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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 D0BBAC4363D for ; Fri, 25 Sep 2020 12:35:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9842821D91 for ; Fri, 25 Sep 2020 12:35:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728453AbgIYMfK (ORCPT ); Fri, 25 Sep 2020 08:35:10 -0400 Received: from mail.kernel.org ([198.145.29.99]:44816 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728056AbgIYMfK (ORCPT ); Fri, 25 Sep 2020 08:35:10 -0400 Received: from gaia (unknown [31.124.44.166]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 02FF021D7A; Fri, 25 Sep 2020 12:35:06 +0000 (UTC) Date: Fri, 25 Sep 2020 13:35:04 +0100 From: Catalin Marinas To: Andrey Konovalov Cc: Dmitry Vyukov , Vincenzo Frascino , kasan-dev , Andrey Ryabinin , Alexander Potapenko , Marco Elver , Evgenii Stepanov , Elena Petrova , Branislav Rankov , Kevin Brodsky , Will Deacon , Andrew Morton , Linux ARM , Linux Memory Management List , LKML Subject: Re: [PATCH v3 26/39] arm64: mte: Add in-kernel tag fault handler Message-ID: <20200925123503.GJ4846@gaia> References: <17ec8af55dc0a4d3ade679feb0858f0df4c80d27.1600987622.git.andreyknvl@google.com> <20200925104933.GD4846@gaia> <20200925114703.GI4846@gaia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 25, 2020 at 01:52:56PM +0200, Andrey Konovalov wrote: > On Fri, Sep 25, 2020 at 1:47 PM Catalin Marinas wrote: > > On Fri, Sep 25, 2020 at 01:26:02PM +0200, Andrey Konovalov wrote: > > > On Fri, Sep 25, 2020 at 12:49 PM Catalin Marinas > > > wrote: > > > > > + > > > > > static void __do_kernel_fault(unsigned long addr, unsigned int esr, > > > > > struct pt_regs *regs) > > > > > { > > > > > @@ -641,10 +647,40 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs) > > > > > return 0; > > > > > } > > > > > > > > > > +static void do_tag_recovery(unsigned long addr, unsigned int esr, > > > > > + struct pt_regs *regs) > > > > > +{ > > > > > + static bool reported = false; > > > > > + > > > > > + if (!READ_ONCE(reported)) { > > > > > + report_tag_fault(addr, esr, regs); > > > > > + WRITE_ONCE(reported, true); > > > > > + } > > > > > > > > I don't mind the READ_ONCE/WRITE_ONCE here but not sure what they help > > > > with. > > > > > > The fault can happen on multiple cores at the same time, right? In > > > that case without READ/WRITE_ONCE() we'll have a data-race here. > > > > READ/WRITE_ONCE won't magically solve such races. If two CPUs enter > > simultaneously in do_tag_recovery(), they'd both read 'reported' as > > false and both print the fault info. > > They won't solve the race condition, but they will solve the data > race. I guess here we don't really care about the race condition, as > printing a tag fault twice is OK. But having a data race here will > lead to KCSAN reports, although won't probably break anything in > practice. I agree, in practice it should be fine. Anyway, it doesn't hurt leaving them in place. -- Catalin