1 files changed, 305 insertions, 0 deletions
diff --git a/tools/testing/selftests/futex/functional/futex_priv_hash.c b/tools/testing/selftests/futex/functional/futex_priv_hash.c
new file mode 100644
index 000000000000..aea001ac4946
--- /dev/null
+++ b/tools/testing/selftests/futex/functional/futex_priv_hash.c
@@ -0,0 +1,305 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2025 Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+ */
+
+#define _GNU_SOURCE
+
+#include <errno.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include <linux/prctl.h>
+#include <sys/prctl.h>
+
+#include "logging.h"
+
+#define MAX_THREADS	64
+
+static pthread_barrier_t barrier_main;
+static pthread_mutex_t global_lock;
+static pthread_t threads[MAX_THREADS];
+static int counter;
+
+#ifndef PR_FUTEX_HASH
+#define PR_FUTEX_HASH			78
+# define PR_FUTEX_HASH_SET_SLOTS	1
+# define PR_FUTEX_HASH_GET_SLOTS	2
+#endif
+
+static int futex_hash_slots_set(unsigned int slots)
+{
+	return prctl(PR_FUTEX_HASH, PR_FUTEX_HASH_SET_SLOTS, slots, 0);
+}
+
+static int futex_hash_slots_get(void)
+{
+	return prctl(PR_FUTEX_HASH, PR_FUTEX_HASH_GET_SLOTS);
+}
+
+static void futex_hash_slots_set_verify(int slots)
+{
+	int ret;
+
+	ret = futex_hash_slots_set(slots);
+	if (ret != 0) {
+		ksft_test_result_fail("Failed to set slots to %d: %m\n", slots);
+		ksft_finished();
+	}
+	ret = futex_hash_slots_get();
+	if (ret != slots) {
+		ksft_test_result_fail("Set %d slots but PR_FUTEX_HASH_GET_SLOTS returns: %d, %m\n",
+		       slots, ret);
+		ksft_finished();
+	}
+	ksft_test_result_pass("SET and GET slots %d passed\n", slots);
+}
+
+static void futex_hash_slots_set_must_fail(int slots)
+{
+	int ret;
+
+	ret = futex_hash_slots_set(slots);
+	ksft_test_result(ret < 0, "futex_hash_slots_set(%d)\n",
+			 slots);
+}
+
+static void *thread_return_fn(void *arg)
+{
+	return NULL;
+}
+
+static void *thread_lock_fn(void *arg)
+{
+	pthread_barrier_wait(&barrier_main);
+
+	pthread_mutex_lock(&global_lock);
+	counter++;
+	usleep(20);
+	pthread_mutex_unlock(&global_lock);
+	return NULL;
+}
+
+static void create_max_threads(void *(*thread_fn)(void *))
+{
+	int i, ret;
+
+	for (i = 0; i < MAX_THREADS; i++) {
+		ret = pthread_create(&threads[i], NULL, thread_fn, NULL);
+		if (ret)
+			ksft_exit_fail_msg("pthread_create failed: %m\n");
+	}
+}
+
+static void join_max_threads(void)
+{
+	int i, ret;
+
+	for (i = 0; i < MAX_THREADS; i++) {
+		ret = pthread_join(threads[i], NULL);
+		if (ret)
+			ksft_exit_fail_msg("pthread_join failed for thread %d\n", i);
+	}
+}
+
+#define SEC_IN_NSEC	1000000000
+#define MSEC_IN_NSEC	1000000
+
+static void futex_dummy_op(void)
+{
+	pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
+	struct timespec timeout;
+	int ret;
+
+	pthread_mutex_lock(&lock);
+	clock_gettime(CLOCK_REALTIME, &timeout);
+	timeout.tv_nsec += 100 * MSEC_IN_NSEC;
+	if (timeout.tv_nsec >=  SEC_IN_NSEC) {
+		timeout.tv_nsec -= SEC_IN_NSEC;
+		timeout.tv_sec++;
+	}
+	ret = pthread_mutex_timedlock(&lock, &timeout);
+	if (ret == 0)
+		ksft_exit_fail_msg("Successfully locked an already locked mutex.\n");
+
+	if (ret != ETIMEDOUT)
+		ksft_exit_fail_msg("pthread_mutex_timedlock() did not timeout: %d.\n", ret);
+}
+
+static void usage(char *prog)
+{
+	printf("Usage: %s\n", prog);
+	printf("  -c    Use color\n");
+	printf("  -g    Test global hash instead intead local immutable \n");
+	printf("  -h    Display this help message\n");
+	printf("  -v L  Verbosity level: %d=QUIET %d=CRITICAL %d=INFO\n",
+	       VQUIET, VCRITICAL, VINFO);
+}
+
+static const char *test_msg_auto_create = "Automatic hash bucket init on thread creation.\n";
+static const char *test_msg_auto_inc = "Automatic increase with more than 16 CPUs\n";
+
+int main(int argc, char *argv[])
+{
+	int futex_slots1, futex_slotsn, online_cpus;
+	pthread_mutexattr_t mutex_attr_pi;
+	int ret, retry = 20;
+	int c;
+
+	while ((c = getopt(argc, argv, "chv:")) != -1) {
+		switch (c) {
+		case 'c':
+			log_color(1);
+			break;
+		case 'h':
+			usage(basename(argv[0]));
+			exit(0);
+			break;
+		case 'v':
+			log_verbosity(atoi(optarg));
+			break;
+		default:
+			usage(basename(argv[0]));
+			exit(1);
+		}
+	}
+
+	ksft_print_header();
+	ksft_set_plan(21);
+
+	ret = pthread_mutexattr_init(&mutex_attr_pi);
+	ret |= pthread_mutexattr_setprotocol(&mutex_attr_pi, PTHREAD_PRIO_INHERIT);
+	ret |= pthread_mutex_init(&global_lock, &mutex_attr_pi);
+	if (ret != 0) {
+		ksft_exit_fail_msg("Failed to initialize pthread mutex.\n");
+	}
+	/* First thread, expect to be 0, not yet initialized */
+	ret = futex_hash_slots_get();
+	if (ret != 0)
+		ksft_exit_fail_msg("futex_hash_slots_get() failed: %d, %m\n", ret);
+
+	ksft_test_result_pass("Basic get slots and immutable status.\n");
+	ret = pthread_create(&threads[0], NULL, thread_return_fn, NULL);
+	if (ret != 0)
+		ksft_exit_fail_msg("pthread_create() failed: %d, %m\n", ret);
+
+	ret = pthread_join(threads[0], NULL);
+	if (ret != 0)
+		ksft_exit_fail_msg("pthread_join() failed: %d, %m\n", ret);
+
+	/* First thread, has to initialiaze private hash */
+	futex_slots1 = futex_hash_slots_get();
+	if (futex_slots1 <= 0) {
+		ksft_print_msg("Current hash buckets: %d\n", futex_slots1);
+		ksft_exit_fail_msg(test_msg_auto_create);
+	}
+
+	ksft_test_result_pass(test_msg_auto_create);
+
+	online_cpus = sysconf(_SC_NPROCESSORS_ONLN);
+	ret = pthread_barrier_init(&barrier_main, NULL, MAX_THREADS + 1);
+	if (ret != 0)
+		ksft_exit_fail_msg("pthread_barrier_init failed: %m.\n");
+
+	ret = pthread_mutex_lock(&global_lock);
+	if (ret != 0)
+		ksft_exit_fail_msg("pthread_mutex_lock failed: %m.\n");
+
+	counter = 0;
+	create_max_threads(thread_lock_fn);
+	pthread_barrier_wait(&barrier_main);
+
+	/*
+	 * The current default size of hash buckets is 16. The auto increase
+	 * works only if more than 16 CPUs are available.
+	 */
+	ksft_print_msg("Online CPUs: %d\n", online_cpus);
+	if (online_cpus > 16) {
+retry_getslots:
+		futex_slotsn = futex_hash_slots_get();
+		if (futex_slotsn < 0 || futex_slots1 == futex_slotsn) {
+			retry--;
+			/*
+			 * Auto scaling on thread creation can be slightly delayed
+			 * because it waits for a RCU grace period twice. The new
+			 * private hash is assigned upon the first futex operation
+			 * after grace period.
+			 * To cover all this for testing purposes the function
+			 * below will acquire a lock and acquire it again with a
+			 * 100ms timeout which must timeout. This ensures we
+			 * sleep for 100ms and issue a futex operation.
+			 */
+			if (retry > 0) {
+				futex_dummy_op();
+				goto retry_getslots;
+			}
+			ksft_print_msg("Expected increase of hash buckets but got: %d -> %d\n",
+				       futex_slots1, futex_slotsn);
+			ksft_exit_fail_msg(test_msg_auto_inc);
+		}
+		ksft_test_result_pass(test_msg_auto_inc);
+	} else {
+		ksft_test_result_skip(test_msg_auto_inc);
+	}
+	ret = pthread_mutex_unlock(&global_lock);
+
+	/* Once the user changes it, it has to be what is set */
+	futex_hash_slots_set_verify(2);
+	futex_hash_slots_set_verify(4);
+	futex_hash_slots_set_verify(8);
+	futex_hash_slots_set_verify(32);
+	futex_hash_slots_set_verify(16);
+
+	ret = futex_hash_slots_set(15);
+	ksft_test_result(ret < 0, "Use 15 slots\n");
+
+	futex_hash_slots_set_verify(2);
+	join_max_threads();
+	ksft_test_result(counter == MAX_THREADS, "Created of waited for %d of %d threads\n",
+			 counter, MAX_THREADS);
+	counter = 0;
+	/* Once the user set something, auto reisze must be disabled */
+	ret = pthread_barrier_init(&barrier_main, NULL, MAX_THREADS);
+
+	create_max_threads(thread_lock_fn);
+	join_max_threads();
+
+	ret = futex_hash_slots_get();
+	ksft_test_result(ret == 2, "No more auto-resize after manaul setting, got %d\n",
+			 ret);
+
+	futex_hash_slots_set_must_fail(1 << 29);
+	futex_hash_slots_set_verify(4);
+
+	/*
+	 * Once the global hash has been requested, then this requested can not
+	 * be undone.
+	 */
+	ret = futex_hash_slots_set(0);
+	ksft_test_result(ret == 0, "Global hash request\n");
+	if (ret != 0)
+		goto out;
+
+	futex_hash_slots_set_must_fail(4);
+	futex_hash_slots_set_must_fail(8);
+	futex_hash_slots_set_must_fail(8);
+	futex_hash_slots_set_must_fail(0);
+	futex_hash_slots_set_must_fail(6);
+
+	ret = pthread_barrier_init(&barrier_main, NULL, MAX_THREADS);
+	if (ret != 0) {
+		ksft_exit_fail_msg("pthread_barrier_init failed: %m\n");
+		return 1;
+	}
+	create_max_threads(thread_lock_fn);
+	join_max_threads();
+
+	ret = futex_hash_slots_get();
+	ksft_test_result(ret == 0, "Continue to use global hash\n");
+
+out:
+	ksft_finished();
+	return 0;
+}