linux-kernel - [PATCH v3 5/9] selftests/mm: check that FORCE

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Message-ID: <20260122170224.4056513-6-kevin.brodsky@arm.com>
Date: Thu, 22 Jan 2026 17:02:20 +0000
From: Kevin Brodsky <kevin.brodsky@....com>
To: linux-mm@...ck.org,
	linux-kselftest@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	Kevin Brodsky <kevin.brodsky@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...nel.org>,
	Dev Jain <dev.jain@....com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Mark Brown <broonie@...nel.org>,
	Ryan Roberts <ryan.roberts@....com>,
	Shuah Khan <shuah@...nel.org>
Subject: [PATCH v3 5/9] selftests/mm: check that FORCE_READ() succeeded

Many cow tests rely on FORCE_READ() to populate pages. Introduce a
helper to make sure that the pages are actually populated, and fail
otherwise.

Suggested-by: David Hildenbrand (Red Hat) <david@...nel.org>
Signed-off-by: Kevin Brodsky <kevin.brodsky@....com>
---
 tools/testing/selftests/mm/cow.c | 43 ++++++++++++++++++++++++--------
 1 file changed, 33 insertions(+), 10 deletions(-)

diff --git a/tools/testing/selftests/mm/cow.c b/tools/testing/selftests/mm/cow.c
index 83b3563be26b..d9c69c04b67d 100644
--- a/tools/testing/selftests/mm/cow.c
+++ b/tools/testing/selftests/mm/cow.c
@@ -75,6 +75,18 @@ static bool range_is_swapped(void *addr, size_t size)
 	return true;
 }
 
+static bool populate_page_checked(char *addr)
+{
+	bool ret;
+
+	FORCE_READ(*addr);
+	ret = pagemap_is_populated(pagemap_fd, addr);
+	if (!ret)
+		ksft_print_msg("Failed to populate page\n");
+
+	return ret;
+}
+
 struct comm_pipes {
 	int child_ready[2];
 	int parent_ready[2];
@@ -1549,8 +1561,10 @@ static void run_with_zeropage(non_anon_test_fn fn, const char *desc)
 	}
 
 	/* Read from the page to populate the shared zeropage. */
-	FORCE_READ(*mem);
-	FORCE_READ(*smem);
+	if (!populate_page_checked(mem) || !populate_page_checked(smem)) {
+		log_test_result(KSFT_FAIL);
+		goto munmap;
+	}
 
 	fn(mem, smem, pagesize);
 munmap:
@@ -1612,8 +1626,11 @@ static void run_with_huge_zeropage(non_anon_test_fn fn, const char *desc)
 	 * the first sub-page and test if we get another sub-page populated
 	 * automatically.
 	 */
-	FORCE_READ(*mem);
-	FORCE_READ(*smem);
+	if (!populate_page_checked(mem) || !populate_page_checked(smem)) {
+		log_test_result(KSFT_FAIL);
+		goto munmap;
+	}
+
 	if (!pagemap_is_populated(pagemap_fd, mem + pagesize) ||
 	    !pagemap_is_populated(pagemap_fd, smem + pagesize)) {
 		ksft_test_result_skip("Did not get THPs populated\n");
@@ -1663,8 +1680,10 @@ static void run_with_memfd(non_anon_test_fn fn, const char *desc)
 	}
 
 	/* Fault the page in. */
-	FORCE_READ(*mem);
-	FORCE_READ(*smem);
+	if (!populate_page_checked(mem) || !populate_page_checked(smem)) {
+		log_test_result(KSFT_FAIL);
+		goto munmap;
+	}
 
 	fn(mem, smem, pagesize);
 munmap:
@@ -1719,8 +1738,10 @@ static void run_with_tmpfile(non_anon_test_fn fn, const char *desc)
 	}
 
 	/* Fault the page in. */
-	FORCE_READ(*mem);
-	FORCE_READ(*smem);
+	if (!populate_page_checked(mem) || !populate_page_checked(smem)) {
+		log_test_result(KSFT_FAIL);
+		goto munmap;
+	}
 
 	fn(mem, smem, pagesize);
 munmap:
@@ -1773,8 +1794,10 @@ static void run_with_memfd_hugetlb(non_anon_test_fn fn, const char *desc,
 	}
 
 	/* Fault the page in. */
-	FORCE_READ(*mem);
-	FORCE_READ(*smem);
+	if (!populate_page_checked(mem) || !populate_page_checked(smem)) {
+		log_test_result(KSFT_FAIL);
+		goto munmap;
+	}
 
 	fn(mem, smem, hugetlbsize);
 munmap:
-- 
2.51.2