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Wed, 16 Jun 2021 14:08:31 -0400 (EDT) Received: from mail03.efficios.com (mail03.efficios.com [167.114.26.124]) by mail.efficios.com (Postfix) with ESMTP id CB6B634A8D5; Wed, 16 Jun 2021 14:08:31 -0400 (EDT) Date: Wed, 16 Jun 2021 14:08:31 -0400 (EDT) From: Mathieu Desnoyers To: Andy Lutomirski Cc: x86 , Dave Hansen , linux-kernel , linux-mm , Andrew Morton , Nicholas Piggin , Peter Zijlstra Message-ID: <987970694.9105.1623866911729.JavaMail.zimbra@efficios.com> In-Reply-To: <74ace142f48db7d0e71b05b5ace72bfe8e0a2652.1623813516.git.luto@kernel.org> References: <74ace142f48db7d0e71b05b5ace72bfe8e0a2652.1623813516.git.luto@kernel.org> Subject: Re: [PATCH 5/8] membarrier, kthread: Use _ONCE accessors for task->mm MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.26.124] X-Mailer: Zimbra 8.8.15_GA_4018 (ZimbraWebClient - FF89 (Linux)/8.8.15_GA_4026) Thread-Topic: membarrier, kthread: Use _ONCE accessors for task->mm Thread-Index: jSWeuglZnPsonKah7Uz3PhyqbxusGQ== Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=efficios.com header.s=default header.b=h3aaimjb; spf=pass (imf23.hostedemail.com: domain of compudj@efficios.com designates 167.114.26.124 as permitted sender) smtp.mailfrom=compudj@efficios.com; dmarc=pass (policy=none) header.from=efficios.com X-Stat-Signature: czp7n13wpy4agy6nqxwtt4h6azfobagg X-Rspamd-Queue-Id: 9C0F7A000248 X-Rspamd-Server: rspam06 X-HE-Tag: 1623866906-495434 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 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 ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com