linux-kernel - [PATCH v2 6/8] selftests/mm: fix faulting-in code in pagemap

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Message-ID: <20260107164842.3289559-7-kevin.brodsky@arm.com>
Date: Wed,  7 Jan 2026 16:48:40 +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>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Mark Brown <broonie@...nel.org>,
	Ryan Roberts <ryan.roberts@....com>,
	Shuah Khan <shuah@...nel.org>,
	Usama Anjum <Usama.Anjum@....com>
Subject: [PATCH v2 6/8] selftests/mm: fix faulting-in code in pagemap_ioctl test

One of the pagemap_ioctl tests attempts to fault in pages by
memcpy()'ing them to an unused buffer. This probably worked
originally, but since commit 46036188ea1f ("selftests/mm: build with
-O2") the compiler is free to optimise away that unused buffer and
the memcpy() with it. As a result there might not be any resident
page in the mapping and the test may fail.

We don't need to copy all that memory anyway. Just fault in every
page.

Cc: Usama Anjum <Usama.Anjum@....com>
Signed-off-by: Kevin Brodsky <kevin.brodsky@....com>
---
 tools/testing/selftests/mm/pagemap_ioctl.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/tools/testing/selftests/mm/pagemap_ioctl.c b/tools/testing/selftests/mm/pagemap_ioctl.c
index 2cb5441f29c7..80d7c391f8f5 100644
--- a/tools/testing/selftests/mm/pagemap_ioctl.c
+++ b/tools/testing/selftests/mm/pagemap_ioctl.c
@@ -1056,7 +1056,6 @@ int sanity_tests(void)
 	struct page_region *vec;
 	char *mem, *fmem;
 	struct stat sbuf;
-	char *tmp_buf;
 
 	/* 1. wrong operation */
 	mem_size = 10 * page_size;
@@ -1167,8 +1166,7 @@ int sanity_tests(void)
 	if (fmem == MAP_FAILED)
 		ksft_exit_fail_msg("error nomem %d %s\n", errno, strerror(errno));
 
-	tmp_buf = malloc(sbuf.st_size);
-	memcpy(tmp_buf, fmem, sbuf.st_size);
+	force_read_pages_in_range(fmem, sbuf.st_size);
 
 	ret = pagemap_ioctl(fmem, sbuf.st_size, vec, vec_size, 0, 0,
 			    0, PAGEMAP_NON_WRITTEN_BITS, 0, PAGEMAP_NON_WRITTEN_BITS);
-- 
2.51.2