Messages in this thread Patch in this message | | | From | j.glisse@gmail ... | Subject | [PATCH] mm: fix special swap entry handling on copy mm | Date | Mon, 12 Aug 2013 11:43:24 -0400 |
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From: Jerome Glisse <jglisse@redhat.com>
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 <jglisse@redhat.com> --- 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
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