Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932282AbbHNIjZ (ORCPT ); Fri, 14 Aug 2015 04:39:25 -0400 Received: from TYO202.gate.nec.co.jp ([210.143.35.52]:62057 "EHLO tyo202.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932094AbbHNIjS convert rfc822-to-8bit (ORCPT ); Fri, 14 Aug 2015 04:39:18 -0400 From: Naoya Horiguchi To: Wanpeng Li CC: Andrew Morton , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] mm/hwpoison: fix race between soft_offline_page and unpoison_memory Thread-Topic: [PATCH] mm/hwpoison: fix race between soft_offline_page and unpoison_memory Thread-Index: AQHQ1Zq57OyJ15BfMkCMbnAvybI4V54JCPoAgAAHGQCAAAyggIAABpQAgAErgoCAAAxcgIAAJ++AgAAHxACAAAFTgIAACuIA Date: Fri, 14 Aug 2015 08:38:18 +0000 Message-ID: <20150814083818.GB6956@hori1.linux.bs1.fc.nec.co.jp> References: <20150813085332.GA30163@hori1.linux.bs1.fc.nec.co.jp> <20150813100407.GA2993@hori1.linux.bs1.fc.nec.co.jp> <20150814041939.GA9951@hori1.linux.bs1.fc.nec.co.jp> <20150814072649.GA31021@hori1.linux.bs1.fc.nec.co.jp>

In-Reply-To: Accept-Language: ja-JP, en-US Content-Language: ja-JP X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.128.101.24] Content-Type: text/plain; charset="iso-2022-jp" Content-ID: Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2345 Lines: 51 On Fri, Aug 14, 2015 at 03:59:21PM +0800, Wanpeng Li wrote: > On 8/14/15 3:54 PM, Wanpeng Li wrote: > >[...] > >>OK, then I rethink of handling the race in unpoison_memory(). > >> > >>Currently properly contained/hwpoisoned pages should have page refcount 1 > >>(when the memory error hits LRU pages or hugetlb pages) or refcount 0 > >>(when the memory error hits the buddy page.) And current unpoison_memory() > >>implicitly assumes this because otherwise the unpoisoned page has no place > >>to go and it's just leaked. > >>So to avoid the kernel panic, adding prechecks of refcount and mapcount > >>to limit the page to unpoison for only unpoisonable pages looks OK to me. > >>The page under soft offlining always has refcount >=2 and/or mapcount > 0, > >>so such pages should be filtered out. > >> > >>Here's a patch. In my testing (run soft offline stress testing then repeat > >>unpoisoning in background,) the reported (or similar) bug doesn't happen. > >>Can I have your comments? > >As page_action() prints out page maybe still referenced by some users, > >however, PageHWPoison has already set. So you will leak many poison pages. > > > > Anyway, the bug is still there. > > [ 944.387559] BUG: Bad page state in process expr pfn:591e3 > [ 944.393053] page:ffffea00016478c0 count:-1 mapcount:0 mapping: > (null) index:0x2 > [ 944.401147] flags: 0x1fffff80000000() > [ 944.404819] page dumped because: nonzero _count Hmm, no luck :( To investigate more, I'd like to test the exactly same kernel as yours, so could you share the kernel info (.config and base kernel and what patches you applied)? or pushing your tree somewhere like github? # if you like, sending to me privately is fine. I think that I tested v4.2-rc6 + + "mm/hwpoison: fix race between soft_offline_page and unpoison_memory", but I experienced some conflict in applying your patches for some reason, so it might happen that we are testing on different kernels. Mine is here: https://github.com/Naoya-Horiguchi/linux v4.2-rc6/fix_race_soft_offline_unpoison Thanks, Naoya Horiguchi-- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/