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=-8.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 80E65C433DF for ; Wed, 20 May 2020 15:47:30 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 48FDF20709 for ; Wed, 20 May 2020 15:47:30 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="qpRQTKce" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 48FDF20709 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-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=5MJ0OjTZq87PcgaOllykG1wsB1NZ969WqzpA8RuKlL0=; b=qpRQTKce8476at 61ssguwjh3xqABepgTRgdbBuQWRFQT9SuzvZXnW/Et1kEBhUg+YP0Wv8IIJ2EmEd1ZnjzZSVQmUEl OXl4EDwUIGre+MR4VlUcN+2lXI78xe+KNyS+9I6GvVzqDh3PWstfnVuy1fohJ3YDd4PyWiBmmff5E Mokn18TiEHLfQdmxPWAqqgwFJjdAoMOK+pqsaGcGlKrlvNXzB5HZuKHQVr/nJonP3RbpgKHtNx86i HWO6PV8HeH/fuyQO2SAC8SB8vyGNU64H/VIU8ZXhvwA6ZugD21MxraNva3X5NuzS9aAsySZqR2pk4 8c1Cn22SV6t3wju8bVaw==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jbQwC-00066R-CB; Wed, 20 May 2020 15:47:20 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jbQw9-00063o-Mq for linux-arm-kernel@lists.infradead.org; Wed, 20 May 2020 15:47:19 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 421E3D6E; Wed, 20 May 2020 08:47:16 -0700 (PDT) Received: from gaia (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3D5103F305; Wed, 20 May 2020 08:47:14 -0700 (PDT) Date: Wed, 20 May 2020 16:47:11 +0100 From: Catalin Marinas To: Will Deacon Subject: Re: [PATCH] arm64/cpufeature: Move BUG_ON() inside get_arm64_ftr_reg() Message-ID: <20200520154711.GD18302@gaia> References: <1589937774-20479-1-git-send-email-anshuman.khandual@arm.com> <20200520122012.GA25815@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200520122012.GA25815@willie-the-truck> 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-20200520_084717_788499_724DA1AE X-CRM114-Status: GOOD ( 22.57 ) 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: mark.rutland@arm.com, Suzuki K Poulose , Anshuman Khandual , linux-kernel@vger.kernel.org, Mark Brown , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, May 20, 2020 at 01:20:13PM +0100, Will Deacon wrote: > On Wed, May 20, 2020 at 06:52:54AM +0530, Anshuman Khandual wrote: > > There is no way to proceed when requested register could not be searched in > > arm64_ftr_reg[]. Requesting for a non present register would be an error as > > well. Hence lets just BUG_ON() when the search fails in get_arm64_ftr_reg() > > rather than checking for return value and doing the same in some individual > > callers. > > > > But there are some callers that dont BUG_ON() upon search failure. It adds > > an argument 'failsafe' that provides required switch between callers based > > on whether they could proceed or not. > > > > Cc: Catalin Marinas > > Cc: Will Deacon > > Cc: Suzuki K Poulose > > Cc: Mark Brown > > Cc: linux-arm-kernel@lists.infradead.org > > Cc: linux-kernel@vger.kernel.org > > > > Signed-off-by: Anshuman Khandual > > --- > > Applies on next-20200518 that has recent cpufeature changes from Will. > > > > arch/arm64/kernel/cpufeature.c | 26 +++++++++++++------------- > > 1 file changed, 13 insertions(+), 13 deletions(-) > > > > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > > index bc5048f152c1..62767cc540c3 100644 > > --- a/arch/arm64/kernel/cpufeature.c > > +++ b/arch/arm64/kernel/cpufeature.c > > @@ -557,7 +557,7 @@ static int search_cmp_ftr_reg(const void *id, const void *regp) > > * - NULL on failure. It is upto the caller to decide > > * the impact of a failure. > > */ > > -static struct arm64_ftr_reg *get_arm64_ftr_reg(u32 sys_id) > > +static struct arm64_ftr_reg *get_arm64_ftr_reg(u32 sys_id, bool failsafe) > > Generally, I'm not a big fan of boolean arguments because they are really > opaque at the callsite. It also seems bogus to me that we don't trust the > caller to pass a valid sys_id, but we trust it to get "failsafe" right, > which seems to mean "I promise to check the result isn't NULL before > dereferencing it." > > So I don't see how this patch improves anything. I'd actually be more > inclined to stick a WARN() in get_arm64_ftr_reg() when it returns NULL and > have the callers handle NULL by returning early, getting rid of all the > BUG_ONs in here. Sure, the system might end up in a funny state, but we > WARN()d about it and tried to keep going (and Linus has some strong opinions > on this too). Such WARN can be triggered by the user via emulate_sys_reg(), so we can't really have it in get_arm64_ftr_reg() without a 'failsafe' option. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel