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 <hu...@google.com>
Cc: sta...@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))
--
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