linux-kernel - [PATCH 2/2] mm/huge_memory: skip invalid debugfs new

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Date: Thu,  7 Mar 2024 13:18:54 -0500
From: Zi Yan <zi.yan@...t.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm@...ck.org
Cc: Zi Yan <ziy@...dia.com>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	"Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	David Hildenbrand <david@...hat.com>,
	Yang Shi <shy828301@...il.com>,
	Yu Zhao <yuzhao@...gle.com>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Ryan Roberts <ryan.roberts@....com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] mm/huge_memory: skip invalid debugfs new_order input for folio split

From: Zi Yan <ziy@...dia.com>

User can put arbitrary new_order via debugfs for folio split test. Although
new_order check is added to split_huge_page_to_list_order() in the prior
commit, these two additional checks can avoid unnecessary folio locking
and split_folio_to_order() calls.

Link: https://lore.kernel.org/linux-mm/7dda9283-b437-4cf8-ab0d-83c330deb9c0@moroto.mountain/
Signed-off-by: Zi Yan <ziy@...dia.com>
---
 mm/huge_memory.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 57fca7bffd20..9859aa4f7553 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3486,6 +3486,9 @@ static int split_huge_pages_pid(int pid, unsigned long vaddr_start,
 		if (!is_transparent_hugepage(folio))
 			goto next;
 
+		if (new_order >= folio_order(folio))
+			goto next;
+
 		total++;
 		/*
 		 * For folios with private, split_huge_page_to_list_to_order()
@@ -3553,6 +3556,9 @@ static int split_huge_pages_in_file(const char *file_path, pgoff_t off_start,
 		total++;
 		nr_pages = folio_nr_pages(folio);
 
+		if (new_order >= folio_order(folio))
+			goto next;
+
 		if (!folio_trylock(folio))
 			goto next;
 
-- 
2.43.0