From: Zi Yan <ziy@xxxxxxxxxx>
The tail pages in a THP can have swap entry information stored in their
private field. When migrating to a new page, all tail pages of the new
page need to update ->private to avoid future data corruption.
This fix is stable-only, since after commit 07e09c483cbe ("mm/huge_memory:
work on folio->swap instead of page->private when splitting folio"),
subpages of a swapcached THP no longer requires the maintenance.
Adding THPs to the swapcache was introduced in commit
38d8b4e6bdc87 ("mm, THP, swap: delay splitting THP during swap out"),
where each subpage of a THP added to the swapcache had its own swapcache
entry and required the ->private field to point to the correct swapcache
entry. Later, when THP migration functionality was implemented in commit
616b8371539a6 ("mm: thp: enable thp migration in generic path"),
it initially did not handle the subpages of swapcached THPs, failing to
update their ->private fields or replace the subpage pointers in the
swapcache. Subsequently, commit e71769ae5260 ("mm: enable thp migration
for shmem thp") addressed the swapcache update aspect. This patch fixes
the update of subpage ->private fields.
Closes: https://lore.kernel.org/linux-mm/1707814102-22682-1-git-send-email-quic_charante@xxxxxxxxxxx/
Fixes: 616b8371539a ("mm: thp: enable thp migration in generic path")
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
---
mm/migrate.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/mm/migrate.c b/mm/migrate.c
index 034b0662fd3b..9cfd53eaeb4e 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -441,8 +441,12 @@ int migrate_page_move_mapping(struct address_space *mapping,
if (PageSwapBacked(page)) {
__SetPageSwapBacked(newpage);
if (PageSwapCache(page)) {
+ int i;
+
SetPageSwapCache(newpage);
- set_page_private(newpage, page_private(page));
+ for (i = 0; i < (1 << compound_order(page)); i++)
+ set_page_private(newpage + i,
+ page_private(page + i));
}
} else {
VM_BUG_ON_PAGE(PageSwapCache(page), page);
--
2.43.0
