From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752718AbdFVHvJ (ORCPT ); Thu, 22 Jun 2017 03:51:09 -0400 Received: from mail-wr0-f169.google.com ([209.85.128.169]:33531 "EHLO mail-wr0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751177AbdFVHvH (ORCPT ); Thu, 22 Jun 2017 03:51:07 -0400 Date: Thu, 22 Jun 2017 09:51:04 +0200 From: Ingo Molnar To: Arnd Bergmann Cc: "Paul E. McKenney" , Thomas Gleixner , Sebastian Andrzej Siewior , Anna-Maria Gleixner , Boris Ostrovsky , Linux Kernel Mailing List Subject: Re: [PATCH] rcu: remove unused variable in boot_cpu_state_init Message-ID: <20170622075104.dlajhtcx7p3sgacs@gmail.com> References: <20170621215741.4028236-1-arnd@arndb.de> <20170621221054.GU3721@linux.vnet.ibm.com> <20170622072644.so23jacjhvrox5pd@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Arnd Bergmann wrote: > > So I think we should consider it a syntactic construct to avoid. > > Unused variables are relatively harmless compared to used-uninitialized > variables that are always bugs (though they are provably impossible to > detect correctly in some cases). So the thing I was most worried about was that old GCC used to not warn about: long __maybe_unused error; ... if (error) return error; ... but recent GCC does warn if it's certain that the use is uninitialized, so the scenario I outlined should not happen. But it will supress the warning if the variable is uninitialized but GCC cannot prove it for sure, so my point remains that it's a potentially dangerous construct. Thanks, Ingo