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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham 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 185DDC5CFEB for ; Wed, 11 Jul 2018 10:55:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B23572083C for ; Wed, 11 Jul 2018 10:55:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B23572083C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732509AbeGKK7N (ORCPT ); Wed, 11 Jul 2018 06:59:13 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:33202 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732376AbeGKK7M (ORCPT ); Wed, 11 Jul 2018 06:59:12 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E40DB80D; Wed, 11 Jul 2018 03:55:27 -0700 (PDT) Received: from e103592.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 482303F589; Wed, 11 Jul 2018 03:55:26 -0700 (PDT) Date: Wed, 11 Jul 2018 11:55:23 +0100 From: Dave Martin To: "Yandong.Zhao" Cc: zhaoxb@thundersoft.com, ard.biesheuvel@linaro.org, catalin.marinas@arm.com, will.deacon@arm.com, linux-kernel@vger.kernel.org, zhaoyd@thundersoft.com, linux-arm-kernel@lists.infradead.org, fanlc0801@thundersoft.com Subject: Re: [PATCH] arm64: neon: Fix function may_use_simd() return error status Message-ID: <20180711105523.GL9486@e103592.cambridge.arm.com> References: <1531271399-1768-1-git-send-email-yandong77520@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1531271399-1768-1-git-send-email-yandong77520@gmail.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 11, 2018 at 09:09:59AM +0800, Yandong.Zhao wrote: > From: Yandong Zhao > > It does not matter if the caller of may_use_simd() migrates to > another cpu after the call, but it is still important that the > kernel_neon_busy percpu instance that is read matches the cpu the > task is running on at the time of the read. > > This means that raw_cpu_read() is not sufficient. kernel_neon_busy > may appear true if the caller migrates during the execution of > raw_cpu_read() and the next task to be scheduled in on the initial > cpu calls kernel_neon_begin(). > > This patch replaces raw_cpu_read() with this_cpu_read() to protect > against this race. > > Signed-off-by: Yandong Zhao Looks ok to me. You can add the following tags: Fixes: cb84d11e1625 ("arm64: neon: Remove support for nested or hardirq kernel-mode NEON") Reviewed-by: Dave Martin Cheers ---Dave > --- > arch/arm64/include/asm/simd.h | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/include/asm/simd.h b/arch/arm64/include/asm/simd.h > index fa8b3fe..784a8c2 100644 > --- a/arch/arm64/include/asm/simd.h > +++ b/arch/arm64/include/asm/simd.h > @@ -29,7 +29,8 @@ > static __must_check inline bool may_use_simd(void) > { > /* > - * The raw_cpu_read() is racy if called with preemption enabled. > + * The this_cpu_read() is racy if called with preemption enabled, > + * since the task may subsequently migrate to another CPU. > * This is not a bug: kernel_neon_busy is only set when > * preemption is disabled, so we cannot migrate to another CPU > * while it is set, nor can we migrate to a CPU where it is set. > @@ -42,7 +43,7 @@ static __must_check inline bool may_use_simd(void) > * false. > */ > return !in_irq() && !irqs_disabled() && !in_nmi() && > - !raw_cpu_read(kernel_neon_busy); > + !this_cpu_read(kernel_neon_busy); > } > > #else /* ! CONFIG_KERNEL_MODE_NEON */ > -- > 1.9.1 > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel