Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Fix error output of boot instance creation failure

   Currently if a boot instance creation fails, instead of printing out
   the name of the instance that failed, it prints "(null)". That is
   because it prints "cur_str" that had already been processed by
   strsep(). Print the saved name instead.

   While at it, print the error code of the failure.

 - Fix use-after-free for same named historgrams

   Histograms can be named so that they can be used in multiple events.
   But if the named histogram has a variable attached, the second event
   that uses the named histogram which duplicates it and needs to free
   the original after duplication leaves the old variable in place and
   still visible. If another histogram uses than variable, it will use
   the stale one which will try to reference the freed duplicate
   histogram and crash the kernel.

   Free the duplicate variables along with the duplicated histogram
   data.

 - Check return value of kthread_run() in event self test

   The events self tests uses a kthread for testing but does not check
   if it succeeded in creating a kthread. If the kthread creation were
   to fail, the code will still try to call kthread_stop() on the error
   returned.

 - Fix race between reading trace_pipe and updating subbuffer size

   If a user is reading the trace_pipe file at the same time they update
   the ring buffer sub-buffer size, can cause the trace_pipe read to
   read stale data. Add trace_access_lock() around updating the ring
   buffer sub-buffer size.

 - Fix eventfs_inode on failure path in creation of the events directory

   In the creation of the "events" directory, if after allocating the
   eventfs_inode a failure is detected, it calls cleanup_ei() which
   calls free_ei(). The free_ei() will test if eventfs_inode being freed
   has no children. It is a bug if it does. But on the failure case of
   the creation of the "events" directory, the children lists have not
   yet been initialized and the free will trigger a warning because
   list_empty() on an uninitialized list returns false.

   Move the initialization into init_ei() where it makes more sense and
   makes sure that a created eventfs_inode has its lists initialized
   upon creation.

 - Check return value of kthread_run() in ftrace direct sample code

   The sample code that shows how to use the ftrace direct calls does
   not test the return of kthread_run() to see if it succeeds. Return a
   failure if the kthread_run() doesn't succeed.

 - Clear user events state on fork in case of alloc failure

   On fork, the child gets a pointer to the parent's user events state.
   It makes a copy of it then updates the child's pointer to it. But if
   the allocation fails, the duplication function leaves the child with
   a pointer to its parent's descriptor. When the child cleans up its
   data, it will free the parent's descriptor while the parent is still
   using it.

   In the duplication function, set the child's user_event_mm to NULL
   before testing if the allocation succeeded, and when it exits it will
   not free the parent's descriptor.

 - Fix retry exhaustion in simple ring buffer reader swap

   simple_ring_buffer_swap_reader_page() starts with retry set to 8 and
   post-decrements it only after a failed link replacement. On the final
   attempt, a successful replacement leaves retry at zero, while a
   failed replacement leaves it at -1.

   But the check for success expects the retry value to be non-zero and
   exits with an error on zero. This is the opposite result. Fix it.

 - Fail nicely when the remote swap_reader_page() returns an error

   Currently, if the swap_reader_page() of a remote buffer fails, it
   triggers a WARN_ON_ONCE() and continues normally. Instead, have it
   exit with an error and a pr_warn() print instead of a full WARNING.

* tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ring-buffer: Stop remote reader update when page swap fails
  tracing: Fix retry exhaustion in simple ring buffer reader swap
  tracing/user_events: Clear copied tracing state before fork duplication
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-modify
  eventfs: Initialize ei->children and ei->list in init_ei()
  tracing: Fix use-after-free in trace_pipe read on sub-buffer order change
  tracing: Fix crash passing ERR_PTR to kthread_stop()
  tracing: Fix use-after-free with same-name named triggers
  tracing: Fix logged instance name on creation failure

6 files changed, 1414 insertions, 0 deletions

diff --git a/tools/testing/selftests/membarrier/.gitignore b/tools/testing/selftests/membarrier/.gitignore
new file mode 100644
index 000000000..f2fbba178
--- /dev/null
+++ b/tools/testing/selftests/membarrier/.gitignore
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+membarrier_test_multi_thread
+membarrier_test_single_thread
diff --git a/tools/testing/selftests/membarrier/Makefile b/tools/testing/selftests/membarrier/Makefile
new file mode 100644
index 000000000..829f95c83
--- /dev/null
+++ b/tools/testing/selftests/membarrier/Makefile
@@ -0,0 +1,9 @@
+# SPDX-License-Identifier: GPL-2.0-only
+CFLAGS += -g $(KHDR_INCLUDES) -pthread -I../../../../tools/include
+LDLIBS += -lpthread
+
+TEST_GEN_PROGS := membarrier_test_single_thread \
+		membarrier_test_multi_thread \
+		membarrier_rseq_stress
+
+include ../lib.mk
diff --git a/tools/testing/selftests/membarrier/membarrier_rseq_stress.c b/tools/testing/selftests/membarrier/membarrier_rseq_stress.c
new file mode 100644
index 000000000..c188d7498
--- /dev/null
+++ b/tools/testing/selftests/membarrier/membarrier_rseq_stress.c
@@ -0,0 +1,951 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Membarrier stress test for CFS throttle interactions.
+ *
+ * Reproducer for the interaction between CFS throttle and expedited membarrier.
+ */
+
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <pthread.h>
+#include <syscall.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <fcntl.h>
+#include <stdint.h>
+#include <errno.h>
+#include <sched.h>
+#include <time.h>
+#include <signal.h>
+#include <stdatomic.h>
+#include <dirent.h>
+#include <sys/prctl.h>
+#include <sys/mman.h>
+
+#include "../kselftest.h"
+
+/* -- Architecture-specific rseq signature -- */
+#if defined(__x86_64__) || defined(__i386__)
+# define RSEQ_SIG  0x53053053U
+#elif defined(__aarch64__)
+# define RSEQ_SIG  0xd428bc00U
+#elif defined(__powerpc__) || defined(__powerpc64__)
+# define RSEQ_SIG  0x0f000000U
+#elif defined(__s390__) || defined(__s390x__)
+# define RSEQ_SIG  0x0c000000U
+#else
+# define RSEQ_SIG  0
+# define UNSUPPORTED_ARCH 1
+#endif
+
+/* -- rseq ABI (kernel uapi; define locally for portability) -- */
+#define RSEQ_CPU_ID_UNINITIALIZED       ((__u32)-1)
+
+#include <linux/compiler.h>
+
+struct rseq_abi {
+	__u32 cpu_id_start;
+	__u32 cpu_id;
+	__u64 rseq_cs;
+	__u32 flags;
+	__u32 node_id;
+	__u32 mm_cid;
+	char  end[0];
+} __aligned(32);
+
+/* -- membarrier constants (not in all distro headers) -- */
+#ifndef MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ
+# define MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ          (1 << 7)
+#endif
+#ifndef MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ
+# define MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ (1 << 8)
+#endif
+#ifndef MEMBARRIER_CMD_FLAG_CPU
+# define MEMBARRIER_CMD_FLAG_CPU  (1 << 0)
+#endif
+
+/* -- Test parameters -- */
+#define N_SIBLINGS          2000
+#define NEST_DEPTH		5
+static char g_cgroup_path[4096];
+static int use_cgroup_v2;
+
+#define CFS_QUOTA_US        1000
+#define CFS_PERIOD_US       5000
+#define N_HAMMER_PER_CPU    25
+#define N_BURNER_PER_CPU    50
+#define MAX_STRESS_CPUS     1024
+#define TEST_DURATION_SEC   20
+
+/* Latency thresholds for the sentinel */
+#define LATENCY_WARN_MS     50
+#define LATENCY_CRITICAL_MS 200
+
+/* Sentinel sampling interval */
+#define SENTINEL_INTERVAL_US  500
+
+/* -- Shared globals -- */
+static atomic_int  g_stop;
+static atomic_int  g_stop_sentinel;
+static atomic_long g_max_latency_us;
+static atomic_long g_interval_max_latency_us;
+static atomic_long g_mb_ok;
+static atomic_long g_mb_err;
+static int         g_ncpus_stress;
+static int *g_stress_cpus;
+
+static atomic_int  g_test_ready;
+
+/* Per-thread rseq ABI block registered with the kernel */
+static __thread struct rseq_abi tls_rseq
+	__attribute__((tls_model("initial-exec"))) __aligned(32) = {
+	.cpu_id = RSEQ_CPU_ID_UNINITIALIZED,
+};
+
+/* -- Utility -- */
+static int write_file(const char *path, const char *val)
+{
+	int fd = open(path, O_WRONLY | O_CLOEXEC);
+
+	if (fd < 0)
+		return -errno;
+
+	size_t len = strlen(val);
+	ssize_t r = write(fd, val, len);
+
+	close(fd);
+	if (r < 0)
+		return -errno;
+	if ((size_t)r != len)
+		return -EIO;
+	return 0;
+}
+
+static uint64_t monotonic_us(void)
+{
+	struct timespec ts;
+
+	clock_gettime(CLOCK_MONOTONIC, &ts);
+	return (uint64_t)ts.tv_sec * 1000000ULL + ts.tv_nsec / 1000ULL;
+}
+
+static void update_max_latency(long lat)
+{
+	long old = atomic_load_explicit(&g_max_latency_us, memory_order_relaxed);
+
+	while (lat > old) {
+		if (atomic_compare_exchange_weak_explicit(&g_max_latency_us, &old, lat,
+				memory_order_relaxed, memory_order_relaxed))
+			break;
+	}
+
+	old = atomic_load_explicit(&g_interval_max_latency_us, memory_order_relaxed);
+	while (lat > old) {
+		if (atomic_compare_exchange_weak_explicit(&g_interval_max_latency_us, &old, lat,
+				memory_order_relaxed, memory_order_relaxed))
+			break;
+	}
+}
+
+static void init_stress_cpus(void)
+{
+	cpu_set_t set;
+	int capacity = MAX_STRESS_CPUS;
+
+	g_stress_cpus = malloc(capacity * sizeof(int));
+	if (!g_stress_cpus)
+		ksft_exit_fail_msg("malloc failed for g_stress_cpus\n");
+
+	if (sched_getaffinity(0, sizeof(set), &set) < 0)
+		ksft_exit_fail_msg("sched_getaffinity failed\n");
+
+	for (int i = 0; i < CPU_SETSIZE && g_ncpus_stress < capacity; i++) {
+		if (CPU_ISSET(i, &set))
+			g_stress_cpus[g_ncpus_stress++] = i;
+	}
+
+	if (g_ncpus_stress == 0)
+		ksft_exit_skip("No CPUs available for stress test\n");
+
+	ksft_print_msg("Stressing %d CPUs discovered via affinity\n", g_ncpus_stress);
+}
+
+/* -- rseq / membarrier helpers -- */
+static int rseq_register_thread(void)
+{
+	int r = syscall(SYS_rseq, &tls_rseq, sizeof(tls_rseq), 0, RSEQ_SIG);
+
+	return (r == 0 || errno == EBUSY || errno == EINVAL) ? 0 : -1;
+}
+
+static int rseq_register_thread_at(struct rseq_abi *rseq)
+{
+	int r = syscall(SYS_rseq, rseq, sizeof(*rseq), 0, RSEQ_SIG);
+
+	return (r == 0 || errno == EBUSY || errno == EINVAL) ? 0 : -1;
+}
+
+static int membarrier_register_rseq_mm(void)
+{
+	return syscall(SYS_membarrier,
+		       MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ, 0, 0);
+}
+
+/* -- cgroup helpers -- */
+static void rm_cgroup_recursive(const char *path)
+{
+	DIR *dir = opendir(path);
+
+	if (!dir)
+		return;
+	struct dirent *entry;
+
+	while ((entry = readdir(dir)) != NULL) {
+		if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
+			continue;
+		if (entry->d_type == DT_DIR) {
+			char sub_path[4096];
+
+			snprintf(sub_path, sizeof(sub_path), "%s/%s", path, entry->d_name);
+			rm_cgroup_recursive(sub_path);
+		}
+	}
+	closedir(dir);
+	rmdir(path);
+}
+
+static void cgroup_teardown(void);
+
+static int cgroup_setup(void)
+{
+	struct stat st;
+
+	if (stat("/sys/fs/cgroup/cpu", &st) == 0) {
+		use_cgroup_v2 = 0;
+		snprintf(g_cgroup_path, sizeof(g_cgroup_path),
+			 "/sys/fs/cgroup/cpu/membarrier_stress_test");
+	} else if (stat("/dev/cgroup/cpu", &st) == 0) {
+		use_cgroup_v2 = 0;
+		snprintf(g_cgroup_path, sizeof(g_cgroup_path),
+			 "/dev/cgroup/cpu/membarrier_stress_test");
+	} else if (stat("/cgroup/cpu", &st) == 0) {
+		use_cgroup_v2 = 0;
+		snprintf(g_cgroup_path, sizeof(g_cgroup_path),
+			 "/cgroup/cpu/membarrier_stress_test");
+	} else if (stat("/sys/fs/cgroup/cgroup.controllers", &st) == 0) {
+		use_cgroup_v2 = 1;
+		snprintf(g_cgroup_path, sizeof(g_cgroup_path),
+			 "/sys/fs/cgroup/membarrier_stress_test");
+	} else {
+		ksft_print_msg("WARN: cgroup mount not found. Using v2 at /sys/fs/cgroup\n");
+		use_cgroup_v2 = 1;
+		snprintf(g_cgroup_path, sizeof(g_cgroup_path),
+			 "/sys/fs/cgroup/membarrier_stress_test");
+	}
+
+	/* Robust cleanup before setup */
+	cgroup_teardown();
+
+	if (use_cgroup_v2) {
+		/* Enable cpu controller in root cgroup */
+		if (write_file("/sys/fs/cgroup/cgroup.subtree_control", "+cpu") < 0)
+			ksft_print_msg("WARN: failed to enable cpu controller in /sys/fs/cgroup\n");
+	}
+
+	if (mkdir(g_cgroup_path, 0755) < 0 && errno != EEXIST) {
+		ksft_print_msg("mkdir base %s failed: %s\n", g_cgroup_path, strerror(errno));
+		return -1;
+	}
+
+	if (use_cgroup_v2) {
+		char ctrl_path[4096];
+
+		snprintf(ctrl_path, sizeof(ctrl_path), "%s/cgroup.subtree_control", g_cgroup_path);
+		if (write_file(ctrl_path, "+cpu") < 0)
+			ksft_print_msg("WARN: failed to enable cpu controller in %s\n",
+				       g_cgroup_path);
+	}
+
+	for (int i = 0; i < N_SIBLINGS; i++) {
+		char sibling_path[4096];
+
+		snprintf(sibling_path, sizeof(sibling_path), "%s/n%d", g_cgroup_path, i);
+		if (mkdir(sibling_path, 0755) < 0 && errno != EEXIST) {
+			ksft_print_msg("mkdir wide %s failed: %s\n", sibling_path, strerror(errno));
+			return -1;
+		}
+
+		if (use_cgroup_v2) {
+			char ctrl_path[4096];
+
+			snprintf(ctrl_path, sizeof(ctrl_path),
+				 "%s/cgroup.subtree_control", sibling_path);
+			if (write_file(ctrl_path, "+cpu") < 0)
+				ksft_print_msg("WARN: failed to enable cpu controller in %s\n",
+					       sibling_path);
+		}
+
+		char current_path[4096];
+
+		snprintf(current_path, sizeof(current_path), "%s", sibling_path);
+		for (int j = 0; j < NEST_DEPTH; j++) {
+			snprintf(current_path + strlen(current_path),
+				 sizeof(current_path) - strlen(current_path), "/d%d", j);
+			if (mkdir(current_path, 0755) < 0 && errno != EEXIST) {
+				ksft_print_msg("mkdir deep %s failed: %s\n",
+					       current_path, strerror(errno));
+				return -1;
+			}
+
+			/* Enable for all but the leaf */
+			if (use_cgroup_v2 && j < NEST_DEPTH - 1) {
+				char ctrl_path[4096];
+
+				snprintf(ctrl_path, sizeof(ctrl_path), "%s/cgroup.subtree_control",
+					 current_path);
+				if (write_file(ctrl_path, "+cpu") < 0)
+					ksft_print_msg("WARN: cannot enable cpu controller in %s\n",
+						       current_path);
+			}
+		}
+	}
+
+	char quota[64], period[64], max_str[128];
+
+	snprintf(quota, sizeof(quota), "%d", CFS_QUOTA_US);
+	snprintf(period, sizeof(period), "%d", CFS_PERIOD_US);
+	snprintf(max_str, sizeof(max_str), "%d %d", CFS_QUOTA_US, CFS_PERIOD_US);
+
+	if (use_cgroup_v2) {
+		char max_path[4096];
+
+		snprintf(max_path, sizeof(max_path), "%s/cpu.max", g_cgroup_path);
+		if (write_file(max_path, max_str) < 0) {
+			ksft_print_msg("ERROR: cannot write cpu.max at %s\n", max_path);
+			return -1;
+		}
+		ksft_print_msg("cgroup (v2) %s: cpu.max=%s\n", g_cgroup_path, max_str);
+	} else {
+		char quota_path[4096], period_path[4096];
+
+		snprintf(quota_path, sizeof(quota_path), "%s/cpu.cfs_quota_us", g_cgroup_path);
+		snprintf(period_path, sizeof(period_path), "%s/cpu.cfs_period_us", g_cgroup_path);
+
+		if (write_file(period_path, period) < 0) {
+			ksft_print_msg("ERROR: cannot write cpu.cfs_period_us at %s\n",
+				       period_path);
+			return -1;
+		}
+		if (write_file(quota_path, quota) < 0) {
+			ksft_print_msg("ERROR: cannot write cpu.cfs_quota_us at %s\n", quota_path);
+			return -1;
+		}
+		ksft_print_msg("cgroup (v1) %s: cpu.cfs_quota_us=%d cpu.cfs_period_us=%d\n",
+			       g_cgroup_path, CFS_QUOTA_US, CFS_PERIOD_US);
+	}
+
+	return 0;
+}
+
+static int cgroup_add_pid_to_path(pid_t pid, const char *path)
+{
+	char buf[32], file_path[4096];
+
+	snprintf(buf, sizeof(buf), "%d", (int)pid);
+	if (use_cgroup_v2) {
+		snprintf(file_path, sizeof(file_path), "%s/cgroup.procs", path);
+		return write_file(file_path, buf);
+	}
+	/* In v1, try tasks first, fallback to cgroup.procs */
+	snprintf(file_path, sizeof(file_path), "%s/tasks", path);
+	int r = write_file(file_path, buf);
+
+	if (r < 0) {
+		snprintf(file_path, sizeof(file_path), "%s/cgroup.procs", path);
+		r = write_file(file_path, buf);
+	}
+	return r;
+}
+
+static void cgroup_teardown(void)
+{
+	rm_cgroup_recursive(g_cgroup_path);
+}
+
+static void cgroup_unthrottle(void)
+{
+	if (use_cgroup_v2) {
+		char max_path[4096];
+
+		snprintf(max_path, sizeof(max_path), "%s/cpu.max", g_cgroup_path);
+		write_file(max_path, "max");
+	} else {
+		char quota_path[4096];
+
+		snprintf(quota_path, sizeof(quota_path), "%s/cpu.cfs_quota_us", g_cgroup_path);
+		write_file(quota_path, "-1");
+	}
+}
+
+/* -- CPU burner (inside throttled child process) -- */
+static void *burner_thread_fn(void *arg)
+{
+	struct rseq_abi my_rseq;
+	int cpu = (int)(uintptr_t)arg;
+
+	memset(&my_rseq, 0, sizeof(my_rseq));
+	my_rseq.cpu_id = RSEQ_CPU_ID_UNINITIALIZED;
+
+	if (rseq_register_thread_at(&my_rseq) < 0) {
+		perror("rseq_register (burner)");
+		return NULL;
+	}
+
+	cpu_set_t set;
+
+	CPU_ZERO(&set);
+	CPU_SET(cpu, &set);
+	if (sched_setaffinity(0, sizeof(set), &set) < 0)
+		perror("sched_setaffinity (burner)");
+
+	unsigned long sink = 0;
+
+	while (!atomic_load_explicit(&g_stop, memory_order_relaxed)) {
+		sink++;
+		/* Prevent compiler from optimizing the loop away */
+		asm volatile("" : "+g"(sink));
+	}
+
+	return NULL;
+}
+
+static int burner_thread_fn_wrapper(void *arg)
+{
+	burner_thread_fn(arg);
+	return 0;
+}
+
+static int leaf_child_fn(void *arg)
+{
+	int i = (int)(uintptr_t)arg;
+	int total_burners = g_ncpus_stress * N_BURNER_PER_CPU;
+	int n_threads_per_leaf = total_burners / N_SIBLINGS;
+
+	if (i < (total_burners % N_SIBLINGS))
+		n_threads_per_leaf++;
+
+	prctl(PR_SET_PDEATHSIG, SIGTERM);
+	if (getppid() == 1)
+		_exit(1);
+
+	char leaf_path[4096];
+
+	snprintf(leaf_path, sizeof(leaf_path), "%s/n%d", g_cgroup_path, i);
+	for (int j = 0; j < NEST_DEPTH; j++)
+		snprintf(leaf_path + strlen(leaf_path),
+			 sizeof(leaf_path) - strlen(leaf_path), "/d%d", j);
+
+		int r = cgroup_add_pid_to_path(getpid(), leaf_path);
+
+		if (r < 0) {
+			char buf[512];
+			int len = snprintf(buf, sizeof(buf),
+					   "[leaf child %d] failed to join cgroup %s: err %d\n",
+					   i, leaf_path, -r);
+			(void)!write(2, buf, len);
+			_exit(1);
+		}
+
+	for (int j = 0; j < n_threads_per_leaf; j++) {
+		int cpu = g_stress_cpus[(i * n_threads_per_leaf + j) % g_ncpus_stress];
+
+		/* Allocate stack via mmap (bypasses heap) */
+		size_t stack_size = 64 * 1024;
+		void *stack = mmap(NULL, stack_size, PROT_READ | PROT_WRITE,
+				   MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+		if (stack == MAP_FAILED) {
+			const char *msg = "mmap stack failed\n";
+			(void)!write(2, msg, strlen(msg));
+			_exit(1);
+		}
+
+		/* Use raw clone to create a thread sharing the VM and thread group */
+		pid_t pid = clone(burner_thread_fn_wrapper, stack + stack_size,
+				  CLONE_VM | CLONE_THREAD | CLONE_SIGHAND,
+				  (void *)(uintptr_t)cpu);
+		if (pid < 0) {
+			const char *msg = "clone burner failed\n";
+			(void)!write(2, msg, strlen(msg));
+			_exit(1);
+		}
+	}
+
+	// Wait for SIGTERM
+	sigset_t mask;
+
+	sigemptyset(&mask);
+	sigaddset(&mask, SIGTERM);
+	int sig;
+
+	sigwait(&mask, &sig);
+
+	_exit(0);
+}
+
+struct leaf_info {
+	pid_t pid;
+	void *stack;
+};
+
+static int run_throttle_child(void *arg)
+{
+	(void)arg;
+	prctl(PR_SET_PDEATHSIG, SIGTERM);
+	if (getppid() == 1)
+		_exit(1);
+
+	int n_leafs = N_SIBLINGS;
+
+	/* Block signals before spawning to avoid missing early failures */
+	sigset_t mask;
+
+	sigemptyset(&mask);
+	sigaddset(&mask, SIGTERM);
+	sigaddset(&mask, SIGCHLD);
+	sigprocmask(SIG_BLOCK, &mask, NULL);
+
+	/* Use mmap for tracking structures to avoid glibc heap usage */
+	struct leaf_info *leaves = mmap(NULL, n_leafs * sizeof(struct leaf_info),
+					PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	if (leaves == MAP_FAILED) {
+		const char *msg = "mmap leaves array failed\n";
+		(void)!write(2, msg, strlen(msg));
+		_exit(1);
+	}
+
+	for (int i = 0; i < n_leafs; i++) {
+		size_t stack_size = 64 * 1024;
+		void *stack = mmap(NULL, stack_size, PROT_READ | PROT_WRITE,
+				   MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+		if (stack == MAP_FAILED) {
+			const char *msg = "mmap leaf stack failed\n";
+			(void)!write(2, msg, strlen(msg));
+			_exit(1);
+		}
+
+		leaves[i].stack = stack;
+
+		pid_t pid = clone(leaf_child_fn, stack + stack_size,
+				  CLONE_VM | SIGCHLD, (void *)(uintptr_t)i);
+
+		if (pid < 0) {
+			const char *msg = "clone (leaf child) failed\n";
+			(void)!write(2, msg, strlen(msg));
+
+			/* Clean up successfully spawned children */
+			for (int j = 0; j < i; j++) {
+				kill(leaves[j].pid, SIGTERM);
+				waitpid(leaves[j].pid, NULL, 0);
+				munmap(leaves[j].stack, stack_size);
+			}
+			munmap(leaves, n_leafs * sizeof(struct leaf_info));
+
+			if (errno == EAGAIN)
+				_exit(4);
+			else
+				_exit(1);
+		}
+		leaves[i].pid = pid;
+	}
+
+	int failed = 0;
+
+	while (1) {
+		int sig;
+
+		sigwait(&mask, &sig);
+
+		if (sig == SIGTERM) {
+			break;
+		} else if (sig == SIGCHLD) {
+			int status;
+			pid_t pid;
+
+			// Reap all dead children
+			while ((pid = waitpid(-1, &status, WNOHANG)) > 0) {
+				for (int i = 0; i < n_leafs; i++) {
+					if (leaves[i].pid == pid) {
+						leaves[i].pid = 0;
+						break;
+					}
+				}
+				if ((WIFEXITED(status) && WEXITSTATUS(status) != 0) ||
+				    WIFSIGNALED(status)) {
+					char buf[128];
+					int len = snprintf(buf, sizeof(buf),
+							   "[manager] child %d died unexpectedly (status %d)\n",
+							   pid, WEXITSTATUS(status));
+					(void)!write(2, buf, len);
+					failed = 1;
+				}
+			}
+			if (failed)
+				break;
+		}
+	}
+
+	// Terminate all leaf kids
+	for (int i = 0; i < n_leafs; i++) {
+		if (leaves[i].pid > 0)
+			kill(leaves[i].pid, SIGTERM);
+	}
+
+	for (int i = 0; i < n_leafs; i++) {
+		if (leaves[i].pid > 0)
+			waitpid(leaves[i].pid, NULL, 0);
+		munmap(leaves[i].stack, 64 * 1024);
+	}
+
+	munmap(leaves, n_leafs * sizeof(struct leaf_info));
+
+	_exit(failed ? 1 : 0);
+}
+
+/* -- Membarrier hammer thread -- */
+static void *hammer_thread_fn(void *arg)
+{
+	int target_cpu = *(int *)arg;
+	long local_ok = 0;
+	long local_err = 0;
+	int count = 0;
+	const int batch_size = 1024;
+
+	if (rseq_register_thread() < 0) {
+		ksft_print_msg("[hammer] rseq_register failed: %s\n", strerror(errno));
+		return NULL;
+	}
+
+	membarrier_register_rseq_mm();
+
+	while (!atomic_load_explicit(&g_stop, memory_order_relaxed)) {
+		int r = syscall(SYS_membarrier,
+				MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ,
+				MEMBARRIER_CMD_FLAG_CPU,
+				target_cpu);
+		if (__builtin_expect(r == 0, 1))
+			local_ok++;
+		else
+			local_err++;
+
+		count++;
+		if (__builtin_expect(count >= batch_size, 0)) {
+			atomic_fetch_add_explicit(&g_mb_ok, local_ok, memory_order_relaxed);
+			atomic_fetch_add_explicit(&g_mb_err, local_err, memory_order_relaxed);
+			local_ok = 0;
+			local_err = 0;
+			count = 0;
+		}
+	}
+
+	/* Flush any remaining counts on exit */
+	if (local_ok > 0)
+		atomic_fetch_add_explicit(&g_mb_ok, local_ok, memory_order_relaxed);
+	if (local_err > 0)
+		atomic_fetch_add_explicit(&g_mb_err, local_err, memory_order_relaxed);
+
+	return NULL;
+}
+
+/* -- Latency sentinel -- */
+static void *sentinel_thread_fn(void *arg)
+{
+	(void)arg;
+	struct sched_param sp = { .sched_priority = 20 };
+
+	if (sched_setscheduler(0, SCHED_FIFO, &sp) < 0)
+		ksft_print_msg("WARN: no SCHED_FIFO for sentinel (less precise)\n");
+
+	while (!atomic_load_explicit(&g_test_ready, memory_order_relaxed) &&
+	       !atomic_load_explicit(&g_stop_sentinel, memory_order_relaxed)) {
+		struct timespec ts = {0, 1000 * 1000}; /* 1ms */
+
+		clock_nanosleep(CLOCK_MONOTONIC, 0, &ts, NULL);
+	}
+
+	uint64_t prev = monotonic_us();
+
+	while (!atomic_load_explicit(&g_stop_sentinel, memory_order_relaxed)) {
+		struct timespec ts = {
+			.tv_sec  = 0,
+			.tv_nsec = SENTINEL_INTERVAL_US * 1000L,
+		};
+		clock_nanosleep(CLOCK_MONOTONIC, 0, &ts, NULL);
+
+		uint64_t now = monotonic_us();
+		long latency_us = (long)(now - prev) - SENTINEL_INTERVAL_US;
+
+		prev = now;
+
+		if (latency_us <= 0)
+			continue;
+
+		update_max_latency(latency_us);
+
+		if (latency_us > LATENCY_CRITICAL_MS * 1000L) {
+			ksft_print_msg("\n[SENTINEL] CRITICAL: %ld ms delay (lockup precursor!)\n",
+				latency_us / 1000);
+		} else if (latency_us > LATENCY_WARN_MS * 1000L) {
+			ksft_print_msg("\n[SENTINEL] WARN: %ld ms latency spike\n",
+				latency_us / 1000);
+		}
+	}
+	return NULL;
+}
+
+/* -- Progress reporter -- */
+static void *reporter_thread_fn(void *arg)
+{
+	(void)arg;
+	int elapsed = 0;
+
+	while (!atomic_load_explicit(&g_stop_sentinel, memory_order_relaxed)) {
+		for (int i = 0; i < 5; i++) {
+			sleep(1);
+			if (atomic_load_explicit(&g_stop_sentinel, memory_order_relaxed))
+				break;
+		}
+		if (atomic_load_explicit(&g_stop_sentinel, memory_order_relaxed))
+			break;
+		elapsed += 5;
+		long interval_max = atomic_exchange_explicit(&g_interval_max_latency_us,
+							     0, memory_order_relaxed);
+
+		ksft_print_msg("[%3ds] mb: ok=%-10ld err=%-8ld | max_lat=%ld us\n",
+		       elapsed,
+		       atomic_load(&g_mb_ok),
+		       atomic_load(&g_mb_err),
+		       interval_max);
+	}
+	return NULL;
+}
+
+/* -- Main -- */
+int main(void)
+{
+	ksft_print_header();
+#ifdef UNSUPPORTED_ARCH
+	ksft_exit_skip("Unsupported architecture\n");
+#endif
+	ksft_set_plan(1);
+
+	if (geteuid() != 0)
+		ksft_exit_skip("Must run as root (cgroup + SCHED_FIFO)\n");
+
+	init_stress_cpus();
+
+	ksft_print_msg("=== membarrier rseq + CFS unthrottle stress ===\n");
+	ksft_print_msg("Stressing CPUs: %d\n", g_ncpus_stress);
+	ksft_print_msg("Quota: %d/%d us  (~%d unthrottles/sec/CPU)\n",
+	       CFS_QUOTA_US, CFS_PERIOD_US,
+	       1000000 / CFS_PERIOD_US);
+	ksft_print_msg("Hammer threads: %d per CPU (%d total)\n",
+	       N_HAMMER_PER_CPU, g_ncpus_stress * N_HAMMER_PER_CPU);
+	ksft_print_msg("Duration: %d seconds\n\n", TEST_DURATION_SEC);
+
+	if (cgroup_setup() < 0) {
+		cgroup_teardown();
+		ksft_exit_skip("cgroup_setup failed (missing permissions or v2 ctrls?)\n");
+	}
+
+	if (rseq_register_thread() < 0) {
+		ksft_print_msg("rseq_register (%s) failed: %s\n", __func__, strerror(errno));
+		cgroup_teardown();
+		ksft_exit_skip("rseq syscall failed or not available\n");
+	}
+	if (membarrier_register_rseq_mm() < 0) {
+		ksft_print_msg("MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ: %s\n"
+			"Kernel >= 5.10 with CONFIG_RSEQ required.\n",
+			strerror(errno));
+		cgroup_teardown();
+		ksft_exit_skip("membarrier register failed\n");
+	}
+	ksft_print_msg("rseq membarrier registered OK\n");
+
+	sigset_t sigmask;
+
+	sigemptyset(&sigmask);
+	sigaddset(&sigmask, SIGTERM);
+	sigprocmask(SIG_BLOCK, &sigmask, NULL);
+
+	void *stack = malloc(1024 * 1024);
+
+	if (!stack) {
+		perror("malloc stack");
+		cgroup_teardown();
+		ksft_exit_fail_msg("Malloc stack failed\n");
+	}
+	pid_t child = clone(run_throttle_child, stack + 1024 * 1024, CLONE_VM | SIGCHLD, NULL);
+
+	if (child < 0) {
+		perror("clone");
+		cgroup_teardown();
+		ksft_exit_fail_msg("Clone failed\n");
+	}
+
+	sigprocmask(SIG_UNBLOCK, &sigmask, NULL);
+	ksft_print_msg("Throttle child PID %d started\n", child);
+
+	int n_threads = g_ncpus_stress * N_HAMMER_PER_CPU + 2;
+	pthread_t *threads = (pthread_t *)calloc(n_threads, sizeof(pthread_t));
+	int       *cpuargs = (int *)calloc(g_ncpus_stress * N_HAMMER_PER_CPU, sizeof(int));
+
+	if (!threads || !cpuargs) {
+		perror("calloc");
+		kill(child, SIGTERM);
+		waitpid(child, NULL, 0);
+		cgroup_teardown();
+		ksft_exit_fail_msg("Thread allocation failed\n");
+	}
+
+	int ti = 0, ai = 0;
+	int r;
+
+	ksft_print_msg("Creating sentinel thread...\n");
+	r = pthread_create(&threads[ti], NULL, sentinel_thread_fn, NULL);
+	if (r != 0) {
+		kill(child, SIGTERM);
+		waitpid(child, NULL, 0);
+		cgroup_teardown();
+		free(threads);
+		free(cpuargs);
+		free(g_stress_cpus);
+		ksft_exit_fail_msg("pthread_create (sentinel) failed: %s\n", strerror(r));
+	}
+	ti++;
+
+	ksft_print_msg("Creating reporter thread...\n");
+	r = pthread_create(&threads[ti], NULL, reporter_thread_fn, NULL);
+	if (r != 0) {
+		atomic_store(&g_stop_sentinel, 1);
+		pthread_join(threads[0], NULL);
+		kill(child, SIGTERM);
+		waitpid(child, NULL, 0);
+		cgroup_teardown();
+		free(threads);
+		free(cpuargs);
+		free(g_stress_cpus);
+		ksft_exit_fail_msg("pthread_create (reporter) failed: %s\n", strerror(r));
+	}
+	ti++;
+
+	ksft_print_msg("Creating %d hammer threads...\n", g_ncpus_stress * N_HAMMER_PER_CPU);
+	for (int i = 0; i < g_ncpus_stress; i++) {
+		int cpu = g_stress_cpus[i];
+
+		for (int j = 0; j < N_HAMMER_PER_CPU; j++) {
+			cpuargs[ai] = cpu;
+			r = pthread_create(&threads[ti], NULL, hammer_thread_fn, &cpuargs[ai]);
+			if (r != 0) {
+				ksft_print_msg("pthread_create failed at thread %d: %s\n",
+					       ti, strerror(r));
+
+				atomic_store(&g_stop_sentinel, 1);
+				pthread_join(threads[0], NULL);
+				pthread_join(threads[1], NULL);
+
+				atomic_store(&g_stop, 1);
+				for (int k = 2; k < ti; k++)
+					pthread_join(threads[k], NULL);
+
+				kill(child, SIGTERM);
+				waitpid(child, NULL, 0);
+				cgroup_teardown();
+
+				free(threads);
+				free(cpuargs);
+				free(g_stress_cpus);
+
+				if (r == EAGAIN)
+					ksft_exit_skip("Resource limits prevent threads\n");
+				else
+					ksft_exit_fail_msg("Failed to create hammer thread\n");
+			}
+			ti++;
+			ai++;
+		}
+	}
+
+	ksft_print_msg("All threads running. Tip: monitor dmesg for lockups\n\n");
+
+	atomic_store_explicit(&g_test_ready, 1, memory_order_relaxed);
+	int child_failed = 0;
+	int child_status = 0;
+
+	for (int i = 0; i < TEST_DURATION_SEC; i++) {
+		sleep(1);
+		int r = waitpid(child, &child_status, WNOHANG);
+
+		if (r == child) {
+			child_failed = 1;
+			break;
+		}
+	}
+
+	atomic_store(&g_stop_sentinel, 1);
+	pthread_join(threads[0], NULL);
+	pthread_join(threads[1], NULL);
+
+	atomic_store(&g_stop, 1);
+
+	/* Unthrottle to allow children to exit quickly */
+	cgroup_unthrottle();
+
+	if (!child_failed) {
+		kill(child, SIGTERM);
+		waitpid(child, NULL, 0);
+	}
+	for (int i = 2; i < ti; i++)
+		pthread_join(threads[i], NULL);
+
+	long max_lat   = atomic_load(&g_max_latency_us);
+	long total_ok  = atomic_load(&g_mb_ok);
+	long total_err = atomic_load(&g_mb_err);
+
+	ksft_print_msg("\n=== RESULTS ===\n");
+	ksft_print_msg("membarrier syscalls : %ld ok  %ld errors\n", total_ok, total_err);
+	ksft_print_msg("Max scheduler latency: %ld us  (%ld ms)\n", max_lat, max_lat / 1000);
+	cgroup_teardown();
+	free(threads);
+	free(cpuargs);
+	free(g_stress_cpus);
+
+	if (child_failed) {
+		if (WIFEXITED(child_status) && WEXITSTATUS(child_status) == 4)
+			ksft_exit_skip("Manager child skipped (resource limits?)\n");
+		ksft_test_result_fail("membarrier_rseq_stress: Manager child died early\n");
+		ksft_exit_fail();
+	} else if (total_ok == 0) {
+		ksft_test_result_fail("membarrier_rseq_stress: No successful membarrier calls\n");
+		ksft_exit_fail();
+	} else if (total_err > 0) {
+		ksft_test_result_fail("membarrier_rseq_stress: syscall errors\n");
+		ksft_exit_fail();
+	} else if (max_lat > LATENCY_CRITICAL_MS * 1000L) {
+		ksft_test_result_fail("membarrier_rseq_stress: LOCKUP PRECURSOR\n");
+		ksft_exit_fail();
+	} else if (max_lat > LATENCY_WARN_MS * 1000L) {
+		ksft_test_result_fail("membarrier_rseq_stress: significant latency spike\n");
+		ksft_exit_fail();
+	} else {
+		ksft_test_result_pass("membarrier_rseq_stress\n");
+		ksft_exit_pass();
+	}
+
+	return 0;
+}
diff --git a/tools/testing/selftests/membarrier/membarrier_test_impl.h b/tools/testing/selftests/membarrier/membarrier_test_impl.h
new file mode 100644
index 000000000..f6d7c44b2
--- /dev/null
+++ b/tools/testing/selftests/membarrier/membarrier_test_impl.h
@@ -0,0 +1,350 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#define _GNU_SOURCE
+#include <linux/membarrier.h>
+#include <syscall.h>
+#include <stdio.h>
+#include <errno.h>
+#include <string.h>
+#include <pthread.h>
+
+#include "kselftest.h"
+
+static int registrations;
+
+static int sys_membarrier(int cmd, int flags)
+{
+	return syscall(__NR_membarrier, cmd, flags);
+}
+
+static int test_membarrier_get_registrations(int cmd)
+{
+	int ret, flags = 0;
+	const char *test_name =
+		"sys membarrier MEMBARRIER_CMD_GET_REGISTRATIONS";
+
+	registrations |= cmd;
+
+	ret = sys_membarrier(MEMBARRIER_CMD_GET_REGISTRATIONS, 0);
+	if (ret < 0) {
+		ksft_exit_fail_msg(
+			"%s test: flags = %d, errno = %d\n",
+			test_name, flags, errno);
+	} else if (ret != registrations) {
+		ksft_exit_fail_msg(
+			"%s test: flags = %d, ret = %d, registrations = %d\n",
+			test_name, flags, ret, registrations);
+	}
+	ksft_test_result_pass(
+		"%s test: flags = %d, ret = %d, registrations = %d\n",
+		test_name, flags, ret, registrations);
+
+	return 0;
+}
+
+static int test_membarrier_cmd_fail(void)
+{
+	int cmd = -1, flags = 0;
+	const char *test_name = "sys membarrier invalid command";
+
+	if (sys_membarrier(cmd, flags) != -1) {
+		ksft_exit_fail_msg(
+			"%s test: command = %d, flags = %d. Should fail, but passed\n",
+			test_name, cmd, flags);
+	}
+	if (errno != EINVAL) {
+		ksft_exit_fail_msg(
+			"%s test: flags = %d. Should return (%d: \"%s\"), but returned (%d: \"%s\").\n",
+			test_name, flags, EINVAL, strerror(EINVAL),
+			errno, strerror(errno));
+	}
+
+	ksft_test_result_pass(
+		"%s test: command = %d, flags = %d, errno = %d. Failed as expected\n",
+		test_name, cmd, flags, errno);
+	return 0;
+}
+
+static int test_membarrier_flags_fail(void)
+{
+	int cmd = MEMBARRIER_CMD_QUERY, flags = 1;
+	const char *test_name = "sys membarrier MEMBARRIER_CMD_QUERY invalid flags";
+
+	if (sys_membarrier(cmd, flags) != -1) {
+		ksft_exit_fail_msg(
+			"%s test: flags = %d. Should fail, but passed\n",
+			test_name, flags);
+	}
+	if (errno != EINVAL) {
+		ksft_exit_fail_msg(
+			"%s test: flags = %d. Should return (%d: \"%s\"), but returned (%d: \"%s\").\n",
+			test_name, flags, EINVAL, strerror(EINVAL),
+			errno, strerror(errno));
+	}
+
+	ksft_test_result_pass(
+		"%s test: flags = %d, errno = %d. Failed as expected\n",
+		test_name, flags, errno);
+	return 0;
+}
+
+static int test_membarrier_global_success(void)
+{
+	int cmd = MEMBARRIER_CMD_GLOBAL, flags = 0;
+	const char *test_name = "sys membarrier MEMBARRIER_CMD_GLOBAL";
+
+	if (sys_membarrier(cmd, flags) != 0) {
+		ksft_exit_fail_msg(
+			"%s test: flags = %d, errno = %d\n",
+			test_name, flags, errno);
+	}
+
+	ksft_test_result_pass(
+		"%s test: flags = %d\n", test_name, flags);
+	return 0;
+}
+
+static int test_membarrier_private_expedited_fail(void)
+{
+	int cmd = MEMBARRIER_CMD_PRIVATE_EXPEDITED, flags = 0;
+	const char *test_name = "sys membarrier MEMBARRIER_CMD_PRIVATE_EXPEDITED not registered failure";
+
+	if (sys_membarrier(cmd, flags) != -1) {
+		ksft_exit_fail_msg(
+			"%s test: flags = %d. Should fail, but passed\n",
+			test_name, flags);
+	}
+	if (errno != EPERM) {
+		ksft_exit_fail_msg(
+			"%s test: flags = %d. Should return (%d: \"%s\"), but returned (%d: \"%s\").\n",
+			test_name, flags, EPERM, strerror(EPERM),
+			errno, strerror(errno));
+	}
+
+	ksft_test_result_pass(
+		"%s test: flags = %d, errno = %d\n",
+		test_name, flags, errno);
+	return 0;
+}
+
+static int test_membarrier_register_private_expedited_success(void)
+{
+	int cmd = MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED, flags = 0;
+	const char *test_name = "sys membarrier MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED";
+
+	if (sys_membarrier(cmd, flags) != 0) {
+		ksft_exit_fail_msg(
+			"%s test: flags = %d, errno = %d\n",
+			test_name, flags, errno);
+	}
+
+	ksft_test_result_pass(
+		"%s test: flags = %d\n",
+		test_name, flags);
+
+	test_membarrier_get_registrations(cmd);
+	return 0;
+}
+
+static int test_membarrier_private_expedited_success(void)
+{
+	int cmd = MEMBARRIER_CMD_PRIVATE_EXPEDITED, flags = 0;
+	const char *test_name = "sys membarrier MEMBARRIER_CMD_PRIVATE_EXPEDITED";
+
+	if (sys_membarrier(cmd, flags) != 0) {
+		ksft_exit_fail_msg(
+			"%s test: flags = %d, errno = %d\n",
+			test_name, flags, errno);
+	}
+
+	ksft_test_result_pass(
+		"%s test: flags = %d\n",
+		test_name, flags);
+	return 0;
+}
+
+static int test_membarrier_private_expedited_sync_core_fail(void)
+{
+	int cmd = MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE, flags = 0;
+	const char *test_name = "sys membarrier MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE not registered failure";
+
+	if (sys_membarrier(cmd, flags) != -1) {
+		ksft_exit_fail_msg(
+			"%s test: flags = %d. Should fail, but passed\n",
+			test_name, flags);
+	}
+	if (errno != EPERM) {
+		ksft_exit_fail_msg(
+			"%s test: flags = %d. Should return (%d: \"%s\"), but returned (%d: \"%s\").\n",
+			test_name, flags, EPERM, strerror(EPERM),
+			errno, strerror(errno));
+	}
+
+	ksft_test_result_pass(
+		"%s test: flags = %d, errno = %d\n",
+		test_name, flags, errno);
+	return 0;
+}
+
+static int test_membarrier_register_private_expedited_sync_core_success(void)
+{
+	int cmd = MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE, flags = 0;
+	const char *test_name = "sys membarrier MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE";
+
+	if (sys_membarrier(cmd, flags) != 0) {
+		ksft_exit_fail_msg(
+			"%s test: flags = %d, errno = %d\n",
+			test_name, flags, errno);
+	}
+
+	ksft_test_result_pass(
+		"%s test: flags = %d\n",
+		test_name, flags);
+
+	test_membarrier_get_registrations(cmd);
+	return 0;
+}
+
+static int test_membarrier_private_expedited_sync_core_success(void)
+{
+	int cmd = MEMBARRIER_CMD_PRIVATE_EXPEDITED, flags = 0;
+	const char *test_name = "sys membarrier MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE";
+
+	if (sys_membarrier(cmd, flags) != 0) {
+		ksft_exit_fail_msg(
+			"%s test: flags = %d, errno = %d\n",
+			test_name, flags, errno);
+	}
+
+	ksft_test_result_pass(
+		"%s test: flags = %d\n",
+		test_name, flags);
+	return 0;
+}
+
+static int test_membarrier_register_global_expedited_success(void)
+{
+	int cmd = MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED, flags = 0;
+	const char *test_name = "sys membarrier MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED";
+
+	if (sys_membarrier(cmd, flags) != 0) {
+		ksft_exit_fail_msg(
+			"%s test: flags = %d, errno = %d\n",
+			test_name, flags, errno);
+	}
+
+	ksft_test_result_pass(
+		"%s test: flags = %d\n",
+		test_name, flags);
+
+	test_membarrier_get_registrations(cmd);
+	return 0;
+}
+
+static int test_membarrier_global_expedited_success(void)
+{
+	int cmd = MEMBARRIER_CMD_GLOBAL_EXPEDITED, flags = 0;
+	const char *test_name = "sys membarrier MEMBARRIER_CMD_GLOBAL_EXPEDITED";
+
+	if (sys_membarrier(cmd, flags) != 0) {
+		ksft_exit_fail_msg(
+			"%s test: flags = %d, errno = %d\n",
+			test_name, flags, errno);
+	}
+
+	ksft_test_result_pass(
+		"%s test: flags = %d\n",
+		test_name, flags);
+	return 0;
+}
+
+static int test_membarrier_fail(void)
+{
+	int status;
+
+	status = test_membarrier_cmd_fail();
+	if (status)
+		return status;
+	status = test_membarrier_flags_fail();
+	if (status)
+		return status;
+	status = test_membarrier_private_expedited_fail();
+	if (status)
+		return status;
+	status = sys_membarrier(MEMBARRIER_CMD_QUERY, 0);
+	if (status < 0) {
+		ksft_test_result_fail("sys_membarrier() failed\n");
+		return status;
+	}
+	if (status & MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE) {
+		status = test_membarrier_private_expedited_sync_core_fail();
+		if (status)
+			return status;
+	}
+	return 0;
+}
+
+static int test_membarrier_success(void)
+{
+	int status;
+
+	status = test_membarrier_global_success();
+	if (status)
+		return status;
+	status = test_membarrier_register_private_expedited_success();
+	if (status)
+		return status;
+	status = test_membarrier_private_expedited_success();
+	if (status)
+		return status;
+	status = sys_membarrier(MEMBARRIER_CMD_QUERY, 0);
+	if (status < 0) {
+		ksft_test_result_fail("sys_membarrier() failed\n");
+		return status;
+	}
+	if (status & MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE) {
+		status = test_membarrier_register_private_expedited_sync_core_success();
+		if (status)
+			return status;
+		status = test_membarrier_private_expedited_sync_core_success();
+		if (status)
+			return status;
+	}
+	/*
+	 * It is valid to send a global membarrier from a non-registered
+	 * process.
+	 */
+	status = test_membarrier_global_expedited_success();
+	if (status)
+		return status;
+	status = test_membarrier_register_global_expedited_success();
+	if (status)
+		return status;
+	status = test_membarrier_global_expedited_success();
+	if (status)
+		return status;
+	return 0;
+}
+
+static int test_membarrier_query(void)
+{
+	int flags = 0, ret;
+
+	ret = sys_membarrier(MEMBARRIER_CMD_QUERY, flags);
+	if (ret < 0) {
+		if (errno == ENOSYS) {
+			/*
+			 * It is valid to build a kernel with
+			 * CONFIG_MEMBARRIER=n. However, this skips the tests.
+			 */
+			ksft_exit_skip(
+				"sys membarrier (CONFIG_MEMBARRIER) is disabled.\n");
+		}
+		ksft_exit_fail_msg("sys_membarrier() failed\n");
+	}
+	if (!(ret & MEMBARRIER_CMD_GLOBAL))
+		ksft_exit_skip(
+			"sys_membarrier unsupported: CMD_GLOBAL not found.\n");
+
+	ksft_test_result_pass("sys_membarrier available\n");
+	return 0;
+}
diff --git a/tools/testing/selftests/membarrier/membarrier_test_multi_thread.c b/tools/testing/selftests/membarrier/membarrier_test_multi_thread.c
new file mode 100644
index 000000000..4e14dba81
--- /dev/null
+++ b/tools/testing/selftests/membarrier/membarrier_test_multi_thread.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+#include <linux/membarrier.h>
+#include <syscall.h>
+#include <stdio.h>
+#include <errno.h>
+#include <string.h>
+#include <pthread.h>
+
+#include "membarrier_test_impl.h"
+
+static int thread_ready, thread_quit;
+static pthread_mutex_t test_membarrier_thread_mutex =
+	PTHREAD_MUTEX_INITIALIZER;
+static pthread_cond_t test_membarrier_thread_cond =
+	PTHREAD_COND_INITIALIZER;
+
+void *test_membarrier_thread(void *arg)
+{
+	pthread_mutex_lock(&test_membarrier_thread_mutex);
+	thread_ready = 1;
+	pthread_cond_broadcast(&test_membarrier_thread_cond);
+	pthread_mutex_unlock(&test_membarrier_thread_mutex);
+
+	pthread_mutex_lock(&test_membarrier_thread_mutex);
+	while (!thread_quit)
+		pthread_cond_wait(&test_membarrier_thread_cond,
+				  &test_membarrier_thread_mutex);
+	pthread_mutex_unlock(&test_membarrier_thread_mutex);
+
+	return NULL;
+}
+
+static int test_mt_membarrier(void)
+{
+	int i;
+	pthread_t test_thread;
+
+	pthread_create(&test_thread, NULL,
+		       test_membarrier_thread, NULL);
+
+	pthread_mutex_lock(&test_membarrier_thread_mutex);
+	while (!thread_ready)
+		pthread_cond_wait(&test_membarrier_thread_cond,
+				  &test_membarrier_thread_mutex);
+	pthread_mutex_unlock(&test_membarrier_thread_mutex);
+
+	test_membarrier_fail();
+
+	test_membarrier_success();
+
+	pthread_mutex_lock(&test_membarrier_thread_mutex);
+	thread_quit = 1;
+	pthread_cond_broadcast(&test_membarrier_thread_cond);
+	pthread_mutex_unlock(&test_membarrier_thread_mutex);
+
+	pthread_join(test_thread, NULL);
+
+	return 0;
+}
+
+int main(int argc, char **argv)
+{
+	ksft_print_header();
+	ksft_set_plan(16);
+
+	test_membarrier_query();
+
+	/* Multi-threaded */
+	test_mt_membarrier();
+
+	ksft_exit_pass();
+}
diff --git a/tools/testing/selftests/membarrier/membarrier_test_single_thread.c b/tools/testing/selftests/membarrier/membarrier_test_single_thread.c
new file mode 100644
index 000000000..fa3f1d6c3
--- /dev/null
+++ b/tools/testing/selftests/membarrier/membarrier_test_single_thread.c
@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+#include <linux/membarrier.h>
+#include <syscall.h>
+#include <stdio.h>
+#include <errno.h>
+#include <string.h>
+#include <pthread.h>
+
+#include "membarrier_test_impl.h"
+
+int main(int argc, char **argv)
+{
+	ksft_print_header();
+	ksft_set_plan(18);
+
+	test_membarrier_get_registrations(/*cmd=*/0);
+
+	test_membarrier_query();
+
+	test_membarrier_fail();
+
+	test_membarrier_success();
+
+	test_membarrier_get_registrations(/*cmd=*/0);
+
+	ksft_exit_pass();
+}