From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752635AbaLAD4d (ORCPT ); Sun, 30 Nov 2014 22:56:33 -0500 Received: from mail-pa0-f54.google.com ([209.85.220.54]:46508 "EHLO mail-pa0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752536AbaLAD4c (ORCPT ); Sun, 30 Nov 2014 22:56:32 -0500 Date: Sun, 30 Nov 2014 19:56:29 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Andrew Morton cc: Kelley Nielsen , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH] mm: fix swapoff hang after page migration and fork Message-ID: User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I've been seeing swapoff hangs in recent testing: it's cycling around trying unsuccessfully to find an mm for some remaining pages of swap. I have been exercising swap and page migration more heavily recently, and now notice a long-standing error in copy_one_pte(): it's trying to add dst_mm to swapoff's mmlist when it finds a swap entry, but is doing so even when it's a migration entry or an hwpoison entry. Which wouldn't matter much, except it adds dst_mm next to src_mm, assuming src_mm is already on the mmlist: which may not be so. Then if pages are later swapped out from dst_mm, swapoff won't be able to find where to replace them. There's already a !non_swap_entry() test for stats: move that up before the swap_duplicate() and the addition to mmlist. Signed-off-by: Hugh Dickins Cc: stable@vger.kernel.org # 2.6.18+ --- mm/memory.c | 24 ++++++++++++------------ 1 file changed, 12 insertions(+), 12 deletions(-) --- 3.18-rc7/mm/memory.c 2014-11-02 20:21:39.929011061 -0800 +++ linux/mm/memory.c 2014-11-27 19:38:52.314801502 -0800 @@ -815,20 +815,20 @@ copy_one_pte(struct mm_struct *dst_mm, s if (!pte_file(pte)) { swp_entry_t entry = pte_to_swp_entry(pte); - if (swap_duplicate(entry) < 0) - return entry.val; + if (likely(!non_swap_entry(entry))) { + if (swap_duplicate(entry) < 0) + return entry.val; - /* make sure dst_mm is on swapoff's mmlist. */ - if (unlikely(list_empty(&dst_mm->mmlist))) { - spin_lock(&mmlist_lock); - if (list_empty(&dst_mm->mmlist)) - list_add(&dst_mm->mmlist, - &src_mm->mmlist); - spin_unlock(&mmlist_lock); - } - if (likely(!non_swap_entry(entry))) + /* make sure dst_mm is on swapoff's mmlist. */ + if (unlikely(list_empty(&dst_mm->mmlist))) { + spin_lock(&mmlist_lock); + if (list_empty(&dst_mm->mmlist)) + list_add(&dst_mm->mmlist, + &src_mm->mmlist); + spin_unlock(&mmlist_lock); + } rss[MM_SWAPENTS]++; - else if (is_migration_entry(entry)) { + } else if (is_migration_entry(entry)) { page = migration_entry_to_page(entry); if (PageAnon(page))