Re: [PATCH] selftests/mm: skip hugetlb_dio tests when DIO alignment is incompatible

[Mike Rapoport <rppt@kernel.org>]

On Fri, Mar 27, 2026 at 11:12:43AM +0800, Li Wang wrote:
> hugetlb_dio test uses sub-page offsets (pagesize / 2) to verify that
> hugepages used as DIO user buffers are correctly unpinned at completion.
> 
> However, on filesystems with a logical block size larger than half the
> page size (e.g., 4K-sector block devices), these unaligned DIO writes
> are rejected with -EINVAL, causing the test to fail unexpectedly.
> 
> Add check_dio_alignment() which queries the filesystem's DIO alignment
> requirement via statx(STATX_DIOALIGN) and skips the test early if the
> sub-page offset used by the test is not compatible with the alignment
> constraint.
> 
> === Reproduce Steps ===
> 
>   # dd if=/dev/zero of=/tmp/test.img bs=1M count=512
>   # losetup --sector-size 4096 /dev/loop0 /tmp/test.img
>   # mkfs.xfs /dev/loop0
>   # mkdir -p /mnt/dio_test
>   # mount /dev/loop0 /mnt/dio_test
> 
>   // Modify test to open /mnt/dio_test and rebuild it:
>   -       fd = open("/tmp", O_TMPFILE | O_RDWR | O_DIRECT, 0664);
>   +       fd = open("/mnt/dio_test", O_TMPFILE | O_RDWR | O_DIRECT, 0664);
> 
>   # getconf PAGESIZE
>   4096
> 
>   # echo 100 >/proc/sys/vm/nr_hugepages
> 
>   # ./hugetlb_dio
>   TAP version 13
>   1..4
>   # No. Free pages before allocation : 100
>   # No. Free pages after munmap : 100
>   ok 1 free huge pages from 0-12288
>   Bail out! Error writing to file
>   : Invalid argument (22)
>   # Planned tests != run tests (4 != 1)
>   # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
> 
> Signed-off-by: Li Wang <liwang@redhat.com>
> ---
>  tools/testing/selftests/mm/hugetlb_dio.c | 37 +++++++++++++++++-------
>  1 file changed, 27 insertions(+), 10 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/hugetlb_dio.c b/tools/testing/selftests/mm/hugetlb_dio.c
> index 9ac62eb4c97d..afcca50d190e 100644
> --- a/tools/testing/selftests/mm/hugetlb_dio.c
> +++ b/tools/testing/selftests/mm/hugetlb_dio.c
> @@ -20,6 +20,31 @@
>  #include "vm_util.h"
>  #include "kselftest.h"
>  
> +#ifndef STATX_DIOALIGN
> +#define STATX_DIOALIGN		0x00002000U
> +#endif
> +
> +void check_dio_alignment(size_t pagesize)
> +{
> +	int fd;
> +	struct statx stx;
> +	unsigned int dio_align = 1;
> +
> +	fd = open("/tmp", O_TMPFILE | O_RDWR, 0664);
> +	if (fd < 0)
> +		ksft_exit_skip("Unable to allocate file: %s\n", strerror(errno));
> +
> +	if (statx(fd, "", AT_EMPTY_PATH, STATX_DIOALIGN, &stx) == 0 &&
> +				(stx.stx_mask & STATX_DIOALIGN))
> +		dio_align = stx.stx_dio_offset_align;
> +
> +	close(fd);
> +
> +	if ((pagesize / 2) % dio_align != 0)
> +		ksft_exit_skip("DIO alignment (%u) incompatible with sub-page offset %lu\n",
> +				dio_align, pagesize / 2);

This also needlessly skips the test with aligned offsets.

I'd suggest detecting dio_align here, passing it to run_dio_using_hugetlb()
and moving the check that skips a test there.

> +}
> +
>  void run_dio_using_hugetlb(unsigned int start_off, unsigned int end_off)
>  {
>  	int fd;

-- 
Sincerely yours,
Mike.