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=-5.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,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 4E043C10F12 for ; Wed, 17 Apr 2019 09:01:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 16BC9217D4 for ; Wed, 17 Apr 2019 09:01:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1555491667; bh=BEasVom47PMugj24F1KQvqhVPi/jf4xgcIShQ0cct9Q=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=K3keO8LJ37PrHPyK++EYzpjUUDvSTCGQQ69QpQDCbUzXCVxcTvxE/KnDrCkGE/gog YHa2hQ004xfL8YVcrSLHKNj952OBUzppGAOBLFS2QDW/sm58MawsJoNMTZjA+ZHKzh 2IWdMVf4aWHuFkMzG6tzZQw0rgaJ0lL7TpPnQ9k8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731485AbfDQJBF (ORCPT ); Wed, 17 Apr 2019 05:01:05 -0400 Received: from mail.kernel.org ([198.145.29.99]:60132 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726237AbfDQJBF (ORCPT ); Wed, 17 Apr 2019 05:01:05 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (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 31DA621773; Wed, 17 Apr 2019 09:01:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1555491664; bh=BEasVom47PMugj24F1KQvqhVPi/jf4xgcIShQ0cct9Q=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=QspXLNjinfzU9rdPnzoDUmzYu+ZBLtgi1/C5H/RtSr6uCWUIOmCVE46zf6esKcOru 0zfa7igR1qJ/ZdLWMoYZdW7eGE/eNhKGcZjbQoMrhmgurXyOgkd2qwKkx4nnsHYF5M DWd41Wmk5zsEyxsctviG4vKhIAVMd6bposfoTndY= Date: Wed, 17 Apr 2019 11:01:02 +0200 From: Greg Kroah-Hartman To: Nathan Chancellor Cc: Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] arm64: futex: Restore oldval initialization to work around buggy compilers Message-ID: <20190417090102.GA11773@kroah.com> References: <20190417072121.4450-1-natechancellor@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190417072121.4450-1-natechancellor@gmail.com> User-Agent: Mutt/1.11.4 (2019-03-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 17, 2019 at 12:21:21AM -0700, Nathan Chancellor wrote: > Commit 045afc24124d ("arm64: futex: Fix FUTEX_WAKE_OP atomic ops with > non-zero result value") removed oldval's zero initialization in > arch_futex_atomic_op_inuser because it is not necessary. Unfortunately, > Android's arm64 GCC 4.9.4 [1] does not agree: > > ../kernel/futex.c: In function 'do_futex': > ../kernel/futex.c:1658:17: warning: 'oldval' may be used uninitialized > in this function [-Wmaybe-uninitialized] > return oldval == cmparg; > ^ > In file included from ../kernel/futex.c:73:0: > ../arch/arm64/include/asm/futex.h:53:6: note: 'oldval' was declared here > int oldval, ret, tmp; > ^ > > GCC fails to follow that when ret is non-zero, futex_atomic_op_inuser > returns right away, avoiding the uninitialized use that it claims. > Restoring the zero initialization works around this issue. > > [1]: https://android.googlesource.com/platform/prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.9/ > > Cc: stable@vger.kernel.org > Fixes: 045afc24124d ("arm64: futex: Fix FUTEX_WAKE_OP atomic ops with non-zero result value") > Signed-off-by: Nathan Chancellor Reviewed-by: Greg Kroah-Hartman