From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933322AbdKBOBM (ORCPT ); Thu, 2 Nov 2017 10:01:12 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:39033 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932401AbdKBOBL (ORCPT ); Thu, 2 Nov 2017 10:01:11 -0400 Subject: Re: [PATCH v1 1/1] mm: buddy page accessed before initialized To: Michal Hocko Cc: steven.sistare@oracle.com, daniel.m.jordan@oracle.com, akpm@linux-foundation.org, mgorman@techsingularity.net, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20171031155002.21691-1-pasha.tatashin@oracle.com> <20171031155002.21691-2-pasha.tatashin@oracle.com> <20171102133235.2vfmmut6w4of2y3j@dhcp22.suse.cz> <20171102135423.voxnzk2qkvfgu5l3@dhcp22.suse.cz> From: Pavel Tatashin Message-ID: <94ab73c0-cd18-f58f-eebe-d585fde319e4@oracle.com> Date: Thu, 2 Nov 2017 10:00:59 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <20171102135423.voxnzk2qkvfgu5l3@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Source-IP: userv0021.oracle.com [156.151.31.71] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/02/2017 09:54 AM, Michal Hocko wrote: > On Thu 02-11-17 09:39:58, Pavel Tatashin wrote: > [...] >> Hi Michal, >> >> Previously as before my project? That is because memory for all struct pages >> was always zeroed in memblock, and in __free_one_page() page_is_buddy() was >> always returning false, thus we never tried to incorrectly remove it from >> the list: >> >> 837 list_del(&buddy->lru); >> >> Now, that memory is not zeroed, page_is_buddy() can return true after kexec >> when memory is dirty (unfortunately memset(1) with CONFIG_VM_DEBUG does not >> catch this case). And proceed further to incorrectly remove buddy from the >> list. > > OK, I thought this was a regression from one of the recent patches. So > the problem is not new. Why don't we see the same problem during the > standard boot? Because, I believe, BIOS is zeroing all the memory for us. > >> This is why we must initialize the computed buddy page beforehand. > > Ble, this is really ugly. I will think about it more. > Another approach that I considered is to split loop inside deferred_init_range() into two loops: one where we initialize pages by calling __init_single_page(), another where we free them to buddy allocator by calling deferred_free_range(). Pasha