From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx148.postini.com [74.125.245.148]) by kanga.kvack.org (Postfix) with SMTP id 73C476B005C for ; Wed, 13 Jun 2012 21:12:15 -0400 (EDT) From: Minchan Kim Subject: [PATCH v2 1/2][BUGFIX] mm: do not use page_count without a page pin Date: Thu, 14 Jun 2012 10:12:13 +0900 Message-Id: <1339636334-9238-1-git-send-email-minchan@kernel.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Minchan Kim , Andrea Arcangeli , Mel Gorman , Michal Hocko , KAMEZAWA Hiroyuki , Wanpeng Li d179e84ba fixed the problem[1] in vmscan.c but same problem is here. Let's fix it. [1] http://comments.gmane.org/gmane.linux.kernel.mm/65844 I copy and paste d179e84ba's contents for description. "It is unsafe to run page_count during the physical pfn scan because compound_head could trip on a dangling pointer when reading page->first_page if the compound page is being freed by another CPU." * changelog from v1 - Add comment about skip tail page of THP - Andrea - fix typo - Wanpeng Li - based on next-20120613 Cc: Andrea Arcangeli Cc: Mel Gorman Cc: Michal Hocko Cc: KAMEZAWA Hiroyuki Cc: Wanpeng Li Signed-off-by: Minchan Kim --- mm/page_alloc.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 266f267..543cc2d 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5496,11 +5496,18 @@ __count_immobile_pages(struct zone *zone, struct page *page, int count) continue; page = pfn_to_page(check); - if (!page_count(page)) { + /* + * We can't use page_count without pin a page + * because another CPU can free compound page. + * This check already skips compound tails of THP + * because their page->_count is zero at all time. + */ + if (!atomic_read(&page->_count)) { if (PageBuddy(page)) iter += (1 << page_order(page)) - 1; continue; } + if (!PageLRU(page)) found++; /* -- 1.7.9.5 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org