From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933844AbcECAoX (ORCPT ); Mon, 2 May 2016 20:44:23 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:32789 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933510AbcECAoN (ORCPT ); Mon, 2 May 2016 20:44:13 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Steve Capper , "Kirill A. Shutemov" , Will Deacon , Catalin Marinas , Michal Hocko , Ingo Molnar , Andrew Morton , Linus Torvalds Subject: [PATCH 4.5 132/200] mm: exclude HugeTLB pages from THP page_mapped() logic Date: Mon, 2 May 2016 17:12:11 -0700 Message-Id: <20160503000558.942109322@linuxfoundation.org> X-Mailer: git-send-email 2.8.2 In-Reply-To: <20160503000554.631204776@linuxfoundation.org> References: <20160503000554.631204776@linuxfoundation.org> User-Agent: quilt/0.64 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.5-stable review patch. If anyone has any objections, please let me know. ------------------ From: Steve Capper commit 66ee95d16a7f1b7b4f1dd74a2d81c6e19dc29a14 upstream. HugeTLB pages cannot be split, so we use the compound_mapcount to track rmaps. Currently page_mapped() will check the compound_mapcount, but will also go through the constituent pages of a THP compound page and query the individual _mapcount's too. Unfortunately, page_mapped() does not distinguish between HugeTLB and THP compound pages and assumes that a compound page always needs to have HPAGE_PMD_NR pages querying. For most cases when dealing with HugeTLB this is just inefficient, but for scenarios where the HugeTLB page size is less than the pmd block size (e.g. when using contiguous bit on ARM) this can lead to crashes. This patch adjusts the page_mapped function such that we skip the unnecessary THP reference checks for HugeTLB pages. Fixes: e1534ae95004 ("mm: differentiate page_mapped() from page_mapcount() for compound pages") Signed-off-by: Steve Capper Acked-by: Kirill A. Shutemov Cc: Will Deacon Cc: Catalin Marinas Cc: Michal Hocko Cc: Ingo Molnar Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- include/linux/mm.h | 2 ++ 1 file changed, 2 insertions(+) --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1010,6 +1010,8 @@ static inline bool page_mapped(struct pa page = compound_head(page); if (atomic_read(compound_mapcount_ptr(page)) >= 0) return true; + if (PageHuge(page)) + return false; for (i = 0; i < hpage_nr_pages(page); i++) { if (atomic_read(&page[i]._mapcount) >= 0) return true;