From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753284AbdLNOGM (ORCPT ); Thu, 14 Dec 2017 09:06:12 -0500 Received: from mx2.suse.de ([195.135.220.15]:43975 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752659AbdLNOGK (ORCPT ); Thu, 14 Dec 2017 09:06:10 -0500 Date: Thu, 14 Dec 2017 15:06:08 +0100 From: Michal Hocko To: Andrew Morton Cc: JianKang Chen , mgorman@techsingularity.net, hannes@cmpxchg.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, xieyisheng1@huawei.com, guohanjun@huawei.com, wangkefeng.wang@huawei.com Subject: Re: [PATCH resend] mm/page_alloc: fix comment is __get_free_pages Message-ID: <20171214140608.GQ16951@dhcp22.suse.cz> References: <1511780964-64864-1-git-send-email-chenjiankang1@huawei.com> <20171127113341.ldx32qvexqe2224d@dhcp22.suse.cz> <20171129160446.jluzpv3n6mjc3fwv@dhcp22.suse.cz> <20171129134159.c9100ea6dacad870d69929b7@linux-foundation.org> <20171130065335.zno7peunnl2zpozq@dhcp22.suse.cz> <20171130131706.0550cd28ce47aaa976f7db2a@linux-foundation.org> <20171201072414.3kc3pbvdbqbxhnfx@dhcp22.suse.cz> <20171201111845.iyoua7hhjodpuvoy@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171201111845.iyoua7hhjodpuvoy@dhcp22.suse.cz> User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 01-12-17 12:18:45, Michal Hocko wrote: > On Fri 01-12-17 08:24:14, Michal Hocko wrote: > > On Thu 30-11-17 13:17:06, Andrew Morton wrote: > > > On Thu, 30 Nov 2017 07:53:35 +0100 Michal Hocko wrote: > > > > > > > > mm... So we have a caller which hopes to be getting highmem pages but > > > > > isn't. Caller then proceeds to pointlessly kmap the page and wonders > > > > > why it isn't getting as much memory as it would like on 32-bit systems, > > > > > etc. > > > > > > > > How he can kmap the page when he gets a _virtual_ address? > > > > > > doh. > > > > > > > > I do think we should help ferret out such bogosity. A WARN_ON_ONCE > > > > > would suffice. > > > > > > > > This function has always been about lowmem pages. I seriously doubt we > > > > have anybody confused and asking for a highmem page in the kernel. I > > > > haven't checked that but it would already blow up as VM_BUG_ON tends to > > > > be enabled on many setups. > > > > > > OK. But silently accepting __GFP_HIGHMEM is a bit weird - callers > > > shouldn't be doing that in the first place. > > > > Yes, they shouldn't be. > > > > > I wonder what happens if we just remove the WARN_ON and pass any > > > __GFP_HIGHMEM straight through. The caller gets a weird address from > > > page_to_virt(highmem page) and usually goes splat? Good enough > > > treatment for something which never happens anyway? > > > > page_address will return NULL so they will blow up and leak the freshly > > allocated memory. > > let me be more specific. They will blow up and leak if the returned > address is not checked. If it is then we just leak. None of that sounds > good to me. So do we care and I will resend the patch in that case or I just drop this from my patch queue? -- Michal Hocko SUSE Labs