[PATCH 5/5] mm/migrate.c: fix potential deadlock in NUMA balancing shared exec THP case

Miaohe Lin
2021-03-20T09:38:08Z

Since commit c77c5cbafe54 ("mm: migrate: skip shared exec THP for NUMA
balancing"), the NUMA balancing would skip shared exec transhuge page.
But this enhancement is not suitable for transhuge page. Because it's
required that page_mapcount() must be 1 due to no migration pte dance
is done here. On the other hand, the shared exec transhuge page will
leave the migrate_misplaced_page() with pte entry untouched and page
locked. Thus pagefault for NUMA will be triggered again and deadlock
occurs when we start waiting for the page lock held by ourselves.

Fixes: c77c5cbafe54 ("mm: migrate: skip shared exec THP for NUMA balancing")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
mm/migrate.c | 4 ----
1 file changed, 4 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 3e169b72d7b2..67a941c52b6d 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2192,9 +2192,6 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
int page_lru = page_is_file_lru(page);
unsigned long start = address & HPAGE_PMD_MASK;

- if (is_shared_exec_page(vma, page))
- goto out;
-
new_page = alloc_pages_node(node,
(GFP_TRANSHUGE_LIGHT | __GFP_THISNODE),
HPAGE_PMD_ORDER);
@@ -2306,7 +2303,6 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,

out_unlock:
unlock_page(page);
-out:
put_page(page);
return 0;
}
--
2.19.1