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=-9.8 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 6C12EC43461 for ; Mon, 7 Sep 2020 07:27:04 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 0378B2075A for ; Mon, 7 Sep 2020 07:27:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0378B2075A 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 5FEEF6B0003; Mon, 7 Sep 2020 03:27:03 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5AEEB6B0037; Mon, 7 Sep 2020 03:27:03 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4EC806B0055; Mon, 7 Sep 2020 03:27:03 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0184.hostedemail.com [216.40.44.184]) by kanga.kvack.org (Postfix) with ESMTP id 3A1636B0003 for ; Mon, 7 Sep 2020 03:27:03 -0400 (EDT) Received: from smtpin16.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id E640B181AC9CB for ; Mon, 7 Sep 2020 07:27:02 +0000 (UTC) X-FDA: 77235433884.16.basin49_550497a270ca Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin16.hostedemail.com (Postfix) with ESMTP id B5D5B100E690C for ; Mon, 7 Sep 2020 07:27:02 +0000 (UTC) X-HE-Tag: basin49_550497a270ca X-Filterd-Recvd-Size: 5201 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf09.hostedemail.com (Postfix) with ESMTP for ; Mon, 7 Sep 2020 07:27:02 +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 C9F43ACF2; Mon, 7 Sep 2020 07:27:01 +0000 (UTC) Date: Mon, 7 Sep 2020 09:27:00 +0200 From: Michal Hocko To: Pavel Tatashin Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org, osalvador@suse.de, richard.weiyang@gmail.com, david@redhat.com, vbabka@suse.cz, rientjes@google.com Subject: Re: [PATCH v3 1/2] mm/memory_hotplug: drain per-cpu pages again during memory offline Message-ID: <20200907072700.GF30144@dhcp22.suse.cz> References: <20200904151448.100489-1-pasha.tatashin@soleen.com> <20200904151448.100489-2-pasha.tatashin@soleen.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200904151448.100489-2-pasha.tatashin@soleen.com> X-Rspamd-Queue-Id: B5D5B100E690C 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 Fri 04-09-20 11:14:47, 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. > > Fixes: c52e75935f8d ("mm: remove extra drain pages on pcp list") > > Signed-off-by: Pavel Tatashin > Cc: stable@vger.kernel.org > Acked-by: David Rientjes > Acked-by: Vlastimil Babka Already acked the mmotm version but let's add it here as well. Acked-by: Michal Hocko > --- > mm/memory_hotplug.c | 14 ++++++++++++++ > mm/page_isolation.c | 8 ++++++++ > 2 files changed, 22 insertions(+) > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index e9d5ab5d3ca0..b11a269e2356 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -1575,6 +1575,20 @@ 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. > + * > + * Forward progress should be still guaranteed because > + * pages on the pcp list can only belong to MOVABLE_ZONE > + * because has_unmovable_pages explicitly checks for > + * PageBuddy on freed pages on other zones. > + */ > + if (ret) > + drain_all_pages(zone); > } while (ret); > > /* Ok, all of our target is isolated. > diff --git a/mm/page_isolation.c b/mm/page_isolation.c > index 242c03121d73..63a3db10a8c0 100644 > --- a/mm/page_isolation.c > +++ b/mm/page_isolation.c > @@ -170,6 +170,14 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages) > * pageblocks we may have modified and return -EBUSY to caller. This > * prevents two threads from simultaneously working on overlapping ranges. > * > + * Please note that there is no strong synchronization with the page allocator > + * either. Pages might be freed while their page blocks are marked ISOLATED. > + * In some cases pages might still end up on pcp lists and that would allow > + * for their allocation even when they are in fact isolated already. Depending > + * on how strong of a guarantee the caller needs drain_all_pages might be needed > + * (e.g. __offline_pages will need to call it after check for isolated range for > + * a next retry). > + * > * Return: the number of isolated pageblocks on success and -EBUSY if any part > * of range cannot be isolated. > */ > -- > 2.25.1 > -- Michal Hocko SUSE Labs