From a3477c9e02cc9d62a7c8bfc4e7453f5af9a175aa Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Sun, 10 Nov 2024 13:11:21 -0800 Subject: [PATCH] mm/thp: fix deferred split queue not partially_mapped: fix Though even more elusive than before, list_del corruption has still been seen on THP's deferred split queue. The idea in commit e66f3185fa04 was right, but its implementation wrong. The context omitted an important comment just before the critical test: "split_folio() removes folio from list on success." In ignoring that comment, when a THP split succeeded, the code went on to release the preceding safe folio, preserving instead an irrelevant (formerly head) folio: which gives no safety because it's not on the list. Fix the logic. Link: https://lkml.kernel.org/r/3c995a30-31ce-0998-1b9f-3a2cb9354c91@google.com Fixes: e66f3185fa04 ("mm/thp: fix deferred split queue not partially_mapped") Signed-off-by: Hugh Dickins Acked-by: Usama Arif Reviewed-by: Zi Yan Cc: Baolin Wang Cc: Barry Song Cc: Chris Li Cc: David Hildenbrand Cc: Johannes Weiner Cc: Kefeng Wang Cc: Kirill A. Shutemov Cc: Matthew Wilcox Cc: Nhat Pham Cc: Ryan Roberts Cc: Shakeel Butt Cc: Wei Yang Cc: Yang Shi Signed-off-by: Andrew Morton --- mm/huge_memory.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 03fd4bc39ea1..5734d5d5060f 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3790,7 +3790,9 @@ static unsigned long deferred_split_scan(struct shrinker *shrink, * in the case it was underused, then consider it used and * don't add it back to split_queue. */ - if (!did_split && !folio_test_partially_mapped(folio)) { + if (did_split) { + ; /* folio already removed from list */ + } else if (!folio_test_partially_mapped(folio)) { list_del_init(&folio->_deferred_list); removed++; } else {