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Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kLmwS-00013D-Mt; Fri, 25 Sep 2020 12:35:12 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kLmwQ-00012b-B2 for linux-arm-kernel@lists.infradead.org; Fri, 25 Sep 2020 12:35:11 +0000 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 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-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200925_083510_447889_C156AED6 X-CRM114-Status: GOOD ( 22.49 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Linux ARM , Marco Elver , Elena Petrova , Kevin Brodsky , Will Deacon , Branislav Rankov , kasan-dev , LKML , Linux Memory Management List , Alexander Potapenko , Evgenii Stepanov , Andrey Ryabinin , Andrew Morton , Vincenzo Frascino , Dmitry Vyukov Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel