+ selftests-mm-check-file-initialization-writes-in-split_huge_page_test.patch added to mm-new branch

+ selftests-mm-check-file-initialization-writes-in-split_huge_page_test.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: selftests/mm: check file initialization writes in split_huge_page_test
has been added to the -mm mm-new branch.  Its filename is
     selftests-mm-check-file-initialization-writes-in-split_huge_page_test.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/selftests-mm-check-file-initialization-writes-in-split_huge_page_test.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: Vineet Agarwal <agarwal.vineet2006@gmail.com>
Subject: selftests/mm: check file initialization writes in split_huge_page_test
Date: Tue, 12 May 2026 13:19:24 +0530

create_pagecache_thp_and_fd() fills the backing file for the pagecache THP
tests using repeated write() calls, but the return value is never checked.

If a write fails or completes only partially, the test may continue with
an incompletely initialized file and produce misleading results.

Check the result of write() and fail the test if the expected number of
bytes was not written.

Link: https://lore.kernel.org/20260512074924.27721-1-agarwal.vineet2006@gmail.com
Signed-off-by: Vineet Agarwal <agarwal.vineet2006@gmail.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/testing/selftests/mm/split_huge_page_test.c |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

--- a/tools/testing/selftests/mm/split_huge_page_test.c~selftests-mm-check-file-initialization-writes-in-split_huge_page_test
+++ a/tools/testing/selftests/mm/split_huge_page_test.c
@@ -609,9 +609,16 @@ static int create_pagecache_thp_and_fd(c
 	assert(fd_size % sizeof(buf) == 0);
 	for (i = 0; i < sizeof(buf); i++)
 		buf[i] = (unsigned char)i;
-	for (i = 0; i < fd_size; i += sizeof(buf))
-		write(*fd, buf, sizeof(buf));
+	for (i = 0; i < fd_size; i += sizeof(buf)) {
+		ssize_t written;
 
+		written = write(*fd, buf, sizeof(buf));
+		if (written != sizeof(buf)) {
+			ksft_perror("write testfile");
+			close(*fd);
+			goto err_out_unlink;
+		}
+	}
 	close(*fd);
 	sync();
 	*fd = open("/proc/sys/vm/drop_caches", O_WRONLY);
_

Patches currently in -mm which might be from agarwal.vineet2006@gmail.com are

selftests-mm-khugepaged-initialize-file-contents-via-mmap.patch
mm-khugepaged-return-eagain-for-scan_page_has_private-in-madv_collapse.patch
selftests-mm-check-file-initialization-writes-in-split_huge_page_test.patch