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=-7.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 623AFC48BE6 for ; Wed, 16 Jun 2021 18:45:48 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 1C4EE613E2 for ; Wed, 16 Jun 2021 18:45:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1C4EE613E2 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 9A7676B0036; Wed, 16 Jun 2021 14:45:47 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 97E756B006C; Wed, 16 Jun 2021 14:45:47 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7F7226B0070; Wed, 16 Jun 2021 14:45:47 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0177.hostedemail.com [216.40.44.177]) by kanga.kvack.org (Postfix) with ESMTP id 4A36B6B0036 for ; Wed, 16 Jun 2021 14:45:47 -0400 (EDT) Received: from smtpin19.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id DDC24801A1D7 for ; Wed, 16 Jun 2021 18:45:46 +0000 (UTC) X-FDA: 78260465892.19.56A2646 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf29.hostedemail.com (Postfix) with ESMTP id 96BA037A for ; Wed, 16 Jun 2021 18:45:32 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 6FF50613EF; Wed, 16 Jun 2021 18:45:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1623869145; bh=cGUCVYHomHwqNgu6aUOX7H52KAGhAXiilh/Q/DUf0fM=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=Nn2kI+GV0anZTeOFWqbRiCO2sMskw9+VzvHl2Ld/a92jKx9LcsBZVS/Ug3ZBy/BBQ KOJvjbD8pMnDelhQRWr0FfkF+XXmNJAubFJhpE+QUlUjG59prJ6oJ5JRVE7dE/4K1p HsBxB6uVHVE/MPh6aZ0d2DSGxPiLe8lf5R2hhxpq7VadUQTDPilKxg2unVn/NI0BlG OQqXVHlspHAvO7QtYecgk43UHoDoFPPxVVem+dk8lQfqB4cGlVt3xXAeJeqv99PcTQ kdUSToNm2S/ISvtwKvUde6ANF2jgYWZkCGFP+PDy+1+8xzRjxmXfGVqms3WOwLEf/N CaeTIh64/frOA== Subject: Re: [PATCH 5/8] membarrier, kthread: Use _ONCE accessors for task->mm To: Mathieu Desnoyers Cc: x86 , Dave Hansen , linux-kernel , linux-mm , Andrew Morton , Nicholas Piggin , Peter Zijlstra References: <74ace142f48db7d0e71b05b5ace72bfe8e0a2652.1623813516.git.luto@kernel.org> <987970694.9105.1623866911729.JavaMail.zimbra@efficios.com> From: Andy Lutomirski Message-ID: <7e411333-2fbc-6254-671f-bf2cba486bcd@kernel.org> Date: Wed, 16 Jun 2021 11:45:44 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <987970694.9105.1623866911729.JavaMail.zimbra@efficios.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 96BA037A Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=Nn2kI+GV; spf=pass (imf29.hostedemail.com: domain of luto@kernel.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=luto@kernel.org; dmarc=pass (policy=none) header.from=kernel.org X-Stat-Signature: kqjzrbh7mez6w5nkq3y8mhety4jascda X-HE-Tag: 1623869132-440593 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: On 6/16/21 11:08 AM, Mathieu Desnoyers wrote: > ----- On Jun 15, 2021, at 11:21 PM, Andy Lutomirski luto@kernel.org wrote: > >> membarrier reads cpu_rq(remote cpu)->curr->mm without locking. Use >> READ_ONCE() and WRITE_ONCE() to remove the data races. > > I notice that kernel/exit.c:exit_mm() also has: > > current->mm = NULL; > > I suspect you may want to add a WRITE_ONCE() there as well ? Good catch. I was thinking that exit_mm() couldn't execute concurrently with membarrier(), but that's wrong. --Andy