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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D02E6C001DC for ; Wed, 19 Jul 2023 01:49:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229763AbjGSBtM (ORCPT ); Tue, 18 Jul 2023 21:49:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40468 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229574AbjGSBtK (ORCPT ); Tue, 18 Jul 2023 21:49:10 -0400 Received: from mail-qv1-xf33.google.com (mail-qv1-xf33.google.com [IPv6:2607:f8b0:4864:20::f33]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7618E1BF5 for ; Tue, 18 Jul 2023 18:49:03 -0700 (PDT) Received: by mail-qv1-xf33.google.com with SMTP id 6a1803df08f44-635ddf49421so29249426d6.2 for ; Tue, 18 Jul 2023 18:49:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; t=1689731342; x=1692323342; h=content-transfer-encoding:in-reply-to:from:references:cc:to :content-language:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=ePt0qbb27tTycT4WqVSlGhy/F+k69bMQ3wHHNqGkw8g=; b=ftucftlqM1A7m+5a0NUNMyV+yCtx/VHUnCHBo09FAO+BJiokRssGXbLclum0Rb7Vjw OF14yQ6yMnk28o83XcoVCyaGy9zhWUkZcamdMCbOWueKnvVfZG7kUvK3/73RvtuxhTEG 1qErlQtIZtTT2udV1v6oU6Iu+pwKvF9V5ODB8= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1689731342; x=1692323342; h=content-transfer-encoding:in-reply-to:from:references:cc:to :content-language:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=ePt0qbb27tTycT4WqVSlGhy/F+k69bMQ3wHHNqGkw8g=; b=dSNu1JNc6EZGLHpnbsXkStS8VV8E71Zh5e9xuHm3r1BaaALuHaIWiUcSEgBLGNyqCE pgF1TphOpYBOGr7zmoo5FBJGFZEl+DtxtcB5JzyPVEa4KU8NUj+Xc8z9zZwnwoTcl6T1 53xHKTs8Dq/3aIB+G0ntBtkvk6BlvC9gSBsCOds+4/4loS2QcE517PM2h0F/3fl+b1a/ W/VFg7UOXAahwtgIlobCYNR75LEWixLwMmnotSzNqbXx2LdrtXi9NSSj2AIfjWZ9JjoA MuufOKZK7eNP8Achi0dH/7TAdihvHfFl5W6B9qtcCjgALt4b5S4ekc3iyBDvS/3BExSp JcXg== X-Gm-Message-State: ABy/qLYnNtfvrw+pCuQczsNXM7K05AubvEMvTm5EFJd6MY5i/E+dVK5c /4k2l4VvFr/VXn7Vl9fKq1GO6A== X-Google-Smtp-Source: APBJJlEbQus1ueG5nPA4LisVdRCPwwlIEy0GOp7b9nLeIrxcSPFqAoKWGhXBDRtsYYeD/EHzxIsLsw== X-Received: by 2002:a0c:be88:0:b0:62d:ddeb:3782 with SMTP id n8-20020a0cbe88000000b0062dddeb3782mr13468345qvi.49.1689731342551; Tue, 18 Jul 2023 18:49:02 -0700 (PDT) Received: from [192.168.0.198] (c-98-249-43-138.hsd1.va.comcast.net. [98.249.43.138]) by smtp.gmail.com with ESMTPSA id t25-20020a0cb399000000b006238f82cde4sm1123436qve.108.2023.07.18.18.49.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 18 Jul 2023 18:49:00 -0700 (PDT) Message-ID: <449d0d48-ac98-659b-4d03-e75c318605d4@joelfernandes.org> Date: Tue, 18 Jul 2023 21:48:59 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Subject: Re: [PATCH rcu 6/6] rcu: Use WRITE_ONCE() for assignments to ->next for rculist_nulls Content-Language: en-US To: paulmck@kernel.org, Alan Huang Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org References: <6127192c-da9b-4599-9738-6e8f92e6c75c@paulmck-laptop> <20230717180317.1097590-6-paulmck@kernel.org> <9651c3b4-0791-5cd7-567f-f65d28bc8fae@joelfernandes.org> <3f6b04b3-af22-49f0-8d3c-269640f9f762@paulmck-laptop> From: Joel Fernandes In-Reply-To: <3f6b04b3-af22-49f0-8d3c-269640f9f762@paulmck-laptop> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/18/23 14:32, Paul E. McKenney wrote: > On Tue, Jul 18, 2023 at 10:48:07PM +0800, Alan Huang wrote: >> >>> 2023年7月18日 21:49，Joel Fernandes 写道： >>> >>> On 7/17/23 14:03, Paul E. McKenney wrote: >>>> From: Alan Huang >>>> When the objects managed by rculist_nulls are allocated with >>>> SLAB_TYPESAFE_BY_RCU, old readers may still hold references to an object >>>> even though it is just now being added, which means the modification of >>>> ->next is visible to readers. This patch therefore uses WRITE_ONCE() >>>> for assignments to ->next. >>>> Signed-off-by: Alan Huang >>>> Signed-off-by: Paul E. McKenney >>> >>> Did we ever conclude that the READ_ONCE() counterparts were not needed? ;-) >> >> Read-side is already protected by rcu_dereference_raw() in hlist_nulls_for_each_entry_{rcu, safe}. > > It turns out that different traversal synchronization designs want > different pointers using WRITE_ONCE(). Thank you Alan and Paul, Btw, I don't see any users of hlist_nulls_unhashed_lockless(), maybe it can be removed? - Joel