Re: [PATCH] selftests/mm: Specify requirement for PROC_MEM_ALWAYS_FORCE=y

[Dev Jain <dev.jain@arm.com>]

On 17/04/26 12:58 am, Mike Rapoport wrote:
> On Thu, Apr 16, 2026 at 08:10:53PM +0100, Mark Brown wrote:
>> On Thu, Apr 16, 2026 at 09:05:11PM +0200, David Hildenbrand (Arm) wrote:
>>> On 4/16/26 20:40, Mark Brown wrote:
>>
>>>> Several of the mm selftests made use of /proc/pid/mem as part of their
>>>> operation but we do not specify this in the config fragment for them, at
>>>> least mkdirty and ksm_functional_tests have this requirement.
>>
>>> I guess we could teach most tests to SKIP if /proc/pid/mem is unusable.
>>
>> That would be nicer, yes.  I imagine some of these will predate there
>> being a configuration option here at all, it's possible there's newer
>> tests that skip cleanly - I didn't look at the skips.
> 
> Enabling access to /proc/pid/mem keeps the coverage, not that it's great
> right now, but still.
> 
> But sure graceful skips are better than failing the entire tests. Would be
> something like this:
> 
> diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
> index 8d874c4754f3..374b5a25f36d 100644
> --- a/tools/testing/selftests/mm/ksm_functional_tests.c
> +++ b/tools/testing/selftests/mm/ksm_functional_tests.c
> @@ -37,7 +37,6 @@ enum ksm_merge_mode {
>  	KSM_MERGE_NONE, /* PRCTL already set */
>  };
>  
> -static int mem_fd;
>  static int pages_to_scan_fd;
>  static int sleep_millisecs_fd;
>  static int pagemap_fd;
> @@ -622,10 +621,17 @@ static void test_prot_none(void)
>  {
>  	const unsigned int size = 2 * MiB;
>  	char *map;
> +	int mem_fd;
>  	int i;
>  
>  	ksft_print_msg("[RUN] %s\n", __func__);
>  
> +	mem_fd = open("/proc/self/mem", O_RDWR);
> +	if (mem_fd < 0) {
> +		ksft_test_result_skip("opening /proc/self/mem failed\n");
> +		return;
> +	}
> +
>  	map = mmap_and_merge_range(0x11, size, PROT_NONE, KSM_MERGE_MADVISE);
>  	if (map == MAP_FAILED)
>  		goto unmap;
> @@ -694,9 +700,6 @@ static void test_fork_ksm_merging_page_count(void)
>  
>  static void init_global_file_handles(void)
>  {
> -	mem_fd = open("/proc/self/mem", O_RDWR);
> -	if (mem_fd < 0)
> -		ksft_exit_fail_msg("opening /proc/self/mem failed\n");
>  	if (ksm_stop() < 0)
>  		ksft_exit_skip("accessing \"/sys/kernel/mm/ksm/run\") failed\n");
>  	if (ksm_get_full_scans() < 0)
> diff --git a/tools/testing/selftests/mm/mkdirty.c b/tools/testing/selftests/mm/mkdirty.c
> index 68dd447a5454..e4a94638018b 100644
> --- a/tools/testing/selftests/mm/mkdirty.c
> +++ b/tools/testing/selftests/mm/mkdirty.c
> @@ -27,7 +27,6 @@
>  
>  static size_t pagesize;
>  static size_t thpsize;
> -static int mem_fd;
>  static int pagemap_fd;
>  static sigjmp_buf env;
>  
> @@ -86,11 +85,18 @@ static char *mmap_thp_range(int prot, char **_mmap_mem, size_t *_mmap_size)
>  static void test_ptrace_write(void)
>  {
>  	char data = 1;
> +	int mem_fd;
>  	char *mem;
>  	int ret;
>  
>  	ksft_print_msg("[INFO] PTRACE write access\n");
>  
> +	mem_fd = open("/proc/self/mem", O_RDWR);
> +	if (mem_fd < 0) {
> +		ksft_test_result_skip("opening /proc/self/mem failed\n");
> +		return;
> +	}
> +
>  	mem = mmap(NULL, pagesize, PROT_READ, MAP_PRIVATE|MAP_ANON, -1, 0);
>  	if (mem == MAP_FAILED) {
>  		ksft_test_result_fail("mmap() failed\n");
> @@ -124,10 +130,17 @@ static void test_ptrace_write_thp(void)
>  	char *mem, *mmap_mem;
>  	size_t mmap_size;
>  	char data = 1;
> +	int mem_fd;
>  	int ret;
>  
>  	ksft_print_msg("[INFO] PTRACE write access to THP\n");
>  
> +	mem_fd = open("/proc/self/mem", O_RDWR);
> +	if (mem_fd < 0) {
> +		ksft_test_result_skip("opening /proc/self/mem failed\n");
> +		return;
> +	}
> +
>  	mem = mmap_thp_range(PROT_READ, &mmap_mem, &mmap_size);
>  	if (mem == MAP_FAILED)
>  		return;
> @@ -343,9 +356,6 @@ int main(void)
>  	ksft_print_header();
>  	ksft_set_plan(tests);
>  
> -	mem_fd = open("/proc/self/mem", O_RDWR);
> -	if (mem_fd < 0)
> -		ksft_exit_fail_msg("opening /proc/self/mem failed\n");
>  	pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
>  	if (pagemap_fd < 0)
>  		ksft_exit_fail_msg("opening /proc/self/pagemap failed\n");

Looks fine, but would be better to close the fd before function exit?

I can review if you plan to send a patch : )

> 
>>> Acked-by: David Hildenbrand (Arm) <david@kernel.org>
>>
>> Thanks.
> 
> 
>