From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756164AbcJGFqG (ORCPT ); Fri, 7 Oct 2016 01:46:06 -0400 Received: from LGEAMRELO11.lge.com ([156.147.23.51]:38084 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752748AbcJGFpk (ORCPT ); Fri, 7 Oct 2016 01:45:40 -0400 X-Original-SENDERIP: 156.147.1.126 X-Original-MAILFROM: minchan@kernel.org X-Original-SENDERIP: 10.177.223.161 X-Original-MAILFROM: minchan@kernel.org From: Minchan Kim To: Andrew Morton Cc: Mel Gorman , Vlastimil Babka , Joonsoo Kim , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Sangseok Lee , Minchan Kim Subject: [PATCH 2/4] mm: prevent double decrease of nr_reserved_highatomic Date: Fri, 7 Oct 2016 14:45:34 +0900 Message-Id: <1475819136-24358-3-git-send-email-minchan@kernel.org> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1475819136-24358-1-git-send-email-minchan@kernel.org> References: <1475819136-24358-1-git-send-email-minchan@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org There is race between page freeing and unreserved highatomic. CPU 0 CPU 1 free_hot_cold_page mt = get_pfnblock_migratetype set_pcppage_migratetype(page, mt) unreserve_highatomic_pageblock spin_lock_irqsave(&zone->lock) move_freepages_block set_pageblock_migratetype(page) spin_unlock_irqrestore(&zone->lock) free_pcppages_bulk __free_one_page(mt) <- mt is stale By above race, a page on CPU 0 could go non-highorderatomic free list since the pageblock's type is changed. By that, unreserve logic of highorderatomic can decrease reserved count on a same pageblock several times and then it will make mismatch between nr_reserved_highatomic and the number of reserved pageblock. So, this patch verifies whether the pageblock is highatomic or not and decrease the count only if the pageblock is highatomic. Signed-off-by: Minchan Kim --- mm/page_alloc.c | 24 ++++++++++++++++++------ 1 file changed, 18 insertions(+), 6 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index e7cbb3cc22fa..d110cd640264 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2133,13 +2133,25 @@ static void unreserve_highatomic_pageblock(const struct alloc_context *ac) continue; /* - * It should never happen but changes to locking could - * inadvertently allow a per-cpu drain to add pages - * to MIGRATE_HIGHATOMIC while unreserving so be safe - * and watch for underflows. + * In page freeing path, migratetype change is racy so + * we can counter several free pages in a pageblock + * in this loop althoug we changed the pageblock type + * from highatomic to ac->migratetype. So we should + * adjust the count once. */ - zone->nr_reserved_highatomic -= min(pageblock_nr_pages, - zone->nr_reserved_highatomic); + if (get_pageblock_migratetype(page) == + MIGRATE_HIGHATOMIC) { + /* + * It should never happen but changes to + * locking could inadvertently allow a per-cpu + * drain to add pages to MIGRATE_HIGHATOMIC + * while unreserving so be safe and watch for + * underflows. + */ + zone->nr_reserved_highatomic -= min( + pageblock_nr_pages, + zone->nr_reserved_highatomic); + } /* * Convert to ac->migratetype and avoid the normal -- 2.7.4