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Wed, 1 Apr 2020 23:00:29 +0000 Date: Wed, 1 Apr 2020 20:00:24 -0300 From: Jason Gunthorpe To: Andrew Morton Cc: Stephen Rothwell , Linux Next Mailing List , Linux Kernel Mailing List , Longpeng , Mike Kravetz , Matthew Wilcox , Sean Christopherson Subject: Re: linux-next: build warning after merge of the akpm-current tree Message-ID: <20200401230024.GY8514@mellanox.com> References: <20200331195612.64c06485@canb.auug.org.au> <20200401155831.24aa79ebbb14c654a2bee8c0@linux-foundation.org> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200401155831.24aa79ebbb14c654a2bee8c0@linux-foundation.org> User-Agent: Mutt/1.9.4 (2018-02-28) X-ClientProxiedBy: MN2PR05CA0051.namprd05.prod.outlook.com (2603:10b6:208:236::20) To VI1PR05MB4141.eurprd05.prod.outlook.com (2603:10a6:803:44::15) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from mlx.ziepe.ca (142.68.57.212) by MN2PR05CA0051.namprd05.prod.outlook.com (2603:10b6:208:236::20) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.2900.5 via Frontend Transport; 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X-Microsoft-Antispam-Message-Info: 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 X-MS-Exchange-AntiSpam-MessageData: yk3e688ht29iUKtczYCYpOVj605rZLaxffFszuEdCIoRfshzyYuJezwfT9RhjmPzzHZP/80aQ2FLPXmSDza+MFFphgEvU2Ut3/5GOKoNbrvnUa/f0NYJ8GTWxKQobqjsw//SJfiHkymgzrw4bEQ5Ow== X-OriginatorOrg: Mellanox.com X-MS-Exchange-CrossTenant-Network-Message-Id: 782fed45-2782-4d65-3288-08d7d69078cf X-MS-Exchange-CrossTenant-OriginalArrivalTime: 01 Apr 2020 23:00:29.1251 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: a652971c-7d2e-4d9b-a6a4-d149256f461b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: nf3TFOmMaaIMMMa4XdayT/D2fqqPzARzps8R6yZkJK2ZmZOXUmpAETyuGa9bb7nt0e1773B52EWMGKY7gPfQKQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: VI1PR05MB6845 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 01, 2020 at 03:58:31PM -0700, Andrew Morton wrote: > On Tue, 31 Mar 2020 19:56:12 +1100 Stephen Rothwell wrote: > > > Hi all, > > > > After merging the akpm-current tree, today's linux-next build (i386 > > defconfig) produced this warning: > > > > mm/hugetlb.c: In function 'huge_pte_offset': > > cc1: warning: function may return address of local variable [-Wreturn-local-addr] > > mm/hugetlb.c:5361:14: note: declared here > > 5361 | pud_t *pud, pud_entry; > > | ^~~~~~~~~ > > cc1: warning: function may return address of local variable [-Wreturn-local-addr] > > mm/hugetlb.c:5360:14: note: declared here > > 5360 | p4d_t *p4d, p4d_entry; > > | ^~~~~~~~~ > > > > Introduced by commit > > > > 826ddc88e2cf ("mm/hugetlb: fix a addressing exception caused by huge_pte_offset") > > I can reproduce this (i386 defconfig, gcc-7.2.0). > > I can see no way in which this makes any sense. Hopefully it's a gcc > bug but it's hard to see how it could have messed up this fairly simple > code. It is a code bug, there was a little thread about this. It happens because the address of a stack variable is passed into the pXX_offset functions which return that address when the page levels are folded. I recommend to drop this patch until it is adjusted.. Jason