From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 858F6C433E2 for ; Wed, 2 Sep 2020 14:11:01 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 453DF2078E for ; Wed, 2 Sep 2020 14:11:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 453DF2078E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id D733C6B0080; Wed, 2 Sep 2020 10:11:00 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D25116B0081; Wed, 2 Sep 2020 10:11:00 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C3BA36B0082; Wed, 2 Sep 2020 10:11:00 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0143.hostedemail.com [216.40.44.143]) by kanga.kvack.org (Postfix) with ESMTP id AEA786B0080 for ; Wed, 2 Sep 2020 10:11:00 -0400 (EDT) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 775C48248047 for ; Wed, 2 Sep 2020 14:11:00 +0000 (UTC) X-FDA: 77218307880.21.mind44_480b9b9270a1 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin21.hostedemail.com (Postfix) with ESMTP id 31E6D180442C4 for ; Wed, 2 Sep 2020 14:11:00 +0000 (UTC) X-HE-Tag: mind44_480b9b9270a1 X-Filterd-Recvd-Size: 3964 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf05.hostedemail.com (Postfix) with ESMTP for ; Wed, 2 Sep 2020 14:10:59 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 91439B64A; Wed, 2 Sep 2020 14:10:59 +0000 (UTC) Date: Wed, 2 Sep 2020 16:10:57 +0200 From: Michal Hocko To: Pavel Tatashin Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org, Vlastimil Babka , Mel Gorman Subject: Re: [PATCH] mm/memory_hotplug: drain per-cpu pages again during memory offline Message-ID: <20200902141057.GK4617@dhcp22.suse.cz> References: <20200901124615.137200-1-pasha.tatashin@soleen.com> <20200902140116.GI4617@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200902140116.GI4617@dhcp22.suse.cz> X-Rspamd-Queue-Id: 31E6D180442C4 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed 02-09-20 16:01:17, Michal Hocko wrote: > [Cc Mel and Vlastimil - I am still rummaging] > > On Tue 01-09-20 08:46:15, Pavel Tatashin wrote: > > There is a race during page offline that can lead to infinite loop: > > a page never ends up on a buddy list and __offline_pages() keeps > > retrying infinitely or until a termination signal is received. > > > > Thread#1 - a new process: > > > > load_elf_binary > > begin_new_exec > > exec_mmap > > mmput > > exit_mmap > > tlb_finish_mmu > > tlb_flush_mmu > > release_pages > > free_unref_page_list > > free_unref_page_prepare > > set_pcppage_migratetype(page, migratetype); > > // Set page->index migration type below MIGRATE_PCPTYPES > > > > Thread#2 - hot-removes memory > > __offline_pages > > start_isolate_page_range > > set_migratetype_isolate > > set_pageblock_migratetype(page, MIGRATE_ISOLATE); > > Set migration type to MIGRATE_ISOLATE-> set > > drain_all_pages(zone); > > // drain per-cpu page lists to buddy allocator. > > > > Thread#1 - continue > > free_unref_page_commit > > migratetype = get_pcppage_migratetype(page); > > // get old migration type > > list_add(&page->lru, &pcp->lists[migratetype]); > > // add new page to already drained pcp list > > > > Thread#2 > > Never drains pcp again, and therefore gets stuck in the loop. > > > > The fix is to try to drain per-cpu lists again after > > check_pages_isolated_cb() fails. Still trying to wrap my head around this but I think this is not a proper fix. It should be the page isolation to make sure no races are possible with the page freeing path. > > Signed-off-by: Pavel Tatashin > > Cc: stable@vger.kernel.org > > --- > > mm/memory_hotplug.c | 9 +++++++++ > > 1 file changed, 9 insertions(+) > > > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > > index e9d5ab5d3ca0..d6d54922bfce 100644 > > --- a/mm/memory_hotplug.c > > +++ b/mm/memory_hotplug.c > > @@ -1575,6 +1575,15 @@ static int __ref __offline_pages(unsigned long start_pfn, > > /* check again */ > > ret = walk_system_ram_range(start_pfn, end_pfn - start_pfn, > > NULL, check_pages_isolated_cb); > > + /* > > + * per-cpu pages are drained in start_isolate_page_range, but if > > + * there are still pages that are not free, make sure that we > > + * drain again, because when we isolated range we might > > + * have raced with another thread that was adding pages to > > + * pcp list. > > + */ > > + if (ret) > > + drain_all_pages(zone); > > } while (ret); > > > > /* Ok, all of our target is isolated. > > -- > > 2.25.1 > > > > -- > Michal Hocko > SUSE Labs -- Michal Hocko SUSE Labs