Re: [PATCH] selftests/mm: thuge-gen: fix test_shmget() for PAGE_SIZE check

[Lorenzo Stoakes (ARM)]

On Sun, Aug 09, 2026 at 11:03:35AM +0300, Mike Rapoport (Microsoft) wrote:
> Commit 49a4e7186b08 ("selftests/mm: thuge-gen: add setup of HugeTLB pages")
> changed thuge-gen test to use common functions for reading hugetlb
> attributes from sysfs, but it missed that the original read_free() function
> special cased PAGE_SIZE tests.
>
> For PAGE_SIZE tests, failure to read sysfs was ignored and read_free()
> returned 0.
>
> This allowed test_shmget() to essentially skip the check of how many huge
> pages was consumed when it ran with PAGE_SIZE.
>
> Commit 3199b0c09efa ("selftests/mm: fix read_file() return value check")
> fixed the common read_file() to actually return error on failure and this
> exposed the issue in test_shmget() that checks the number of free hugetlb
> pages even for PAGE_SIZE test, tries to access
>
> /sys/kernel/mm/hugepages/hugepages-<PAGE_SIZE>/free_hugepages
>
> and obviously fails there.
>
> Gate the checks for free huge pages on size != getpagesize() and initialize
> before and after variables to values matching PAGE_SIZE test.
>
> Fixes: 49a4e7186b08 ("selftests/mm: thuge-gen: add setup of HugeTLB pages")
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>

With the issue Sarthak brought up addressed, LGTM, so:

Acked-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>

> ---
> selftests/mm: thuge-gen: fix test_shmget() for PAGE_SIZE check
> ---
>  tools/testing/selftests/mm/thuge-gen.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/thuge-gen.c b/tools/testing/selftests/mm/thuge-gen.c
> index 22b9c2f1c35d..50d0805b65db 100644
> --- a/tools/testing/selftests/mm/thuge-gen.c
> +++ b/tools/testing/selftests/mm/thuge-gen.c
> @@ -71,12 +71,16 @@ void test_mmap(unsigned long size, unsigned flags)
>
>  void test_shmget(unsigned long size, unsigned flags)
>  {
> -	int id;
> -	unsigned long before, after;
> +	/* values for PAGE_SIZE test */
> +	unsigned long before = NUM_PAGES;
> +	unsigned long after = 0;
>  	struct shm_info i;
>  	char *map;
> +	int id;
> +
> +	if (size != getpagesize())
> +		before = hugetlb_free_pages(size);
>
> -	before = hugetlb_free_pages(size);
>  	id = shmget(IPC_PRIVATE, size * NUM_PAGES, IPC_CREAT|0600|flags);
>  	if (id < 0) {
>  		if (errno == EPERM) {
> @@ -97,10 +101,11 @@ void test_shmget(unsigned long size, unsigned flags)
>  	shmctl(id, IPC_RMID, NULL);
>
>  	memset(map, 0xff, size*NUM_PAGES);
> -	after = hugetlb_free_pages(size);
> +	if (size != getpagesize())
> +		after = hugetlb_free_pages(size);
>
>  	show(size);
> -	ksft_test_result(size == getpagesize() || (before - after) == NUM_PAGES,
> +	ksft_test_result((before - after) == NUM_PAGES,
>  			 "%s: mmap %lu %x\n", __func__, size, flags);
>  	if (shmdt(map))
>  		ksft_exit_fail_msg("%s: shmdt: %s\n", __func__, strerror(errno));
>
> ---
> base-commit: 17e5919bdca144d4e67337f53bf57d7811f62192
> change-id: 20260809-selftests-thuge-gen-fix-5ac05f56307c
>
> --
> Sincerely yours,
> Mike.
>

--
Cheers, Lorenzo