From 2022b4d18a491a578218ce7a4eca8666db895a73 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Tue, 2 Dec 2014 15:59:39 -0800 Subject: [PATCH] mm: fix swapoff hang after page migration and fork 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: Kelley Nielsen Cc: [2.6.18+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/memory.c | 26 +++++++++++++------------- 1 file changed, 13 insertions(+), 13 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index 3e503831e042..d5f2ae9c4a23 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -815,20 +815,20 @@ copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm, if (!pte_file(pte)) { swp_entry_t entry = pte_to_swp_entry(pte); - 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))) + 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); + } rss[MM_SWAPENTS]++; - else if (is_migration_entry(entry)) { + } else if (is_migration_entry(entry)) { page = migration_entry_to_page(entry); if (PageAnon(page)) -- 2.20.1