Re: [PATCH v2 20/22] selftests/coredump: put a hole in the middle of a sparse mapping

[R Nageswara Sastry <rnsastry@linux.ibm.com>]

On 20.08.2026 4:39 AM, Christian Brauner wrote:
> The crashing_child_sparse() helper touches the first page of the
> mapping. That forces everything behind it to be a trailing hole. This is
> easy to handle. Make the test more difficult meaningful by also touchin
> the last page. This causes the hole to sit between two populated pages.
>
> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
Tested-by: R Nageswara Sastry <rnsastry@linux.ibm.com>

System: ppc64le LPAR (IBM POWER), Linux 7.3-rc2
> ---
>   tools/testing/selftests/coredump/coredump_test_helpers.c | 10 ++++++----
>   1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/tools/testing/selftests/coredump/coredump_test_helpers.c b/tools/testing/selftests/coredump/coredump_test_helpers.c
> index 45d76fa0f469..89f3954c5607 100644
> --- a/tools/testing/selftests/coredump/coredump_test_helpers.c
> +++ b/tools/testing/selftests/coredump/coredump_test_helpers.c
> @@ -58,14 +58,16 @@ void crashing_child_sparse(size_t size)
>   	char *p;
>   
>   	/*
> -	 * Touch the first page only. The whole mapping is dumped because
> -	 * it has been written to, but all of it save that one page is a
> -	 * hole.
> +	 * Touch the first and the last page. This will cause the whole mapping
> +	 * to be dumped because it has been written to. Everything between
> +	 * those two pages is a hole though.
>   	 */
>   	p = mmap(NULL, size, PROT_READ | PROT_WRITE,
>   		 MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE, -1, 0);
> -	if (p != MAP_FAILED)
> +	if (p != MAP_FAILED) {
>   		p[0] = 'x';
> +		p[size - 1] = 'x';
> +	}
>   
>   	/* crash on purpose */
>   	*(volatile int *)NULL = 0;
>
-- 
Thanks and Regards
R.Nageswara Sastry