst.de (Postfix, from userid 2407) id 56C7C6736F; Mon, 1 Feb 2021 12:46:49 +0100 (CET) Date: Mon, 1 Feb 2021 12:46:49 +0100 From: Christoph Hellwig To: Miroslav Benes Cc: Christoph Hellwig , Frederic Barrat , Andrew Donnellan , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Daniel Vetter , Jessica Yu , Josh Poimboeuf , Jiri Kosina , Petr Mladek , Joe Lawrence , Masahiro Yamada , Michal Marek , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, dri-devel@lists.freedesktop.org, live-patching@vger.kernel.org, linux-kbuild@vger.kernel.org Subject: Re: [PATCH 04/13] module: use RCU to synchronize find_module Message-ID: <20210201114649.GA19696@lst.de> References: <20210128181421.2279-1-hch@lst.de> <20210128181421.2279-5-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 29, 2021 at 04:29:02PM +0100, Miroslav Benes wrote: > > > > - mutex_lock(&module_mutex); > > + rcu_read_lock_sched(); > > /* > > * We do not want to block removal of patched modules and therefore > > * we do not take a reference here. The patches are removed by > > @@ -74,7 +75,7 @@ static void klp_find_object_module(struct klp_object *obj) > > if (mod && mod->klp_alive) > > RCU always baffles me a bit, so I'll ask. Don't we need > rcu_dereference_sched() here? "mod" comes from a RCU-protected list, so I > wonder. rcu_dereference* is only used for dereferencing points where that reference itself is RCU protected, that is the lookup of mod itself down in find_module_all in this case. 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=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 78727C433DB for ; Mon, 1 Feb 2021 11:53:19 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 99BFB64DCC for ; Mon, 1 Feb 2021 11:53:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 99BFB64DCC Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4DTmY61CYVzDqJC for ; Mon, 1 Feb 2021 22:53:14 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=none (no SPF record) smtp.mailfrom=lst.de (client-ip=213.95.11.211; helo=verein.lst.de; envelope-from=hch@lst.de; receiver=) Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4DTmPy627NzDq8M for ; Mon, 1 Feb 2021 22:46:59 +1100 (AEDT) Received: by verein.lst.de (Postfix, from userid 2407) id 56C7C6736F; Mon, 1 Feb 2021 12:46:49 +0100 (CET) Date: Mon, 1 Feb 2021 12:46:49 +0100 From: Christoph Hellwig To: Miroslav Benes Subject: Re: [PATCH 04/13] module: use RCU to synchronize find_module Message-ID: <20210201114649.GA19696@lst.de> References: <20210128181421.2279-1-hch@lst.de> <20210128181421.2279-5-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Petr Mladek , Jiri Kosina , Andrew Donnellan , linux-kbuild@vger.kernel.org, David Airlie , Masahiro Yamada , Josh Poimboeuf , Maarten Lankhorst , linux-kernel@vger.kernel.org, Maxime Ripard , live-patching@vger.kernel.org, Michal Marek , Joe Lawrence , dri-devel@lists.freedesktop.org, Thomas Zimmermann , Jessica Yu , Frederic Barrat , Daniel Vetter , linuxppc-dev@lists.ozlabs.org, Christoph Hellwig Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Fri, Jan 29, 2021 at 04:29:02PM +0100, Miroslav Benes wrote: > > > > - mutex_lock(&module_mutex); > > + rcu_read_lock_sched(); > > /* > > * We do not want to block removal of patched modules and therefore > > * we do not take a reference here. The patches are removed by > > @@ -74,7 +75,7 @@ static void klp_find_object_module(struct klp_object *obj) > > if (mod && mod->klp_alive) > > RCU always baffles me a bit, so I'll ask. Don't we need > rcu_dereference_sched() here? "mod" comes from a RCU-protected list, so I > wonder. rcu_dereference* is only used for dereferencing points where that reference itself is RCU protected, that is the lookup of mod itself down in find_module_all in this case.