From patchwork Fri Jul 12 17:00:24 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Joel Fernandes X-Patchwork-Id: 11042599 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id CFFD0138D for ; Fri, 12 Jul 2019 17:02:22 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id B94691FFFF for ; Fri, 12 Jul 2019 17:02:22 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id ACB5928B47; Fri, 12 Jul 2019 17:02:22 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.wl.linuxfoundation.org (Postfix) with SMTP id C54D127D0C for ; Fri, 12 Jul 2019 17:02:21 +0000 (UTC) Received: (qmail 5132 invoked by uid 550); 12 Jul 2019 17:01:24 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 4016 invoked from network); 12 Jul 2019 17:01:23 -0000 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=/5hJQY7vBLoyimOM3U70MNxFgsc86oXhHYtdVzU5ujQ=; b=UAjbMqka7p1GCxFlNusyg29g1RCPFz9WIMtWvkN7qrcNF+ATnO9YKmLvPnuqPRJWG8 01CXWPFPyGYm3lOSoebpREdMbvmnc55dMqjKROvd/t5QxrZ6o7iZwPGUGOYk4Ll55hdr IVAnsP7Rq6Ff+RAPzreODHBCQNzqAghR4nuBM= 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=/5hJQY7vBLoyimOM3U70MNxFgsc86oXhHYtdVzU5ujQ=; b=U7gRm+Tuei03oatPJKMSMRBPq+qdQn0jsZlDVDZQf48OR6yeyvcUo3B64KtTWw9UXi 2ElqmAa1ZGs8v7CcNidLi6LpBfFnvel/ZI4KUEF1sjFbN6brggPbXB1aQskhOCj0ROrp shO+14gZTAOncwYB/Gz1+thzenq/9iyi7lkyHgoO8e1yyVKJ+vFuLu2vJbZAgfpHNp2D sO87IIkIHjTGnOWEFH0gpwMclmcmfw8WSQmvTwbNyqRQZPhyJk3kcVpCL8OgkRJ21hE7 wzxmcNHFukwGyaERxclOztrbr61jFijwe/DKbNKlg8tjuI9nb8BkY3UCoNyLnF4FHqRL QS/w== X-Gm-Message-State: APjAAAX3/gb5GrmntjZ2SDV/mnermGPTfobcOsBVPqXpFXUI2LIsAzzZ KPb6XnsK0mSEcB4czyh1WMU= X-Google-Smtp-Source: APXvYqysKQjlbPJnzD1SgXu0qrPOgUWrpmjWhJmLr3dLME/oF4p6YcJaiWDgGdC5pNxKNHie+MpwEA== X-Received: by 2002:a63:dc56:: with SMTP id f22mr12036675pgj.305.1562950871565; Fri, 12 Jul 2019 10:01:11 -0700 (PDT) From: "Joel Fernandes (Google)" To: linux-kernel@vger.kernel.org Cc: "Joel Fernandes (Google)" , Alexey Kuznetsov , Bjorn Helgaas , Borislav Petkov , c0d1n61at3@gmail.com, "David S. Miller" , edumazet@google.com, Greg Kroah-Hartman , Hideaki YOSHIFUJI , "H. Peter Anvin" , Ingo Molnar , Jonathan Corbet , Josh Triplett , keescook@chromium.org, kernel-hardening@lists.openwall.com, kernel-team@android.com, Lai Jiangshan , Len Brown , linux-acpi@vger.kernel.org, linux-doc@vger.kernel.org, linux-pci@vger.kernel.org, linux-pm@vger.kernel.org, Mathieu Desnoyers , neilb@suse.com, netdev@vger.kernel.org, Oleg Nesterov , "Paul E. McKenney" , Pavel Machek , peterz@infradead.org, "Rafael J. Wysocki" , Rasmus Villemoes , rcu@vger.kernel.org, Steven Rostedt , Tejun Heo , Thomas Gleixner , will@kernel.org, x86@kernel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)) Subject: [PATCH v2 9/9] doc: Update documentation about list_for_each_entry_rcu Date: Fri, 12 Jul 2019 13:00:24 -0400 Message-Id: <20190712170024.111093-10-joel@joelfernandes.org> X-Mailer: git-send-email 2.22.0.510.g264f2c817a-goog In-Reply-To: <20190712170024.111093-1-joel@joelfernandes.org> References: <20190712170024.111093-1-joel@joelfernandes.org> MIME-Version: 1.0 X-Virus-Scanned: ClamAV using ClamSMTP 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 981651a8b65d..a08c03735963 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 RCU/Design/Requirements/Requirements.html 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.