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=-9.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 F2F92C433FF for ; Sun, 11 Aug 2019 22:11:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B82FE2085A for ; Sun, 11 Aug 2019 22:11:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="LxPn+Le8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726632AbfHKWLd (ORCPT ); Sun, 11 Aug 2019 18:11:33 -0400 Received: from mail-pl1-f196.google.com ([209.85.214.196]:46904 "EHLO mail-pl1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726592AbfHKWLc (ORCPT ); Sun, 11 Aug 2019 18:11:32 -0400 Received: by mail-pl1-f196.google.com with SMTP id c2so47115062plz.13 for ; Sun, 11 Aug 2019 15:11:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=qG6w/v4rW/drGrqs6yUqiBqNPa9XU08YuLl86izhqNc=; b=LxPn+Le8eqzU5KKEY65t0GCxNFrE9AW+SNsvBueI+tBYps6fhuqMVAQa0A/nf/JXQb v2qAw5F974OED/j2g4yc/OB55GwuXvT2GH/5F0WpRwK8aTnFXinwvFNzG4mxlN+cbrhT vqRePySZk3eRMBcu6T24hZV+fwW8rugvLaZMw= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=qG6w/v4rW/drGrqs6yUqiBqNPa9XU08YuLl86izhqNc=; b=asf1syaNLywQGW1l4QeRdJE/876z/sRCHnoPrDv86cSRMyCau/zJBRcUwQaZPvVrQx GKLbQbdGXtvedjd9s2tjp6zj0j2WE9Narno6H2Cy9foHWXJ/ntsmYxa0bmjleIXTpX1s fAjHp6jMX3p7ieUzBIg65I/FGQDbb8Nd3b/gZeZk08RrzuwU7PDwOh7NvU6WKtW4EjT/ S5e9y/36jAm2FKKb9QXdsPSNLd7AqIA8paPJiT2fFSIMLgPoimh6HkdX7VDCeiL5kdqp TCruMl+E7eqag5jTxmn437RvYHlUhFv6ja+ZY+SMZ5trMoTksYCD89esfNPrwoLZ9q3c S1Jg== X-Gm-Message-State: APjAAAUrvizB9k1Le+XjamCY1d8awkKzOMqY+i71tMU/AnisOTosjfVN dZGPtcJLimVsy7Sx1XBWFwhzY4R3ch4= X-Google-Smtp-Source: APXvYqz7AGfV2NJYXMolpML3Fs4JLGqvL7P3yYvhZ8O12EtndIT/TOTdXQUNnsEKVAL/HHKJmrNROg== X-Received: by 2002:a17:902:5983:: with SMTP id p3mr20650916pli.232.1565561491275; Sun, 11 Aug 2019 15:11:31 -0700 (PDT) Received: from joelaf.cam.corp.google.com ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id n10sm31376428pgv.67.2019.08.11.15.11.29 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Sun, 11 Aug 2019 15:11:30 -0700 (PDT) From: "Joel Fernandes (Google)" To: linux-kernel@vger.kernel.org Cc: "Joel Fernandes (Google)" , Greg Kroah-Hartman , Jonathan Corbet , Josh Triplett , Lai Jiangshan , linux-doc@vger.kernel.org, Mathieu Desnoyers , "Paul E. McKenney" , "Rafael J. Wysocki" , rcu@vger.kernel.org, Steven Rostedt , Tejun Heo Subject: [PATCH 2/3] doc: Update documentation about list_for_each_entry_rcu (v1) Date: Sun, 11 Aug 2019 18:11:10 -0400 Message-Id: <20190811221111.99401-2-joel@joelfernandes.org> X-Mailer: git-send-email 2.23.0.rc1.153.gdeed80330f-goog In-Reply-To: <20190811221111.99401-1-joel@joelfernandes.org> References: <20190811221111.99401-1-joel@joelfernandes.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This patch updates the documentation with information about usage of lockdep with list_for_each_entry_rcu(). Signed-off-by: Joel Fernandes (Google) --- Documentation/RCU/lockdep.txt | 15 +++++++++++---- Documentation/RCU/whatisRCU.txt | 9 ++++++++- 2 files changed, 19 insertions(+), 5 deletions(-) diff --git a/Documentation/RCU/lockdep.txt b/Documentation/RCU/lockdep.txt index da51d3068850..3d967df3a801 100644 --- a/Documentation/RCU/lockdep.txt +++ b/Documentation/RCU/lockdep.txt @@ -96,7 +96,14 @@ other flavors of rcu_dereference(). On the other hand, it is illegal to use rcu_dereference_protected() if either the RCU-protected pointer or the RCU-protected data that it points to can change concurrently. -There are currently only "universal" versions of the rcu_assign_pointer() -and RCU list-/tree-traversal primitives, which do not (yet) check for -being in an RCU read-side critical section. In the future, separate -versions of these primitives might be created. +Similar to rcu_dereference_protected, The RCU list and hlist traversal +primitives also check for whether there are called from within a reader +section. However, an optional lockdep expression can be passed to them as +the last argument in case they are called under other non-RCU protection. + +For example, the workqueue for_each_pwq() macro is implemented as follows. +It is safe to call for_each_pwq() outside a reader section but under protection +of wq->mutex: +#define for_each_pwq(pwq, wq) + list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node, + lock_is_held(&(wq->mutex).dep_map)) diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt index 17f48319ee16..cdd2a3e10e40 100644 --- a/Documentation/RCU/whatisRCU.txt +++ b/Documentation/RCU/whatisRCU.txt @@ -290,7 +290,7 @@ rcu_dereference() at any time, including immediately after the rcu_dereference(). And, again like rcu_assign_pointer(), rcu_dereference() is typically used indirectly, via the _rcu list-manipulation - primitives, such as list_for_each_entry_rcu(). + primitives, such as list_for_each_entry_rcu() [2]. [1] The variant rcu_dereference_protected() can be used outside of an RCU read-side critical section as long as the usage is @@ -305,6 +305,13 @@ rcu_dereference() a lockdep splat is emitted. See Documentation/RCU/Design/Requirements/Requirements.rst and the API's code comments for more details and example usage. + [2] In case the list_for_each_entry_rcu() primitive is intended + to be used outside of an RCU reader section such as when + protected by a lock, then an additional lockdep expression can be + passed as the last argument to it so that RCU lockdep checking code + knows that the dereference of the list pointers are safe. If the + indicated protection is not provided, a lockdep splat is emitted. + The following diagram shows how each API communicates among the reader, updater, and reclaimer. -- 2.23.0.rc1.153.gdeed80330f-goog