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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, 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 B0C9EC432C0 for ; Tue, 3 Dec 2019 13:41:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 93A312073F for ; Tue, 3 Dec 2019 13:41:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726363AbfLCNlf (ORCPT ); Tue, 3 Dec 2019 08:41:35 -0500 Received: from ms.lwn.net ([45.79.88.28]:52276 "EHLO ms.lwn.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725939AbfLCNlf (ORCPT ); Tue, 3 Dec 2019 08:41:35 -0500 Received: from lwn.net (localhost [127.0.0.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ms.lwn.net (Postfix) with ESMTPSA id 91DBC60B; Tue, 3 Dec 2019 13:41:33 +0000 (UTC) Date: Tue, 3 Dec 2019 06:41:32 -0700 From: Jonathan Corbet To: Amol Grover Cc: "Paul E . McKenney" , Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , rcu@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kernel-mentees@lists.linuxfoundation.org, Shuah Khan , Madhuparna Bhowmik Subject: Re: [PATCH] doc: listRCU: Add some more listRCU patterns in the kernel Message-ID: <20191203064132.38d75348@lwn.net> In-Reply-To: <20191203063941.6981-1-frextrite@gmail.com> References: <20191203063941.6981-1-frextrite@gmail.com> Organization: LWN.net MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8bit Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Tue, 3 Dec 2019 12:09:43 +0530 Amol Grover wrote: > - Add more information about listRCU patterns taking examples > from audit subsystem in the linux kernel. > > - The initially written audit examples are kept, even though they are > slightly different in the kernel. > > - Modify inline text for better passage quality. > > - Fix typo in code-blocks and improve code comments. > > - Add text formatting (italics, bold and code) for better emphasis. Thanks for improving the documentation! I'll leave the RCU stuff to the experts, but I do have one request... [...] > +When a process exits, ``release_task()`` calls ``list_del_rcu(&p->tasks)`` under > +``tasklist_lock`` writer lock protection, to remove the task from the list of > +all tasks. The ``tasklist_lock`` prevents concurrent list additions/removals > +from corrupting the list. Readers using ``for_each_process()`` are not protected > +with the ``tasklist_lock``. To prevent readers from noticing changes in the list > +pointers, the ``task_struct`` object is freed only after one or more grace > +periods elapse (with the help of ``call_rcu()``). This deferring of destruction > +ensures that any readers traversing the list will see valid ``p->tasks.next`` > +pointers and deletion/freeing can happen in parallel with traversal of the list. > +This pattern is also called an **existence lock**, since RCU pins the object in > +memory until all existing readers finish. Please don't put function names as literal text. If you just say call_rcu(), it will be formatted correctly and cross-linked to the appropriate kerneldoc entry. Saying ``call_rcu()`` defeats that and clutters the plain-text reading experience. Thanks, jon