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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3B587CFB43F for ; Mon, 7 Oct 2024 14:54:14 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C5D3F6B00A8; Mon, 7 Oct 2024 10:54:13 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C0DF96B00A9; Mon, 7 Oct 2024 10:54:13 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AD5406B00AA; Mon, 7 Oct 2024 10:54:13 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 8D63F6B00A8 for ; Mon, 7 Oct 2024 10:54:13 -0400 (EDT) Received: from smtpin24.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 3A16C805B3 for ; Mon, 7 Oct 2024 14:54:13 +0000 (UTC) X-FDA: 82647101586.24.A583228 Received: from smtpout.efficios.com (smtpout.efficios.com [167.114.26.122]) by imf02.hostedemail.com (Postfix) with ESMTP id 7E37B80022 for ; Mon, 7 Oct 2024 14:54:11 +0000 (UTC) Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=efficios.com header.s=smtpout1 header.b=VVbZsMaT; spf=pass (imf02.hostedemail.com: domain of mathieu.desnoyers@efficios.com designates 167.114.26.122 as permitted sender) smtp.mailfrom=mathieu.desnoyers@efficios.com; dmarc=pass (policy=none) header.from=efficios.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1728312783; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=v2f3AhNnxU8jk79l5HhdM4G0X6TGFVxBdNyUOHNDEUI=; b=naHSSpJqeYUA/065B6hGzHkdvrIPap/hRHCWACP8ahpWBCD4KQF2nL4d5bL1j6THJPCl8Q LTkbFWD5wOChX+so+PQ3+bvsq1o27UjAOERVMDI70OHHsX1vavoDzmLqpGjNguAoLZTvDV WoxzYaKSCgp0gOcBDWDmfQKvFL+Aqw4= ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=pass header.d=efficios.com header.s=smtpout1 header.b=VVbZsMaT; spf=pass (imf02.hostedemail.com: domain of mathieu.desnoyers@efficios.com designates 167.114.26.122 as permitted sender) smtp.mailfrom=mathieu.desnoyers@efficios.com; dmarc=pass (policy=none) header.from=efficios.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1728312783; a=rsa-sha256; cv=none; b=q8bigIVvfxYkL5tSsac2qSkwpbYeHZtCPguVs2WPqyH0+Aht//abX6D4zEuV96AdFwbEbt mriAZG6+V9L+TlOazMQHRbZzM1z28Qh8Whabr3u53Vt9zsRBKzR5A4hqQf2PkpXYG1ILc3 7nyXyETqHcPlDbtDVwal0u0DdY/i/Fg= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=efficios.com; s=smtpout1; t=1728312850; bh=sihbyG/v8McdrExFlMF4l5W4opSu7i5ut7iK0mpnEh8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=VVbZsMaTm+kJ+mJ61HRGRpZ1hTwl6/ALHHgD0lC47SzwRONtiKJDP/owbxPIJ+I1t GYhhI0in/OnM8yY6y+4C4JufX3rNF6tnmGUFxS34BeyhyE4zscpqNdh/LogWI9pG70 j7L26qV3xBABIsUZOHvjrGFRO/NKwbYhUdT9Bg8wzlnGYm4eq7ZMhreaqgZ1t9JqhX E6ucijPLbq5BlRs+yPP4gInxeIHHwJgDBxfmhI4Kk346JdqkkhEI72IFYXlFwpZ3eZ e9hEEOIF9AqQSTpznimryYAmopYOU4GA1EUTF/ZNC0QBOGBsCgbfUz45hQ6ici00a3 dnk+p+fdadBCQ== Received: from [172.16.0.134] (96-127-217-162.qc.cable.ebox.net [96.127.217.162]) by smtpout.efficios.com (Postfix) with ESMTPSA id 4XMhxZ2Smtz3DX; Mon, 7 Oct 2024 10:54:10 -0400 (EDT) Message-ID: Date: Mon, 7 Oct 2024 10:52:12 -0400 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 3/4] hp: Implement Hazard Pointers To: Boqun Feng Cc: Linus Torvalds , Andrew Morton , Peter Zijlstra , linux-kernel@vger.kernel.org, Nicholas Piggin , Michael Ellerman , Greg Kroah-Hartman , Sebastian Andrzej Siewior , "Paul E. McKenney" , Will Deacon , Alan Stern , John Stultz , Neeraj Upadhyay , Frederic Weisbecker , Joel Fernandes , Josh Triplett , Uladzislau Rezki , Steven Rostedt , Lai Jiangshan , Zqiang , Ingo Molnar , Waiman Long , Mark Rutland , Thomas Gleixner , Vlastimil Babka , maged.michael@gmail.com, Mateusz Guzik , Jonas Oberhauser , rcu@vger.kernel.org, linux-mm@kvack.org, lkmm@lists.linux.dev References: <20241002010205.1341915-1-mathieu.desnoyers@efficios.com> <20241002010205.1341915-4-mathieu.desnoyers@efficios.com> From: Mathieu Desnoyers Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: 7E37B80022 X-Stat-Signature: 5gzt9gcphnu3sj9nikeh6ha8yq45ghq9 X-HE-Tag: 1728312851-461640 X-HE-Meta: U2FsdGVkX1+TsTJBvgZC5ebCPZljumEgsWrHnFIZi0Nt7QrF0mKbhRMDSZzEZhYLI+zv4xn7MOxZX36iiDjr4ghW1adDfrzU16tzHzZHacr0i1OBufq8YAlXbR6VLly2XgvCg5QeiNevRaHgfoK9NLp0hVCVkyG8kVFRDgRcfKwUq03JrjoGwoYhdcZoGMyKIj3kru6FlYWBDOhYojGybO3Wrgl8AUCFvGu93YBoONKYigpJeix4yumAXq3KPrO24KG+sC2l1qsliDqSRgO4CrnvTHqr5qiIdEmM5kOxLRbbwo89XA6HUAONtN5/pmCttbHZU+jl53Swxdszty8C09I/YMaZzMU3P55KbwkDrh7mE8buxm+Z7Qk2lJW1A2ltJGVg1kC/Oz69t/LYRjvw+VSkL5XSR01z+erhKIgzOAUPfKlCpvFUDjkij0Ir4+WbpfaUzpVG/sdKj/oFXS2fkIpcYNAHg+L0IhljyV6e/B64ZUw8tIX8ENtkBifHR+Mzm/v/QHjwINCce/oDm9KSXtsTHLq+kktIhTbEawG77HVspyL673+/fp7XdqrbqgQJKiHe0ihw/4gaBtPc2NBlBg8XMlhZi0K35srlxNzAQrhUvHU/kYiHY3uxmPopon6qsQkbURK5lj1f51onXryfpPP/DfOLh3ZrH6v9pYV5nvG7AUycbMPjKFuIT0KIZRwPo3BU8hRMw5i41RBLajIpzIAVSwB29GkzxPCzVaDj6B0cvwnWqr3VXdmlnvbDNgiCnxkSgZ69XZRKVViJC9X/oxEzmvvFuAJL4Bn0o9wJ8BCH/SVlDzERHVhVMyaaDLx1hXo9JP16suALh+j4XVBuuKvDmLP52IiSZmiznyROHlLco33VZZDirS14E9tN0jP4rnWq1euKmEHT8AYBpUnROTFYdvjRmHie2Ob6ITgMpOWgBVPCzvqyY76qLZiMvzCxpGsKN1EbyWsLhjgQNeW 4MPXiw0K BFDOF6XIFJ64yHYPQTOJQcjtB/dcSUei1DywDJKKesWO/dcgzdPyGyfuQMEIc/3bz5XLIumUCckOaHj4uXShsbVaxHIQ65X0bYCGwRrxNkMhAe50g5+YqX80U4nBzdbTdn8cVEiB1x0GTMrOjGRveUC9+k9t12WgWs6tA3UTEO8E7eGJDlRhp44koT4d4Q3AL+8O5Yxtjf1uArquH+PrUiRLq2XaIIT4eM6FWGz7bqxDR8A0YRMR582ZthYaCpwi1Te/uvyNqaYvstZyl13QbsgfJRsGUOEQxbQOYIR4XiXDXmH8HBgD4EEnH+FzihJP+h+QcRWI43hW9NhgSvbdil5tX2cRrkWAhCmRw5pDuCUIGNdEWrC/jwEX0Jxae5bZDncPWPMEKlrV5XtUEhse4EmWiwoQF2Gcw0NPc4Ux/gZ5UbUE= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2024-10-07 15:47, Boqun Feng wrote: > On Thu, Oct 03, 2024 at 09:30:53AM -0400, Mathieu Desnoyers wrote: > [...] >>>> + /* >>>> + * Use RCU dereference without lockdep checks, because >>>> + * lockdep is not aware of HP guarantees. >>>> + */ >>>> + addr2 = rcu_access_pointer(*addr_p); /* Load A */ >>> >>> Why rcu_access_pointer() instead of READ_ONCE()? Because you want to >>> mark the head of address dependency? >> >> Yes, the intent here is to mark the address dependency and provide >> a publication guarantee similar to RCU pairing rcu_assign_pointer >> and rcu_dereference. Do you see any reason why READ_ONCE() would >> suffice here ? > > READ_ONCE() also provides address dependencies. See the "DEPENDENCY > RELATIONS: data, addr, and ctrl" section in > tools/memory-model/Documentation/explanantion.txt. Fair point, so let's use READ_ONCE() then. Thanks, Mathieu > > Regards, > Boqun > >> >> Thanks, >> >> Mathieu >> -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com