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 A4322C433E2 for ; Wed, 2 Sep 2020 14:09:08 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 6D1FD207D3 for ; Wed, 2 Sep 2020 14:09:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6D1FD207D3 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 F26F36B0055; Wed, 2 Sep 2020 10:09:07 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id ED70C6B006C; Wed, 2 Sep 2020 10:09:07 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DEC626B0080; Wed, 2 Sep 2020 10:09:07 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0174.hostedemail.com [216.40.44.174]) by kanga.kvack.org (Postfix) with ESMTP id C536C6B0055 for ; Wed, 2 Sep 2020 10:09:07 -0400 (EDT) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 7DC52180ACF75 for ; Wed, 2 Sep 2020 14:09:07 +0000 (UTC) X-FDA: 77218303134.21.name91_4f0207a270a1 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin21.hostedemail.com (Postfix) with ESMTP id DAC02180442CE for ; Wed, 2 Sep 2020 14:08:53 +0000 (UTC) X-HE-Tag: name91_4f0207a270a1 X-Filterd-Recvd-Size: 3683 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf30.hostedemail.com (Postfix) with ESMTP for ; Wed, 2 Sep 2020 14:08:53 +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 4ECA7AEFA; Wed, 2 Sep 2020 14:08:53 +0000 (UTC) Date: Wed, 2 Sep 2020 16:08:51 +0200 From: Michal Hocko To: Pavel Tatashin Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org Subject: Re: [PATCH] mm/memory_hotplug: drain per-cpu pages again during memory offline Message-ID: <20200902140851.GJ4617@dhcp22.suse.cz> References: <20200901124615.137200-1-pasha.tatashin@soleen.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200901124615.137200-1-pasha.tatashin@soleen.com> X-Rspamd-Queue-Id: DAC02180442CE X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 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 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. It is not really clear to me how we could have passed has_unmovable_pages at this stage when the page is not PageBuddy. Is this because you are using Movable Zones? > > 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. But this means that the page is not isolated and so it could be reused for something else. No? > 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