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 95A9DCCFA07 for ; Thu, 26 Sep 2024 06:16:54 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id BC1236B0093; Thu, 26 Sep 2024 02:16:53 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B716A6B0098; Thu, 26 Sep 2024 02:16:53 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9C2426B0099; Thu, 26 Sep 2024 02:16:53 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 752006B0093 for ; Thu, 26 Sep 2024 02:16:53 -0400 (EDT) Received: from smtpin21.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 18F7B81398 for ; Thu, 26 Sep 2024 06:16:53 +0000 (UTC) X-FDA: 82605881106.21.65BAD2D Received: from smtpout.efficios.com (smtpout.efficios.com [167.114.26.122]) by imf29.hostedemail.com (Postfix) with ESMTP id 3A2BF12000F for ; Thu, 26 Sep 2024 06:16:51 +0000 (UTC) Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=efficios.com header.s=smtpout1 header.b=uaTffgAN; dmarc=pass (policy=none) header.from=efficios.com; spf=pass (imf29.hostedemail.com: domain of mathieu.desnoyers@efficios.com designates 167.114.26.122 as permitted sender) smtp.mailfrom=mathieu.desnoyers@efficios.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1727331322; a=rsa-sha256; cv=none; b=OWFWS6E55dGvKHqeAzhWDom1wFPwY/qM0m/Oey6ArJOxACgnkpB9W7HHWOGeLprrQEZgag MrI2mCnWsUGzh52Nt4JzaYtX/K3SkrRrERGMq6WFL1+MPhgJ8R/IC29epVVL5zxXw/LRqr rnRT0culAPpsEcW58Gp6b55E/xMpuJg= ARC-Authentication-Results: i=1; imf29.hostedemail.com; dkim=pass header.d=efficios.com header.s=smtpout1 header.b=uaTffgAN; dmarc=pass (policy=none) header.from=efficios.com; spf=pass (imf29.hostedemail.com: domain of mathieu.desnoyers@efficios.com designates 167.114.26.122 as permitted sender) smtp.mailfrom=mathieu.desnoyers@efficios.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1727331322; 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=sSaPuqnnGyFhl1X4Is48q78ldLnHXKOz5esXPHTnDRI=; b=BC6flK+J/L9GiS3SBZXzSp2Nly4Tks2Ys39FNLqI1aPEmp27xm0S28u6LGJTPpYMg3ogya eGaWnpHHT6pilsRC9wNBR8Kn3cZPg20Q3wWctXLy+QeMclkcmAnWIcrY85Th8dJkFQlyVe h6cOS2eEZq9UUIQe1EOe9lpWNYdrc0M= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=efficios.com; s=smtpout1; t=1727331410; bh=2MryQ9y2u2yCeiP4+Tmgt60Q1T0o9VzZCCgVPAQ/SZU=; h=Date:Subject:From:To:Cc:References:In-Reply-To:From; b=uaTffgANpcaUG2l8vb0K1oMGlBXjCqou0aHpmIM+BLQrVN0IZp2fMg7Ssvr+ZRW3R XUsN8xAiiO2th9NYdxyix6uCqOlSPM5iCEheI1dGDlT6uC6gPe+DD33cXoJxKidxMK z75GOFKd2AEr4AHEf/516Z/+Acb1iEKhyEKZjwTx9O9WIje0J02IexJFYPA/bPu11/ joB/V6tVu5lfcC4w89rfGmD3CWDkkGEIIa6fSreoibsZVGe/JPFeSNiQeBw9RqSDwD vEMWG0p4v4n0sg15c9W6UkNh//E9gmUpFgVWjE8L+t76+j6YGT2bOquVMAx3P5eO73 6e92FeOV8q31Q== Received: from [172.17.2.162] (unknown [178.208.16.192]) by smtpout.efficios.com (Postfix) with ESMTPSA id 4XDjzg1sCtz1M6s; Thu, 26 Sep 2024 02:16:47 -0400 (EDT) Message-ID: <2b2aea37-06fe-40cb-8458-9408406ebda6@efficios.com> Date: Thu, 26 Sep 2024 08:16:08 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 1/4] hazptr: Add initial implementation of hazard pointers From: Mathieu Desnoyers To: Boqun Feng Cc: Jonas Oberhauser , linux-kernel@vger.kernel.org, rcu@vger.kernel.org, linux-mm@kvack.org, lkmm@lists.linux.dev, "Paul E. McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Uladzislau Rezki , Steven Rostedt , Lai Jiangshan , Zqiang , Peter Zijlstra , Ingo Molnar , Will Deacon , Waiman Long , Mark Rutland , Thomas Gleixner , Kent Overstreet , Linus Torvalds , Vlastimil Babka , maged.michael@gmail.com, Neeraj Upadhyay References: <20240917143402.930114-1-boqun.feng@gmail.com> <20240917143402.930114-2-boqun.feng@gmail.com> <55975a55-302f-4c45-bfcc-192a8a1242e9@huaweicloud.com> <4167e6f5-4ff9-4aaa-915e-c1e692ac785a@efficios.com> <48992c9f-6c61-4716-977c-66e946adb399@efficios.com> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 3A2BF12000F X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 15gu3joj4e163ym9hhsks7qwm3iz84u6 X-HE-Tag: 1727331411-717085 X-HE-Meta: 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 vF3b7+RV cby52NkosMTrtpe/fc6FMoHEUrlpnPHeIkUOC5l9eZbRjH/5y5Xr4QrhLLnhTh8DhOjEOy8TJC1u4Q2NBNGYkXpima1GQT40tGBz0nQWBeDIBVghG+rHA6Uve8MzJn8Izv0Gq+yFU9fvoQHw2KtD/KIiNgo1Ji8jTZ4tCPU5FmYJl9nUgEyhJUXhcC9wInSbABv96FH1iQZaknk/NE2kBhJWlVABiH8B+Xfr+MBGfx1rKoUm0xoM/dLQV4oy4DXtcm9YH59EzhcNB2y4apbSDmIDJC5FNcyG868XVvWTFUlw40xyF/0HqZSjW8aUVevyyEAVYwqLEUIJcKfpMG+qPomI7NfsbkM3mJInRyIuE9g/lBCG743jT0TJBGgM76xmwi4JlEiFh8A3qNw7GZXCnl0PPo8R/OdBin6BEgigeDu+L/JHP6PIe5McMZKatmRfco8PcQcelUoXz314= 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 2024-09-25 15:20, Mathieu Desnoyers wrote: [...] > static inline > bool same_ptr(void *a, void *b) > { >     asm goto ( >         "cmpq %[a], %[b]\n\t" >         "jne %l[ne]\n\t" >         : : [a] "r" (a), [b] "r" (b) >         : : ne); >     return true; > ne: >     return false; > } Based on the information provided in this email thread, it appears the only concern when it comes to comparing a pointer loaded by rcu_dereference() with another pointer is the possibility of compiler optimizations. In the specific case of hazard pointer hpref_hp_get(), this function does both loads which are then compared with one another. Therefore, it is not possible for the user to provide a comparison value known at compile-time, except in the unlikely scenario where the hazard pointer would be const, which does not really make much sense. Therefore, just using rcu_dereference() for the second load should be fine. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com