[PATCH 20/53] selftests/mm: add atexit() and signal handlers to thp_settings

Mike Rapoport
2026-04-06T14:19:46Z

khugepaged registers atexit() and signal handlers that ensure that THP
settings are restored regardless of how the test exited.

Make these handlers available for all users of thp_settings.

The call to thp_save_settings() installs thp_restore_settings as the
atexit() callback and makes sure that signals that kill a process would
still call exit() and atexit() callback.

Update child process in tests using thp_settings to use _exit() instead
of exit() to avoid altering THP settings in the middle of a test.

Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
tools/testing/selftests/mm/cow.c | 21 +++++------
tools/testing/selftests/mm/khugepaged.c | 40 +++------------------
tools/testing/selftests/mm/thp_settings.c | 28 ++++++++++++++-
tools/testing/selftests/mm/uffd-wp-mremap.c | 4 ---
4 files changed, 39 insertions(+), 54 deletions(-)

diff --git a/tools/testing/selftests/mm/cow.c b/tools/testing/selftests/mm/cow.c
index d9c69c04b67d..6abdcb30aba8 100644
--- a/tools/testing/selftests/mm/cow.c
+++ b/tools/testing/selftests/mm/cow.c
@@ -202,7 +202,7 @@ static void do_test_cow_in_parent(char *mem, size_t size, bool do_mprotect,
log_test_result(KSFT_FAIL);
goto close_comm_pipes;
} else if (!ret) {
- exit(fn(mem, size, &comm_pipes));
+ _exit(fn(mem, size, &comm_pipes));
}

while (read(comm_pipes.child_ready[0], &buf, 1) != 1)
@@ -333,7 +333,7 @@ static void do_test_vmsplice_in_parent(char *mem, size_t size,
;
/* Modify page content in the child. */
memset(mem, 0xff, size);
- exit(0);
+ _exit(0);
}

if (!before_fork) {
@@ -480,7 +480,7 @@ static void do_test_iouring(char *mem, size_t size, bool use_fork)
write(comm_pipes.child_ready[1], "0", 1);
while (read(comm_pipes.parent_ready[0], &buf, 1) != 1)
;
- exit(0);
+ _exit(0);
}

while (read(comm_pipes.child_ready[0], &buf, 1) != 1)
@@ -645,7 +645,7 @@ static void do_test_ro_pin(char *mem, size_t size, enum ro_pin_test test,
write(comm_pipes.child_ready[1], "0", 1);
while (read(comm_pipes.parent_ready[0], &buf, 1) != 1)
;
- exit(0);
+ _exit(0);
}

/* Wait until our child is ready. */
@@ -956,7 +956,7 @@ static void do_run_with_thp(test_fn fn, enum thp_run thp_run, size_t thpsize)
log_test_result(KSFT_FAIL);
goto munmap;
} else if (!ret) {
- exit(0);
+ _exit(0);
}
wait(&ret);
/* Allow for sharing all pages again. */
@@ -1347,13 +1347,13 @@ static void do_test_anon_thp_collapse(char *mem, size_t size,
switch (test) {
case ANON_THP_COLLAPSE_UNSHARED:
case ANON_THP_COLLAPSE_FULLY_SHARED:
- exit(child_memcmp_fn(mem, size, &comm_pipes));
+ _exit(child_memcmp_fn(mem, size, &comm_pipes));
break;
case ANON_THP_COLLAPSE_LOWER_SHARED:
- exit(child_memcmp_fn(mem, size / 2, &comm_pipes));
+ _exit(child_memcmp_fn(mem, size / 2, &comm_pipes));
break;
case ANON_THP_COLLAPSE_UPPER_SHARED:
- exit(child_memcmp_fn(mem + size / 2, size / 2,
+ _exit(child_memcmp_fn(mem + size / 2, size / 2,
&comm_pipes));
break;
default:
@@ -1911,10 +1911,5 @@ int main(int argc, char **argv)
run_anon_thp_test_cases();
run_non_anon_test_cases();

- if (pmdsize) {
- /* Only if THP is supported. */
- thp_restore_settings();
- }
-
ksft_finished();
}
diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index ba0a9e14e600..fac11b7e7443 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -72,7 +72,6 @@ struct file_info {
};

static struct file_info finfo;
-static bool skip_settings_restore;
static int exit_status;

static void success(const char *msg)
@@ -92,25 +91,6 @@ static void skip(const char *msg)
exit_status = KSFT_SKIP;
}

-static void restore_settings_atexit(void)
-{
- if (skip_settings_restore)
- return;
-
- ksft_print_msg("Restore THP and khugepaged settings...");
- thp_restore_settings();
- success("OK");
-
- skip_settings_restore = true;
- ksft_finished();
-}
-
-static void restore_settings(int sig)
-{
- /* exit() will invoke the restore_settings_atexit handler. */
- exit(sig ? KSFT_FAIL : exit_status);
-}
-
static void save_settings(void)
{
ksft_print_msg("Save THP and khugepaged settings...");
@@ -119,12 +99,6 @@ static void save_settings(void)
thp_save_settings();

success("OK");
-
- atexit(restore_settings_atexit);
- signal(SIGTERM, restore_settings);
- signal(SIGINT, restore_settings);
- signal(SIGHUP, restore_settings);
- signal(SIGQUIT, restore_settings);
}

static void get_finfo(const char *dir)
@@ -840,8 +814,6 @@ static void collapse_fork(struct collapse_context *c, struct mem_ops *ops)
ksft_print_msg("Share small page over fork()...");
if (!fork()) {
/* Do not touch settings on child exit */
- skip_settings_restore = true;
-
if (ops->check_huge(p, 0))
success("OK");
else
@@ -853,7 +825,7 @@ static void collapse_fork(struct collapse_context *c, struct mem_ops *ops)

validate_memory(p, 0, page_size);
ops->cleanup_area(p, hpage_pmd_size);
- exit(exit_status);
+ _exit(exit_status);
}

wait(&wstatus);
@@ -878,8 +850,6 @@ static void collapse_fork_compound(struct collapse_context *c, struct mem_ops *o
ksft_print_msg("Share huge page over fork()...");
if (!fork()) {
/* Do not touch settings on child exit */
- skip_settings_restore = true;
-
if (ops->check_huge(p, 1))
success("OK");
else
@@ -902,7 +872,7 @@ static void collapse_fork_compound(struct collapse_context *c, struct mem_ops *o

validate_memory(p, 0, hpage_pmd_size);
ops->cleanup_area(p, hpage_pmd_size);
- exit(exit_status);
+ _exit(exit_status);
}

wait(&wstatus);
@@ -928,8 +898,6 @@ static void collapse_max_ptes_shared(struct collapse_context *c, struct mem_ops
ksft_print_msg("Share huge page over fork()...");
if (!fork()) {
/* Do not touch settings on child exit */
- skip_settings_restore = true;
-
if (ops->check_huge(p, 1))
success("OK");
else
@@ -962,7 +930,7 @@ static void collapse_max_ptes_shared(struct collapse_context *c, struct mem_ops

validate_memory(p, 0, hpage_pmd_size);
ops->cleanup_area(p, hpage_pmd_size);
- exit(exit_status);
+ _exit(exit_status);
}

wait(&wstatus);
@@ -1258,5 +1226,5 @@ int main(int argc, char **argv)
t->fn(t->ctx, t->ops);
}

- restore_settings(0);
+ ksft_finished();
}
diff --git a/tools/testing/selftests/mm/thp_settings.c b/tools/testing/selftests/mm/thp_settings.c
index e748ebfb3d4e..f38ba8a27b30 100644
--- a/tools/testing/selftests/mm/thp_settings.c
+++ b/tools/testing/selftests/mm/thp_settings.c
@@ -1,6 +1,7 @@
// SPDX-License-Identifier: GPL-2.0
#include <fcntl.h>
#include <limits.h>
+#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
@@ -15,6 +16,7 @@ static struct thp_settings settings_stack[MAX_SETTINGS_DEPTH];
static int settings_index;
static struct thp_settings saved_settings;
static char dev_queue_read_ahead_path[PATH_MAX];
+static bool thp_settings_saved;

static const char * const thp_enabled_strings[] = {
"never",
@@ -298,12 +300,36 @@ void thp_pop_settings(void)

void thp_restore_settings(void)
{
- thp_write_settings(&saved_settings);
+ if (thp_settings_saved)
+ thp_write_settings(&saved_settings);
+}
+
+static void thp_restore_settings_atexit(void)
+{
+ thp_restore_settings();
+}
+
+static void thp_restore_settings_sighandler(int sig)
+{
+ /* exit() will invoke the thp_restore_settings_atexit handler. */
+ exit(KSFT_FAIL);
}

void thp_save_settings(void)
{
thp_read_settings(&saved_settings);
+
+ /*
+ * setup exit hooks to make sure THP settings are restored on graceful
+ * and error exits and signals
+ */
+ atexit(thp_restore_settings_atexit);
+ signal(SIGTERM, thp_restore_settings_sighandler);
+ signal(SIGINT, thp_restore_settings_sighandler);
+ signal(SIGHUP, thp_restore_settings_sighandler);
+ signal(SIGQUIT, thp_restore_settings_sighandler);
+
+ thp_settings_saved = true;
}

void thp_set_read_ahead_path(char *path)
diff --git a/tools/testing/selftests/mm/uffd-wp-mremap.c b/tools/testing/selftests/mm/uffd-wp-mremap.c
index 17186d4a4147..516c35d236e1 100644
--- a/tools/testing/selftests/mm/uffd-wp-mremap.c
+++ b/tools/testing/selftests/mm/uffd-wp-mremap.c
@@ -368,10 +368,6 @@ int main(int argc, char **argv)
tc->swapout, tc->hugetlb);
}

- /* If THP is supported, restore original THP settings. */
- if (nr_thpsizes)
- thp_restore_settings();
-
i = ksft_get_fail_cnt();
if (i)
ksft_exit_fail_msg("%d out of %d tests failed\n",
--
2.53.0