Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932343AbaJWIOx (ORCPT ); Thu, 23 Oct 2014 04:14:53 -0400 Received: from lgeamrelo02.lge.com ([156.147.1.126]:34150 "EHLO lgeamrelo02.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753410AbaJWIJX (ORCPT ); Thu, 23 Oct 2014 04:09:23 -0400 X-Original-SENDERIP: 10.177.222.213 X-Original-MAILFROM: iamjoonsoo.kim@lge.com From: Joonsoo Kim To: Andrew Morton Cc: "Kirill A. Shutemov" , Rik van Riel , Peter Zijlstra , Mel Gorman , Johannes Weiner , Minchan Kim , Yasuaki Ishimatsu , Zhang Yanfei , Tang Chen , Naoya Horiguchi , Bartlomiej Zolnierkiewicz , Wen Congyang , Marek Szyprowski , Michal Nazarewicz , Laura Abbott , Heesub Shin , "Aneesh Kumar K.V" , Ritesh Harjani , t.stanislaws@samsung.com, Gioh Kim , Vlastimil Babka , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Joonsoo Kim , Subject: [PATCH v4 1/4] mm/page_alloc: fix incorrect isolation behavior by rechecking migratetype Date: Thu, 23 Oct 2014 17:10:18 +0900 Message-Id: <1414051821-12769-2-git-send-email-iamjoonsoo.kim@lge.com> X-Mailer: git-send-email 1.7.9.5 In-Reply-To: <1414051821-12769-1-git-send-email-iamjoonsoo.kim@lge.com> References: <1414051821-12769-1-git-send-email-iamjoonsoo.kim@lge.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org There are two paths to reach core free function of buddy allocator, __free_one_page(), one is free_one_page()->__free_one_page() and the other is free_hot_cold_page()->free_pcppages_bulk()->__free_one_page(). Each paths has race condition causing serious problems. At first, this patch is focused on first type of freepath. And then, following patch will solve the problem in second type of freepath. In the first type of freepath, we got migratetype of freeing page without holding the zone lock, so it could be racy. There are two cases of this race. 1. pages are added to isolate buddy list after restoring orignal migratetype CPU1 CPU2 get migratetype => return MIGRATE_ISOLATE call free_one_page() with MIGRATE_ISOLATE grab the zone lock unisolate pageblock release the zone lock grab the zone lock call __free_one_page() with MIGRATE_ISOLATE freepage go into isolate buddy list, although pageblock is already unisolated This may cause two problems. One is that we can't use this page anymore until next isolation attempt of this pageblock, because freepage is on isolate buddy list. The other is that freepage accouting could be wrong due to merging between different buddy list. Freepages on isolate buddy list aren't counted as freepage, but ones on normal buddy list are counted as freepage. If merge happens, buddy freepage on normal buddy list is inevitably moved to isolate buddy list without any consideration of freepage accouting so it could be incorrect. 2. pages are added to normal buddy list while pageblock is isolated. It is similar with above case. This also may cause two problems. One is that we can't keep these freepages from being allocated. Although this pageblock is isolated, freepage would be added to normal buddy list so that it could be allocated without any restriction. And the other problem is same as case 1, that it, incorrect freepage accouting. This race condition would be prevented by checking migratetype again with holding the zone lock. Because it is somewhat heavy operation and it isn't needed in common case, we want to avoid rechecking as much as possible. So this patch introduce new variable, nr_isolate_pageblock in struct zone to check if there is isolated pageblock. With this, we can avoid to re-check migratetype in common case and do it only if there is isolated pageblock or migratetype is MIGRATE_ISOLATE. This solve above mentioned problems. Changes from v3: Add one more check in free_one_page() that checks whether migratetype is MIGRATE_ISOLATE or not. Without this, abovementioned case 1 could happens. Cc: Signed-off-by: Joonsoo Kim --- include/linux/mmzone.h | 9 +++++++++ include/linux/page-isolation.h | 8 ++++++++ mm/page_alloc.c | 11 +++++++++-- mm/page_isolation.c | 2 ++ 4 files changed, 28 insertions(+), 2 deletions(-) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 4593567..3d090af 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -431,6 +431,15 @@ struct zone { */ int nr_migrate_reserve_block; +#ifdef CONFIG_MEMORY_ISOLATION + /* + * Number of isolated pageblock. It is used to solve incorrect + * freepage counting problem due to racy retrieving migratetype + * of pageblock. Protected by zone->lock. + */ + unsigned long nr_isolate_pageblock; +#endif + #ifdef CONFIG_MEMORY_HOTPLUG /* see spanned/present_pages for more description */ seqlock_t span_seqlock; diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h index 3fff8e7..2dc1e16 100644 --- a/include/linux/page-isolation.h +++ b/include/linux/page-isolation.h @@ -2,6 +2,10 @@ #define __LINUX_PAGEISOLATION_H #ifdef CONFIG_MEMORY_ISOLATION +static inline bool has_isolate_pageblock(struct zone *zone) +{ + return zone->nr_isolate_pageblock; +} static inline bool is_migrate_isolate_page(struct page *page) { return get_pageblock_migratetype(page) == MIGRATE_ISOLATE; @@ -11,6 +15,10 @@ static inline bool is_migrate_isolate(int migratetype) return migratetype == MIGRATE_ISOLATE; } #else +static inline bool has_isolate_pageblock(struct zone *zone) +{ + return false; +} static inline bool is_migrate_isolate_page(struct page *page) { return false; diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 70027da..4a5d8e5 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -749,9 +749,16 @@ static void free_one_page(struct zone *zone, if (nr_scanned) __mod_zone_page_state(zone, NR_PAGES_SCANNED, -nr_scanned); + if (unlikely(has_isolate_pageblock(zone) || + is_migrate_isolate(migratetype))) { + migratetype = get_pfnblock_migratetype(page, pfn); + if (is_migrate_isolate(migratetype)) + goto skip_counting; + } + __mod_zone_freepage_state(zone, 1 << order, migratetype); + +skip_counting: __free_one_page(page, pfn, zone, order, migratetype); - if (unlikely(!is_migrate_isolate(migratetype))) - __mod_zone_freepage_state(zone, 1 << order, migratetype); spin_unlock(&zone->lock); } diff --git a/mm/page_isolation.c b/mm/page_isolation.c index d1473b2..1fa4a4d 100644 --- a/mm/page_isolation.c +++ b/mm/page_isolation.c @@ -60,6 +60,7 @@ out: int migratetype = get_pageblock_migratetype(page); set_pageblock_migratetype(page, MIGRATE_ISOLATE); + zone->nr_isolate_pageblock++; nr_pages = move_freepages_block(zone, page, MIGRATE_ISOLATE); __mod_zone_freepage_state(zone, -nr_pages, migratetype); @@ -83,6 +84,7 @@ void unset_migratetype_isolate(struct page *page, unsigned migratetype) nr_pages = move_freepages_block(zone, page, migratetype); __mod_zone_freepage_state(zone, nr_pages, migratetype); set_pageblock_migratetype(page, migratetype); + zone->nr_isolate_pageblock--; out: spin_unlock_irqrestore(&zone->lock, flags); } -- 1.7.9.5 -- 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/