linux-kernel - [PATCH] mm/huge_memory: drop beyond-EOF folios with the right number of refs.

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Message-ID: <20250310155727.472846-1-ziy@nvidia.com>
Date: Mon, 10 Mar 2025 11:57:27 -0400
From: Zi Yan <ziy@...dia.com>
To: linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Pankaj Raghav <p.raghav@...sung.com>
Cc: Ryan Roberts <ryan.roberts@....com>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	David Hildenbrand <david@...hat.com>,
	Yang Shi <yang@...amperecomputing.com>,
	Miaohe Lin <linmiaohe@...wei.com>,
	Kefeng Wang <wangkefeng.wang@...wei.com>,
	Yu Zhao <yuzhao@...gle.com>,
	John Hubbard <jhubbard@...dia.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	linux-kselftest@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	Zi Yan <ziy@...dia.com>,
	stable@...r.kernel.org
Subject: [PATCH] mm/huge_memory: drop beyond-EOF folios with the right number of refs.

When an after-split folio is large and needs to be dropped due to EOF,
folio_put_refs(folio, folio_nr_pages(folio)) should be used to drop
all page cache refs. Otherwise, the folio will not be freed, causing
memory leak.

This leak would happen on a filesystem with blocksize > page_size and
a truncate is performed, where the blocksize makes folios split to
>0 order ones, causing truncated folios not being freed.

Fixes: c010d47f107f ("mm: thp: split huge page to any lower order pages")
Reported-by: Hugh Dickins <hughd@...gle.com>
Closes: https://lore.kernel.org/all/fcbadb7f-dd3e-21df-f9a7-2853b53183c4@google.com/
Cc: stable@...r.kernel.org
Signed-off-by: Zi Yan <ziy@...dia.com>
---
 mm/huge_memory.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 3d3ebdc002d5..373781b21e5c 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3304,7 +3304,7 @@ static void __split_huge_page(struct page *page, struct list_head *list,
 				folio_account_cleaned(tail,
 					inode_to_wb(folio->mapping->host));
 			__filemap_remove_folio(tail, NULL);
-			folio_put(tail);
+			folio_put_refs(tail, folio_nr_pages(tail));
 		} else if (!folio_test_anon(folio)) {
 			__xa_store(&folio->mapping->i_pages, tail->index,
 					tail, 0);
-- 
2.47.2