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=-6.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_NEOMUTT 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 C4669C10F12 for ; Wed, 17 Apr 2019 09:53:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9C9612173C for ; Wed, 17 Apr 2019 09:53:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728373AbfDQJxm (ORCPT ); Wed, 17 Apr 2019 05:53:42 -0400 Received: from foss.arm.com ([217.140.101.70]:42038 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727282AbfDQJxl (ORCPT ); Wed, 17 Apr 2019 05:53:41 -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 4975A374; Wed, 17 Apr 2019 02:53:41 -0700 (PDT) Received: from mbp (usa-sjc-mx-foss1.foss.arm.com [217.140.101.70]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0FACD3F68F; Wed, 17 Apr 2019 02:53:39 -0700 (PDT) Date: Wed, 17 Apr 2019 10:53:37 +0100 From: Catalin Marinas To: Nathan Chancellor Cc: Will Deacon , Greg Kroah-Hartman , 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: <20190417095337.xnbdaki7kolqmchx@mbp> 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: NeoMutt/20170113 (1.7.2) Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@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 Thanks. That compiler version doesn't seem very smart. I'll queue this for -rc6. -- Catalin