linux-kernel - [PATCH] selftests/mm: fix division-by-zero in uffd-unit-tests

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Message-ID: <20251113034623.3127012-1-cmllamas@google.com>
Date: Thu, 13 Nov 2025 03:46:22 +0000
From: Carlos Llamas <cmllamas@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>, Peter Xu <peterx@...hat.com>, 
	David Hildenbrand <david@...hat.com>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
	"Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka <vbabka@...e.cz>, 
	Mike Rapoport <rppt@...nel.org>, Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>, 
	Shuah Khan <shuah@...nel.org>, Ujwal Kundur <ujwal.kundur@...il.com>, 
	Brendan Jackman <jackmanb@...gle.com>
Cc: kernel-team@...roid.com, linux-kernel@...r.kernel.org, 
	Carlos Llamas <cmllamas@...gle.com>, stable@...r.kernel.org, 
	"open list:MEMORY MANAGEMENT - USERFAULTFD" <linux-mm@...ck.org>, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>
Subject: [PATCH] selftests/mm: fix division-by-zero in uffd-unit-tests

Commit 4dfd4bba8578 ("selftests/mm/uffd: refactor non-composite global
vars into struct") moved some of the operations previously implemented
in uffd_setup_environment() earlier in the main test loop.

The calculation of nr_pages, which involves a division by page_size, now
occurs before checking that default_huge_page_size() returns a non-zero
This leads to a division-by-zero error on systems with !CONFIG_HUGETLB.

Fix this by relocating the non-zero page_size check before the nr_pages
calculation, as it was originally implemented.

Cc: stable@...r.kernel.org
Fixes: 4dfd4bba8578 ("selftests/mm/uffd: refactor non-composite global vars into struct")
Signed-off-by: Carlos Llamas <cmllamas@...gle.com>
---
 tools/testing/selftests/mm/uffd-unit-tests.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c
index 9e3be2ee7f1b..f917b4c4c943 100644
--- a/tools/testing/selftests/mm/uffd-unit-tests.c
+++ b/tools/testing/selftests/mm/uffd-unit-tests.c
@@ -1758,10 +1758,15 @@ int main(int argc, char *argv[])
 			uffd_test_ops = mem_type->mem_ops;
 			uffd_test_case_ops = test->test_case_ops;
 
-			if (mem_type->mem_flag & (MEM_HUGETLB_PRIVATE | MEM_HUGETLB))
+			if (mem_type->mem_flag & (MEM_HUGETLB_PRIVATE | MEM_HUGETLB)) {
 				gopts.page_size = default_huge_page_size();
-			else
+				if (gopts.page_size == 0) {
+					uffd_test_skip("huge page size is 0, feature missing?");
+					continue;
+				}
+			} else {
 				gopts.page_size = psize();
+			}
 
 			/* Ensure we have at least 2 pages */
 			gopts.nr_pages = MAX(UFFD_TEST_MEM_SIZE, gopts.page_size * 2)
@@ -1776,12 +1781,6 @@ int main(int argc, char *argv[])
 				continue;
 
 			uffd_test_start("%s on %s", test->name, mem_type->name);
-			if ((mem_type->mem_flag == MEM_HUGETLB ||
-			    mem_type->mem_flag == MEM_HUGETLB_PRIVATE) &&
-			    (default_huge_page_size() == 0)) {
-				uffd_test_skip("huge page size is 0, feature missing?");
-				continue;
-			}
 			if (!uffd_feature_supported(test)) {
 				uffd_test_skip("feature missing");
 				continue;
-- 
2.51.2.1041.gc1ab5b90ca-goog