From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: 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 <hughd@xxxxxxxxxx>
Cc: Kelley Nielsen <kelleynnn@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [2.6.18+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memory.c | 24 ++++++++++++------------
1 file changed, 12 insertions(+), 12 deletions(-)
diff -puN mm/memory.c~mm-fix-swapoff-hang-after-page-migration-and-fork mm/memory.c
--- a/mm/memory.c~mm-fix-swapoff-hang-after-page-migration-and-fork
+++ a/mm/memory.c
@@ -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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