From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752536AbdCBPHo (ORCPT ); Thu, 2 Mar 2017 10:07:44 -0500 Received: from mga02.intel.com ([134.134.136.20]:10550 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751518AbdCBPHi (ORCPT ); Thu, 2 Mar 2017 10:07:38 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.35,231,1484035200"; d="scan'208";a="55016382" From: "Kirill A. Shutemov" To: Andrea Arcangeli , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A. Shutemov" , "[4.5+]" Subject: [PATCH] thp: fix another corner case of munlock() vs. THPs Date: Thu, 2 Mar 2017 18:02:52 +0300 Message-Id: <20170302150252.34120-1-kirill.shutemov@linux.intel.com> X-Mailer: git-send-email 2.11.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following test case triggers BUG() in munlock_vma_pages_range(): int main(int argc, char *argv[]) { int fd; system("mount -t tmpfs -o huge=always none /mnt"); fd = open("/mnt/test", O_CREAT | O_RDWR); ftruncate(fd, 4UL << 20); mmap(NULL, 4UL << 20, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_FIXED | MAP_LOCKED, fd, 0); mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_LOCKED, fd, 0); munlockall(); return 0; } The second mmap() create PTE-mapping of the first huge page in file. It makes kernel munlock the page as we never keep PTE-mapped page mlocked. On munlockall() when we handle vma created by the first mmap(), munlock_vma_page() returns page_mask == 0, as the page is not mlocked anymore. On next iteration follow_page_mask() return tail page, but page_mask is HPAGE_NR_PAGES - 1. It makes us skip to the first tail page of the next huge page and step on VM_BUG_ON_PAGE(PageMlocked(page)). The fix is not use the page_mask from follow_page_mask() at all. It has no use for us. Signed-off-by: Kirill A. Shutemov Cc: [4.5+] --- mm/mlock.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/mm/mlock.c b/mm/mlock.c index cdbed8aaa426..665ab75b5533 100644 --- a/mm/mlock.c +++ b/mm/mlock.c @@ -441,7 +441,7 @@ void munlock_vma_pages_range(struct vm_area_struct *vma, while (start < end) { struct page *page; - unsigned int page_mask; + unsigned int page_mask = 0; unsigned long page_increm; struct pagevec pvec; struct zone *zone; @@ -455,8 +455,7 @@ void munlock_vma_pages_range(struct vm_area_struct *vma, * suits munlock very well (and if somehow an abnormal page * has sneaked into the range, we won't oops here: great). */ - page = follow_page_mask(vma, start, FOLL_GET | FOLL_DUMP, - &page_mask); + page = follow_page(vma, start, FOLL_GET | FOLL_DUMP); if (page && !IS_ERR(page)) { if (PageTransTail(page)) { @@ -467,8 +466,8 @@ void munlock_vma_pages_range(struct vm_area_struct *vma, /* * Any THP page found by follow_page_mask() may * have gotten split before reaching - * munlock_vma_page(), so we need to recompute - * the page_mask here. + * munlock_vma_page(), so we need to compute + * the page_mask here instead. */ page_mask = munlock_vma_page(page); unlock_page(page); -- 2.11.0