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

Mike Rapoport
2026-04-16T19:28:38Z

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");

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

--
Sincerely yours,
Mike.