From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752710AbdKMLye (ORCPT ); Mon, 13 Nov 2017 06:54:34 -0500 Received: from mx2.suse.de ([195.135.220.15]:45145 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752408AbdKMLyd (ORCPT ); Mon, 13 Nov 2017 06:54:33 -0500 Date: Mon, 13 Nov 2017 12:54:30 +0100 From: Michal Hocko To: Arnd Bergmann Cc: Stephen Rothwell , Andrew Morton , Linux-Next Mailing List , Linux Kernel Mailing List Subject: Re: linux-next: build warning after merge of the akpm-current tree Message-ID: <20171113115430.pms47vgz5uszqsjm@dhcp22.suse.cz> References: <20171113164206.187a790d@canb.auug.org.au> <20171113080955.zcdzx2p5kzoa4d7s@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 13-11-17 12:43:08, Arnd Bergmann wrote: > On Mon, Nov 13, 2017 at 9:09 AM, Michal Hocko wrote: > > On Mon 13-11-17 16:42:06, Stephen Rothwell wrote: > >> Hi Andrew, > >> > >> After merging the akpm-current tree, today's linux-next build (powerpc > >> ppc64_defconfig) produced this warning: > >> > >> In file included from include/linux/mmzone.h:17:0, > >> from include/linux/mempolicy.h:10, > >> from mm/mempolicy.c:70: > >> mm/mempolicy.c: In function 'mpol_to_str': > >> include/linux/nodemask.h:107:41: warning: the address of 'nodes' will always evaluate as 'true' [-Waddress] > >> #define nodemask_pr_args(maskp) (maskp) ? MAX_NUMNODES : 0, (maskp) ? (maskp)->bits : NULL > >> ^ > >> mm/mempolicy.c:2817:11: note: in expansion of macro 'nodemask_pr_args' > >> nodemask_pr_args(&nodes)); > >> ^ > > > > Hmm, this warning is quite surprising to me. Sure in this particular > > case maskp will always be non-NULL so we always expand to > > MAX_NUMNODES, maskp->bits > > which is what we want. But we have other users which may be NULL. Does > > anybody understan why this warns at all? > > As I understand it, the warning tries to address a common typo of accidentally > testing the pointer to a stack object for being non-NULL, rather than the object > pointed to for being non-zero. > > Adding an extra '!= NULL' comparison gets rid of the warning for me: > > #define nodemask_pr_args(maskp) \ > ((maskp) != NULL) ? MAX_NUMNODES : 0, \ > ((maskp) != NULL) ?(maskp)->bits : NULL OK, that is a reasonable workaround. I was talking to our gcc guy and he suggested to report a bug for this. Andrew, could you fold the explicit != NULL check into the patch please? -- Michal Hocko SUSE Labs