Re: [PATCH] selftests/mm: check file initialization writes in split_huge_page_test

[Wei Yang <richard.weiyang@gmail.com>]

On Tue, May 12, 2026 at 01:19:24PM +0530, Vineet Agarwal wrote:
>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.
>
>Signed-off-by: Vineet Agarwal <agarwal.vineet2006@gmail.com>
>---
> tools/testing/selftests/mm/split_huge_page_test.c | 13 ++++++++++---
> 1 file changed, 10 insertions(+), 3 deletions(-)
>
>diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
>index 500d07c4938b..eab69b0f59a0 100644
>--- a/tools/testing/selftests/mm/split_huge_page_test.c
>+++ b/tools/testing/selftests/mm/split_huge_page_test.c
>@@ -609,9 +609,16 @@ static int create_pagecache_thp_and_fd(const char *testfile, size_t fd_size,
> 	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;

Maybe we can "goto err_out_close" and remove the close() here?

Apart from this, I found on error writing to /proc/sys/vm/drop_caches in below,
it just goto err_out_unlink, which left fd open.

How about fix that at the same time.

Generally, the change look good.

>+		}
>+	}
> 	close(*fd);
> 	sync();
> 	*fd = open("/proc/sys/vm/drop_caches", O_WRONLY);
>-- 
>2.54.0
>

-- 
Wei Yang
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