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=-2.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,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 EE384C3A5A2 for ; Tue, 10 Sep 2019 13:24:30 +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 B367C2084D for ; Tue, 10 Sep 2019 13:24:30 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="Ekb5alhr"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="QXJGMdSY" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B367C2084D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org 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=C3NY0PIvKeOjJsDeTMzVh4Pw8jwnAcu+w3qKSCujnKs=; b=Ekb5alhrb4VQcW YGN6R5ESXIzPMP+naYHGy7x9qCWSsY18vfj0O6VlkTbbeaZpuWRMr66eUudWqf+fwJGGH/vEAFL8h jIWmZevlg7e8uXELt+lKvGD3NanO6iA74/RUFapaFgfvgcDZqLwdoYv1rz/oZv+6mVFeWn0hYv7RM oXsh5QXyqJf1Mjv5k2b51jluEqdvX0siVmu2AfUMg0foRmlL5W1A5rX9t1v+z8/RzeY9pCEoYDYxj KQLtiJiMpYgOuJ+iRV7kDe+aMPnBTYWhDFO4Ep1n3NQQ5l5PsZhxphxmoP2ACUV/DyAzbYwrGVsfR 5XpSfLK987yrAImCU5wA==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1i7g88-0006nB-TE; Tue, 10 Sep 2019 13:24:24 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1i7g86-0006mX-0R for linux-arm-kernel@lists.infradead.org; Tue, 10 Sep 2019 13:24:23 +0000 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (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 2A11F2067B; Tue, 10 Sep 2019 13:24:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1568121861; bh=pnVHhUoA0bQkP4vAFyAiTnaV2vHizoN7pMNixvUz4Xo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=QXJGMdSYwg11CHswIYBqj4ts9Z2dVSTLWmih/qgJkikZh0AkTYGXL36ue2YP1eo/3 WlvCFhAvWd67NqgUkVLu5zZwv/MYLkiz9FQ6f8zpJDob8YMGyJD1W2ZtI1eTJPyN2i 4J8W+Jn7BKTUvXG3S2Lqz+MxeTJ7EK20sA1gd468= Date: Tue, 10 Sep 2019 14:24:15 +0100 From: Will Deacon To: Arnd Bergmann Subject: Re: [PATCH] arm64: fix unreachable code issue with cmpxchg Message-ID: <20190910132415.4j2ygxhuanihvzhx@willie-the-truck> References: <20190909202153.144970-1-arnd@arndb.de> <20190910074606.45k5m2pkztlpj4nj@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190910_062422_093819_F04E5BA6 X-CRM114-Status: GOOD ( 22.52 ) 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 , Masahiro Yamada , Catalin Marinas , "linux-kernel@vger.kernel.org" , clang-built-linux , Ingo Molnar , Andrew Murray , Borislav Petkov , Linux ARM 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 Tue, Sep 10, 2019 at 10:04:24AM +0200, Arnd Bergmann wrote: > On Tue, Sep 10, 2019 at 9:46 AM Will Deacon wrote: > > > > On Mon, Sep 09, 2019 at 10:21:35PM +0200, Arnd Bergmann wrote: > > > On arm64 build with clang, sometimes the __cmpxchg_mb is not inlined > > > when CONFIG_OPTIMIZE_INLINING is set. > > > > Hmm. Given that CONFIG_OPTIMIZE_INLINING has also been shown to break > > assignment of local 'register' variables on GCC, perhaps we should just > > disable that option for arm64 (at least) since we don't have any toolchains > > that seem to like it very much! I'd certainly prefer that over playing > > whack-a-mole with __always_inline. > > Right, but I can also see good reasons to keep going: > > - In theory, CONFIG_OPTIMIZE_INLINING is the right thing to do -- the compilers > also make some particularly bad decisions around inlining when each inline > turns into an __always_inline, as has been the case in Linux for a long time. > I think in most cases, we get better object code with CONFIG_OPTIMIZE_INLINING > and in the cases where this is worse, it may be better to fix the compiler. > The new "asm_inline" macro should also help with that. Sure, in theory, but it looks like there isn't a single arm64 compiler out there which gets it right. > - The x86 folks have apparently whacked most of the moles already, see this > commit from 2008 > > commit 3f9b5cc018566ad9562df0648395649aebdbc5e0 > Author: Ingo Molnar > Date: Fri Jul 18 16:30:05 2008 +0200 > > x86: re-enable OPTIMIZE_INLINING > > re-enable OPTIMIZE_INLINING more widely. Jeff Dike fixed the remaining > outstanding issue in this commit: > > | commit 4f81c5350b44bcc501ab6f8a089b16d064b4d2f6 > | Author: Jeff Dike > | Date: Mon Jul 7 13:36:56 2008 -0400 > | > | [UML] fix gcc ICEs and unresolved externs > [...] > | This patch reintroduces unit-at-a-time for gcc >= 4.0, > bringing back the > | possibility of Uli's crash. If that happens, we'll debug it. > > it's still default-off and thus opt-in. This appears to be fixing an ICE, whereas the issue reported recently for arm64 gcc was silent miscompilation of atomics in some cases. Unfortunately, I can't seem to find the thread :/ Mark, you were on that one too, right? > - The inlining decisions of gcc and clang are already very different, and > the bugs we are finding around that are much more common than > the difference between CONFIG_OPTIMIZE_INLINING=y/n on a > given compiler. Sorry, not sure that you're getting at here. Anyway, the second version of your patch looks fine, but I would still prefer to go the extra mile and disable CONFIG_OPTIMIZE_INLINING altogether given that I don't think it's a safe option to enable for us. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel