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=-7.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no 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 CA59AC433E2 for ; Fri, 4 Sep 2020 07:54:55 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 803E120748 for ; Fri, 4 Sep 2020 07:54:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 803E120748 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 1F66C6B0037; 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Fri, 4 Sep 2020 07:54:53 +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 B9F3FAD03; Fri, 4 Sep 2020 07:54:53 +0000 (UTC) Date: Fri, 4 Sep 2020 09:54:52 +0200 From: Michal Hocko To: akpm@linux-foundation.org Cc: mm-commits@vger.kernel.org, vbabka@suse.cz, stable@vger.kernel.org, rientjes@google.com, richard.weiyang@gmail.com, osalvador@suse.de, david@redhat.com, pasha.tatashin@soleen.com, linux-mm@kvack.org Subject: Re: + mm-memory_hotplug-drain-per-cpu-pages-again-during-memory-offline.patch added to -mm tree Message-ID: <20200904075452.GE15277@dhcp22.suse.cz> References: <20200903192901.PWYfu%akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200903192901.PWYfu%akpm@linux-foundation.org> X-Rspamd-Queue-Id: 7D3401814B0C1 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 Thu 03-09-20 12:29:01, Andrew Morton wrote: > From: Pavel Tatashin > Subject: mm/memory_hotplug: drain per-cpu pages again during memory offline > > 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. > > Link: https://lkml.kernel.org/r/20200903140032.380431-1-pasha.tatashin@soleen.com > Fixes: c52e75935f8d ("mm: remove extra drain pages on pcp list") > Signed-off-by: Pavel Tatashin > Acked-by: David Rientjes > Acked-by: Vlastimil Babka > Cc: Michal Hocko > Cc: Oscar Salvador > Cc: Wei Yang > Cc: David Hildenbrand > Cc: > Signed-off-by: Andrew Morton Acked-by: Michal Hocko > --- > > mm/memory_hotplug.c | 14 ++++++++++++++ > mm/page_isolation.c | 8 ++++++++ > 2 files changed, 22 insertions(+) > > --- a/mm/memory_hotplug.c~mm-memory_hotplug-drain-per-cpu-pages-again-during-memory-offline > +++ a/mm/memory_hotplug.c > @@ -1575,6 +1575,20 @@ static int __ref __offline_pages(unsigne > /* 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. > --- a/mm/page_isolation.c~mm-memory_hotplug-drain-per-cpu-pages-again-during-memory-offline > +++ a/mm/page_isolation.c > @@ -170,6 +170,14 @@ __first_valid_page(unsigned long pfn, un > * 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. > */ > _ > > Patches currently in -mm which might be from pasha.tatashin@soleen.com are > > mm-memory_hotplug-drain-per-cpu-pages-again-during-memory-offline.patch -- Michal Hocko SUSE Labs