Re: [PATCH v3 4/5] selftests/mm: protection_keys: save/restore nr_hugepages settings

[Joey Gouly <joey.gouly@arm.com>]

Hi Muhammad,

On Thu, Jan 25, 2024 at 08:46:07PM +0500, Muhammad Usama Anjum wrote:
> Save and restore nr_hugepages before changing it during the test. A test
> should not change system wide settings.
> 
> Fixes: 5f23f6d082a9 ("x86/pkeys: Add self-tests")
> Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
> ---
>  tools/testing/selftests/mm/protection_keys.c | 34 ++++++++++++++++++++
>  1 file changed, 34 insertions(+)
> 
> diff --git a/tools/testing/selftests/mm/protection_keys.c b/tools/testing/selftests/mm/protection_keys.c
> index 48dc151f8fca8..f822ae31af22e 100644
> --- a/tools/testing/selftests/mm/protection_keys.c
> +++ b/tools/testing/selftests/mm/protection_keys.c
> @@ -54,6 +54,7 @@ int test_nr;
>  u64 shadow_pkey_reg;
>  int dprint_in_signal;
>  char dprint_in_signal_buffer[DPRINT_IN_SIGNAL_BUF_SIZE];
> +char buf[256];
>  
>  void cat_into_file(char *str, char *file)
>  {
> @@ -1744,6 +1745,38 @@ void pkey_setup_shadow(void)
>  	shadow_pkey_reg = __read_pkey_reg();
>  }
>  
> +void restore_settings_atexit(void)
> +{
> +	cat_into_file(buf, "/proc/sys/vm/nr_hugepages");
> +}
> +
> +void save_settings(void)
> +{
> +	int fd;
> +	int err;
> +
> +	if (geteuid())
> +		return;
> +
> +	fd = open("/proc/sys/vm/nr_hugepages", O_RDONLY);
> +	if (fd < 0) {
> +		fprintf(stderr, "error opening\n");
> +		perror("error: ");
> +		exit(__LINE__);
> +	}
> +
> +	/* -1 to guarantee leaving the trailing \0 */
> +	err = read(fd, buf, sizeof(buf)-1);
> +	if (err < 0) {
> +		fprintf(stderr, "error reading\n");
> +		perror("error: ");
> +		exit(__LINE__);
> +	}
> +
> +	atexit(restore_settings_atexit);
> +	close(fd);
> +}
> +
>  int main(void)
>  {
>  	int nr_iterations = 22;
> @@ -1751,6 +1784,7 @@ int main(void)
>  
>  	srand((unsigned int)time(NULL));
>  
> +	save_settings();
>  	setup_handlers();
>  
>  	printf("has pkeys: %d\n", pkeys_supported);
> -- 
> 2.42.0
> 

This break the tests for me:

assert() at protection_keys.c::812 test_nr: 19 iteration: 1
running abort_hooks()...

This is because some of the tests fork, so on their atexit() they will set the
nr_hugepages back to the previous setting. Specifically the
test_pkey_alloc_exhaust() test.

Thanks,
Joey