Re: [PATCH v2 6/8] selftests/mm: fix faulting-in code in pagemap_ioctl test

Dev Jain
2026-01-22T06:16:07Z

On 07/01/26 10:18 pm, Kevin Brodsky wrote:
> 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@arm.com>
> Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>

Reviewed-by: Dev Jain <dev.jain@arm.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);