From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx133.postini.com [74.125.245.133]) by kanga.kvack.org (Postfix) with SMTP id 884A36B0034 for ; Mon, 12 Aug 2013 11:43:30 -0400 (EDT) Received: by mail-qa0-f46.google.com with SMTP id bq6so1096093qab.12 for ; Mon, 12 Aug 2013 08:43:29 -0700 (PDT) From: j.glisse@gmail.com Subject: [PATCH] mm: fix special swap entry handling on copy mm Date: Mon, 12 Aug 2013 11:43:24 -0400 Message-Id: <1376322204-20659-1-git-send-email-j.glisse@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Jerome Glisse From: Jerome Glisse Prior to this copy_one_pte will never reach the special swap file handling code because swap_duplicate will return invalid value. Note this is not fatal so nothing bad ever happen because of that. Reason is that copy_pte_range would break of its loop and call add_swap_count_continuation which would see its a special swap file and return 0 triggering copy_pte_range to try again. Because we try again there is a huge chance that the temporarily special migration pte is now again valid and pointing to a new valid page. This patch just split handling of special swap entry from regular one inside copy_one_pte. (Note i spotted that while reading code i haven't tested my theory.) Signed-off-by: Jerome Glisse --- mm/memory.c | 26 +++++++++++++------------- 1 file changed, 13 insertions(+), 13 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index 1ce2e2a..9f907dd 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -833,20 +833,20 @@ 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)) -- 1.8.3.1 -- 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