From c612edbc5ec6743dbec78f7dc696679e33bdcc22 Mon Sep 17 00:00:00 2001 From: Zi Yan Date: Wed, 6 Mar 2024 10:51:57 -0500 Subject: [PATCH] mm/migrate: set swap entry values of THP tail pages properly. 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@quicinc.com/ Fixes: 616b8371539a ("mm: thp: enable thp migration in generic path") Signed-off-by: Zi Yan Acked-by: David Hildenbrand Signed-off-by: Greg Kroah-Hartman --- mm/migrate.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/mm/migrate.c b/mm/migrate.c index c7d5566623ad..c37af50f312d 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -424,8 +424,12 @@ 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);