[PATCH RFC 1/4] torture: Add a hazptrtorture.c torture test

["Paul E. McKenney" <paulmck@kernel.org>]

This commit adds a torture test for hazard pointers.

[ paulmck: Apply kernel test robot feedback. ]

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 include/linux/torture.h                       |   2 +-
 kernel/rcu/Kconfig.debug                      |  12 +
 kernel/rcu/Makefile                           |   1 +
 kernel/rcu/hazptrtorture.c                    | 684 ++++++++++++++++++
 kernel/rcu/update.c                           |   3 +-
 tools/testing/selftests/rcutorture/bin/kvm.sh |   6 +-
 .../rcutorture/configs/hazptr/CFLIST          |   2 +
 .../rcutorture/configs/hazptr/CFcommon        |   2 +
 .../rcutorture/configs/hazptr/NOPREEMPT       |  17 +
 .../rcutorture/configs/hazptr/PREEMPT         |  14 +
 .../configs/hazptr/ver_functions.sh           |  40 +
 11 files changed, 778 insertions(+), 5 deletions(-)
 create mode 100644 kernel/rcu/hazptrtorture.c
 create mode 100644 tools/testing/selftests/rcutorture/configs/hazptr/CFLIST
 create mode 100644 tools/testing/selftests/rcutorture/configs/hazptr/CFcommon
 create mode 100644 tools/testing/selftests/rcutorture/configs/hazptr/NOPREEMPT
 create mode 100644 tools/testing/selftests/rcutorture/configs/hazptr/PREEMPT
 create mode 100644 tools/testing/selftests/rcutorture/configs/hazptr/ver_functions.sh

diff --git a/include/linux/torture.h b/include/linux/torture.h
index 1b59056c3b1822..d80f24ff69e3e1 100644
--- a/include/linux/torture.h
+++ b/include/linux/torture.h
@@ -130,7 +130,7 @@ void _torture_stop_kthread(char *m, struct task_struct **tp);
 #define torture_preempt_schedule()	do { } while (0)
 #endif
 
-#if IS_ENABLED(CONFIG_RCU_TORTURE_TEST) || IS_MODULE(CONFIG_RCU_TORTURE_TEST) || IS_ENABLED(CONFIG_LOCK_TORTURE_TEST) || IS_MODULE(CONFIG_LOCK_TORTURE_TEST)
+#if IS_ENABLED(CONFIG_RCU_TORTURE_TEST) || IS_ENABLED(CONFIG_LOCK_TORTURE_TEST) || IS_ENABLED(CONFIG_HAZPTR_TORTURE_TEST)
 long torture_sched_setaffinity(pid_t pid, const struct cpumask *in_mask, bool dowarn);
 #endif
 
diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
index 83ac4e82cad7ee..7629c345b0b68f 100644
--- a/kernel/rcu/Kconfig.debug
+++ b/kernel/rcu/Kconfig.debug
@@ -113,6 +113,18 @@ config RCU_REF_SCALE_TEST
 	  Say M if you want to build it as a module instead.
 	  Say N if you are unsure.
 
+config HAZPTR_TORTURE_TEST
+	tristate "Torture tests for hazard pointers"
+	depends on DEBUG_KERNEL
+	select TORTURE_TEST
+	default n
+	help
+	  This option provides in-kernel hazard-pointer stress tests.
+
+	  Say Y here if you want hazard-pointer testing built into the kernel.
+	  Say M if you want to build them as a module instead.
+	  Say N if you are unsure.
+
 config REPRO_TEST
 	tristate "Bug-reproducibility kernel code"
 	depends on DEBUG_KERNEL
diff --git a/kernel/rcu/Makefile b/kernel/rcu/Makefile
index c97351ec679adc..12bddae9dd266e 100644
--- a/kernel/rcu/Makefile
+++ b/kernel/rcu/Makefile
@@ -10,6 +10,7 @@ endif
 obj-y += update.o sync.o
 obj-$(CONFIG_TREE_SRCU) += srcutree.o
 obj-$(CONFIG_TINY_SRCU) += srcutiny.o
+obj-$(CONFIG_HAZPTR_TORTURE_TEST) += hazptrtorture.o
 obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
 obj-$(CONFIG_RCU_SCALE_TEST) += rcuscale.o
 obj-$(CONFIG_RCU_REF_SCALE_TEST) += refscale.o
diff --git a/kernel/rcu/hazptrtorture.c b/kernel/rcu/hazptrtorture.c
new file mode 100644
index 00000000000000..1949a8da4f8c9d
--- /dev/null
+++ b/kernel/rcu/hazptrtorture.c
@@ -0,0 +1,684 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Hazard-pointer module-based torture test facility
+ *
+ * Copyright (c) 2026 Meta Platforms, Inc. and affiliates.
+ *
+ * Author: Paul E. McKenney <paulmck@kernel.org>
+ */
+
+#define pr_fmt(fmt) fmt
+
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/sched/debug.h>
+#include <linux/delay.h>
+#include <linux/kthread.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/reboot.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/torture.h>
+#include <linux/hazptr.h>
+#include <linux/rcupdate.h>
+
+#include "rcu.h"
+
+MODULE_DESCRIPTION("Hazard-pointer module-based torture test facility");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Paul E. McKenney <paulmckrcu@meta.com>");
+
+torture_param(int, irqreader, 1, "Allow hazard-pointer readers from irq handlers");
+// @@@ torture_param(int, leakpointer, 0, "Leak pointer dereferences from readers");
+torture_param(int, nreaders, -1, "Number of hazard-pointer reader threads");
+torture_param(int, onoff_holdoff, 0, "Time after boot before CPU hotplugs (s)");
+torture_param(int, onoff_interval, 0, "Time between CPU hotplugs (jiffies), 0=disable");
+// @@@ Move the rcu_torture_preempt() function and friends to kernel/torture.c.
+torture_param(int, preempt_duration, 0, "Preemption duration (ms), zero to disable");
+torture_param(int, preempt_interval, MSEC_PER_SEC, "Interval between preemptions (ms)");
+torture_param(int, shuffle_interval, 3, "Number of seconds between shuffles");
+torture_param(int, shutdown_secs, 0, "Shutdown time (s), <= zero to disable.");
+torture_param(int, stat_interval, 60, "Number of seconds between stats printk()s");
+torture_param(int, stutter, 5, "Number of seconds to run/halt test");
+torture_param(int, verbose, 1, "Enable verbose debugging printk()s");
+
+static char *torture_type = "hazptr";
+module_param(torture_type, charp, 0444);
+MODULE_PARM_DESC(torture_type, "Type of hazard pointers to torture (hazptr, ...)");
+
+static int nrealreaders;
+static struct task_struct *writer_task;
+static struct task_struct *preempt_task;
+static struct task_struct **reader_tasks;
+static struct task_struct *stats_task;
+
+#define HAZPTR_TORTURE_PIPE_LEN 10
+
+// Update-side data structure used to check RCU readers.
+struct hazptr_torture {
+	void *obj_hazptr;
+	int htort_pipe_count;
+	struct list_head htort_free;
+};
+
+static LIST_HEAD(hazptr_torture_freelist);
+static struct hazptr_torture /* __hazptr @@@ */ *hazptr_torture_current;
+static unsigned long hazptr_torture_current_version;
+static struct hazptr_torture hazptr_tortures[10 * HAZPTR_TORTURE_PIPE_LEN];
+static DEFINE_SPINLOCK(hazptr_torture_lock);
+static DEFINE_PER_CPU(long [HAZPTR_TORTURE_PIPE_LEN + 1], hazptr_torture_count);
+static atomic_t hazptr_torture_wcount[HAZPTR_TORTURE_PIPE_LEN + 1];
+static atomic_t n_hazptr_torture_alloc;
+static atomic_t n_hazptr_torture_alloc_fail;
+static atomic_t n_hazptr_torture_free;
+static atomic_t n_hazptr_torture_error;
+static struct list_head hazptr_torture_removed;
+
+/* @@@ */ static int hazptr_torture_writer_state;
+#define HTWS_FIXED_DELAY	0
+#define HTWS_DELAY		1
+#define HTWS_REPLACE		2
+#define HTWS_SYNC		3
+#define HTWS_STUTTER		4
+#define HTWS_STOPPING		5
+static const char * const hazptr_torture_writer_state_names[] = {
+	"HTWS_FIXED_DELAY",
+	"HTWS_DELAY",
+	"HTWS_REPLACE",
+	"HTWS_SYNC",
+	"HTWS_STUTTER",
+	"HTWS_STOPPING",
+};
+
+static const char *hazptr_torture_writer_state_getname(void)
+{
+	unsigned int i = READ_ONCE(hazptr_torture_writer_state);
+
+	if (i >= ARRAY_SIZE(hazptr_torture_writer_state_names))
+		return "???";
+	return hazptr_torture_writer_state_names[i];
+}
+
+/*
+ * Allocate an element from the hazptr_tortures pool.
+ */
+static struct hazptr_torture *hazptr_torture_alloc(void)
+{
+	struct list_head *p;
+
+	spin_lock_bh(&hazptr_torture_lock);
+	if (list_empty(&hazptr_torture_freelist)) {
+		atomic_inc(&n_hazptr_torture_alloc_fail);
+		spin_unlock_bh(&hazptr_torture_lock);
+		return NULL;
+	}
+	atomic_inc(&n_hazptr_torture_alloc);
+	p = hazptr_torture_freelist.next;
+	list_del_init(p);
+	spin_unlock_bh(&hazptr_torture_lock);
+	return container_of(p, struct hazptr_torture, htort_free);
+}
+
+/*
+ * Free an element to the hazptr_tortures pool.
+ */
+static void
+hazptr_torture_free(struct hazptr_torture *p)
+{
+	atomic_inc(&n_hazptr_torture_free);
+	spin_lock_bh(&hazptr_torture_lock);
+	list_add_tail(&p->htort_free, &hazptr_torture_freelist);
+	spin_unlock_bh(&hazptr_torture_lock);
+}
+
+/*
+ * Update object in the pipe.  This should be invoked after a suitable time.
+ */
+static bool
+hazptr_torture_pipe_update_one(struct hazptr_torture *rp)
+{
+	int i;
+
+	i = rp->htort_pipe_count;
+	if (i > HAZPTR_TORTURE_PIPE_LEN)
+		i = HAZPTR_TORTURE_PIPE_LEN;
+	atomic_inc(&hazptr_torture_wcount[i]);
+	WRITE_ONCE(rp->htort_pipe_count, i + 1);
+	ASSERT_EXCLUSIVE_WRITER(rp->htort_pipe_count);
+	if (i + 1 >= HAZPTR_TORTURE_PIPE_LEN)
+		return true;
+	return false;
+}
+
+/*
+ * Update all callbacks in the pipe each time period.
+ */
+static void
+hazptr_torture_pipe_update(struct hazptr_torture *old_rp)
+{
+	struct hazptr_torture *rp;
+	struct hazptr_torture *rp1;
+
+	if (old_rp)
+		list_add(&old_rp->htort_free, &hazptr_torture_removed);
+	list_for_each_entry_safe(rp, rp1, &hazptr_torture_removed, htort_free) {
+		if (hazptr_torture_pipe_update_one(rp)) {
+			list_del(&rp->htort_free);
+			hazptr_torture_free(rp);
+		}
+	}
+}
+
+/*
+ * Operations vector for selecting different types of tests.
+ */
+
+struct hazptr_torture_ops {
+	void (*init)(void);
+	void (*cleanup)(void);
+	struct hazptr_torture *((*readlock)(struct hazptr_ctx **hcpp));
+	void (*read_delay)(struct torture_random_state *rrsp);
+	void (*readunlock)(struct hazptr_ctx *hcp, struct hazptr_torture *htp);
+	// @@@ int (*readlock_held)(void);   // lockdep.
+	// @@@ int (*readlock_nesting)(void); // actual nesting, if available, -1 if not.
+	// @@@ void (*deferred_free)(struct rcu_torture *p); @@@ call_hazptr()
+	void (*sync)(void *htp);
+	// @@@ void (*stats)(void); If statistics must be extracted from hazptr.c.
+	int irq_capable;
+	int must_free_ctx;
+	const char *name;
+};
+
+static struct hazptr_torture_ops *cur_ops;
+
+/*
+ * Definitions for hazard-pointer torture testing.
+ */
+
+static struct hazptr_torture *hazptr_torture_read_lock(struct hazptr_ctx **hcpp)
+{
+	struct hazptr_ctx *hcp = kmalloc(sizeof(*hcp), GFP_KERNEL);
+
+	*hcpp = hcp;
+	if (!hcp)
+		return NULL;
+	return (struct hazptr_torture *)hazptr_acquire(hcp, (void *)&hazptr_torture_current);
+}
+
+static void hazptr_read_delay(struct torture_random_state *rrsp)
+{
+	const unsigned long shortdelay_us = 200;
+	unsigned long longdelay_ms = 300;
+
+	/* We want a short delay sometimes to make a reader delay the grace
+	 * period, and we want a long delay occasionally to trigger
+	 * force_quiescent_state. */
+
+	if (!(torture_random(rrsp) % (nrealreaders * 2000 * longdelay_ms))) {
+		if ((preempt_count() & HARDIRQ_MASK) || softirq_count())
+			longdelay_ms = 5; /* Avoid triggering BH limits. */
+		mdelay(longdelay_ms);
+	}
+	if (!(torture_random(rrsp) % (nrealreaders * 2 * shortdelay_us)))
+		udelay(shortdelay_us);
+	if (!preempt_count() && !(torture_random(rrsp) % (nrealreaders * 500)))
+		torture_preempt_schedule();  /* QS only if preemptible. */
+}
+
+static void hazptr_torture_read_unlock(struct hazptr_ctx *hcp, struct hazptr_torture *htp)
+{
+	if (hcp) {
+		hazptr_release(hcp, htp);
+		if (cur_ops->must_free_ctx)
+			kfree(hcp);
+	}
+}
+
+static void hazptr_sync_torture_init(void)
+{
+	INIT_LIST_HEAD(&hazptr_torture_removed);
+}
+
+static struct hazptr_torture_ops hazptr_ops = {
+	.init			= hazptr_sync_torture_init,
+	.readlock		= hazptr_torture_read_lock,
+	.read_delay		= hazptr_read_delay,
+	.readunlock		= hazptr_torture_read_unlock,
+	.sync			= hazptr_synchronize,
+	.irq_capable		= 1,
+	.must_free_ctx		= 1,
+	.name			= "hazptr"
+};
+
+/*
+ * Hazard-pointer torture writer kthread.  Repeatedly substitutes a new
+ * structure for that pointed to by hazptr_torture_current, freeing the
+ * old structure after a series of timeouts (the "pipeline").
+ */
+static int
+hazptr_torture_writer(void *arg)
+{
+	bool booting_still = false;
+	int i;
+	unsigned long j;
+	int oldnice = task_nice(current);
+	struct hazptr_torture *rp;
+	struct hazptr_torture *old_rp;
+	static DEFINE_TORTURE_RANDOM(rand);
+	bool stutter_waited;
+
+	VERBOSE_TOROUT_STRING("hazptr_torture_writer task started");
+	// If the system is still booting, let it finish.
+	j = jiffies;
+	while (!torture_must_stop() && !rcu_inkernel_boot_has_ended()) {
+		booting_still = true;
+		schedule_timeout_interruptible(HZ);
+	}
+	if (booting_still)
+		pr_alert("%s" TORTURE_FLAG " Waited %lu jiffies for boot to complete.\n",
+			 torture_type, jiffies - j);
+
+	do {
+		hazptr_torture_writer_state = HTWS_FIXED_DELAY;
+		torture_hrtimeout_us(500, 1000, &rand);
+		rp = hazptr_torture_alloc();
+		if (rp == NULL)
+			continue;
+		rp->htort_pipe_count = 0;
+		ASSERT_EXCLUSIVE_WRITER(rp->htort_pipe_count);
+		hazptr_torture_writer_state = HTWS_DELAY;
+		udelay(torture_random(&rand) & 0x3ff);
+		hazptr_torture_writer_state = HTWS_REPLACE;
+		old_rp = READ_ONCE(hazptr_torture_current);
+		smp_store_release(&hazptr_torture_current, rp);
+		smp_wmb(); /* Mods to old_rp must follow smp_store_release() */
+		if (old_rp) {
+			i = old_rp->htort_pipe_count;
+			if (i > HAZPTR_TORTURE_PIPE_LEN)
+				i = HAZPTR_TORTURE_PIPE_LEN;
+			atomic_inc(&hazptr_torture_wcount[i]);
+			WRITE_ONCE(old_rp->htort_pipe_count,
+				   old_rp->htort_pipe_count + 1);
+			ASSERT_EXCLUSIVE_WRITER(old_rp->htort_pipe_count);
+
+			hazptr_torture_writer_state = HTWS_SYNC;
+			cur_ops->sync((void *)old_rp);
+			hazptr_torture_pipe_update(old_rp);
+		}
+
+		WRITE_ONCE(hazptr_torture_current_version, hazptr_torture_current_version + 1);
+		hazptr_torture_writer_state = HTWS_STUTTER;
+		stutter_waited = stutter_wait("hazptr_torture_writer");
+		if (stutter_waited && !torture_must_stop())
+			for (i = 0; i < ARRAY_SIZE(hazptr_tortures); i++)
+				if (list_empty(&hazptr_tortures[i].htort_free) &&
+				    READ_ONCE(hazptr_torture_current) != &hazptr_tortures[i]) {
+					tracing_off();
+					WARN(1, "%s: htort_pipe_count: %d\n", __func__, hazptr_tortures[i].htort_pipe_count);
+					rcu_ftrace_dump(DUMP_ALL);
+					break;
+				}
+		if (stutter_waited)
+			sched_set_normal(current, oldnice);
+	} while (!torture_must_stop());
+	hazptr_torture_current = NULL;  // Let stats task know that we are done.
+	hazptr_torture_writer_state = HTWS_STOPPING;
+	torture_kthread_stopping("hazptr_torture_writer");
+	return 0;
+}
+
+/*
+ * Hazard-pointer torture reader kthread.  Repeatedly dereferences
+ * hazptr_torture_current, incrementing the corresponding element of the
+ * pipeline array.  The counter in the element should never be greater
+ * than 1, otherwise, the hazard-pointer implementation is broken.
+ */
+static int hazptr_torture_reader(void *arg)
+{
+	struct hazptr_ctx *hcp;
+	struct hazptr_torture *htp;
+	unsigned long lastsleep = jiffies;
+	long myid = (long)arg;
+	int mynumonline = myid;
+	int pipe_count;
+	DEFINE_TORTURE_RANDOM(rand);
+
+	VERBOSE_TOROUT_STRING("hazptr_torture_reader task started");
+	set_user_nice(current, MAX_NICE);
+	do {
+		htp = cur_ops->readlock(&hcp);
+		if (!htp) {
+			schedule_timeout_interruptible(HZ / 10);
+			continue;
+		}
+		if (time_after(jiffies, lastsleep) && !torture_must_stop()) {
+			torture_hrtimeout_us(500, 1000, &rand);
+			lastsleep = jiffies + 10;
+		}
+		cur_ops->read_delay(&rand);
+		preempt_disable();
+		pipe_count = READ_ONCE(htp->htort_pipe_count);
+		if (pipe_count > HAZPTR_TORTURE_PIPE_LEN) {
+			// Should not happen in a correct RCU implementation,
+			// happens quite often for torture_type=busted.
+			pipe_count = HAZPTR_TORTURE_PIPE_LEN;
+		}
+		if (pipe_count > 1)
+			rcu_ftrace_dump(DUMP_ALL);
+		__this_cpu_inc(hazptr_torture_count[pipe_count]);
+		preempt_enable();
+		cur_ops->readunlock(hcp, htp);
+		while (!torture_must_stop() &&
+		       (torture_num_online_cpus() < mynumonline || !rcu_inkernel_boot_has_ended()))
+			schedule_timeout_interruptible(HZ / 5);
+		stutter_wait("hazptr_torture_reader");
+	} while (!torture_must_stop());
+	torture_kthread_stopping("hazptr_torture_reader");
+	return 0;
+}
+
+/*
+ * Print torture statistics.  Caller must ensure that there is only one
+ * call to this function at a given time!!!  This is normally accomplished
+ * by relying on the module system to only have one copy of the module
+ * loaded, and then by giving the hazptr_torture_stats kthread full control
+ * (or the init/cleanup functions when hazptr_torture_stats thread is
+ * not running).
+ */
+static void
+hazptr_torture_stats_print(void)
+{
+	const char *cp = hazptr_torture_writer_state_getname();;
+	int cpu;
+	int i;
+	long pipesummary[HAZPTR_TORTURE_PIPE_LEN + 1] = { 0 };
+	long batchsummary[HAZPTR_TORTURE_PIPE_LEN + 1] = { 0 };
+	struct hazptr_torture *rtcp;
+	static unsigned long rtcv_snap = ULONG_MAX;
+	static bool splatted;
+	struct task_struct *wtp;
+
+	for_each_possible_cpu(cpu)
+		for (i = 0; i < HAZPTR_TORTURE_PIPE_LEN + 1; i++)
+			pipesummary[i] += READ_ONCE(per_cpu(hazptr_torture_count, cpu)[i]);
+	for (i = HAZPTR_TORTURE_PIPE_LEN; i >= 0; i--) {
+		if (pipesummary[i] != 0)
+			break;
+	} // The value of variable "i" is used later, so don't clobber it!
+
+	pr_alert("%s%s ", torture_type, TORTURE_FLAG);
+	rtcp = READ_ONCE(hazptr_torture_current);
+	pr_cont("rtc: %p %s: %lu %s tfle: %d rta: %d rtaf: %d rtf: %d ",
+		rtcp,
+		rtcp && !rcu_stall_is_suppressed_at_boot() ? "ver" : "VER",
+		hazptr_torture_current_version,
+		cp,
+		list_empty(&hazptr_torture_freelist),
+		atomic_read(&n_hazptr_torture_alloc),
+		atomic_read(&n_hazptr_torture_alloc_fail),
+		atomic_read(&n_hazptr_torture_free));
+	torture_onoff_stats();
+
+	pr_alert("%s%s ", torture_type, TORTURE_FLAG);
+	if (i > 1) {
+		pr_cont("%s", "!!! ");
+		atomic_inc(&n_hazptr_torture_error);
+		WARN_ON_ONCE(i > 1); // Too-short grace period
+	}
+	pr_cont("Reader Pipe: ");
+	for (i = 0; i < HAZPTR_TORTURE_PIPE_LEN + 1; i++)
+		pr_cont(" %ld", pipesummary[i]);
+	pr_cont("\n");
+
+	pr_alert("%s%s ", torture_type, TORTURE_FLAG);
+	pr_cont("Reader Batch: ");
+	for (i = 0; i < HAZPTR_TORTURE_PIPE_LEN + 1; i++)
+		pr_cont(" %ld", batchsummary[i]);
+	pr_cont("\n");
+
+	pr_alert("%s%s ", torture_type, TORTURE_FLAG);
+	pr_cont("Free-Block Circulation: ");
+	for (i = 0; i < HAZPTR_TORTURE_PIPE_LEN + 1; i++) {
+		pr_cont(" %d", atomic_read(&hazptr_torture_wcount[i]));
+	}
+	pr_cont("\n");
+
+	if (rtcv_snap == hazptr_torture_current_version &&
+	    READ_ONCE(hazptr_torture_current) &&
+	    rcu_inkernel_boot_has_ended()) {
+		int __maybe_unused flags = 0;
+		unsigned long __maybe_unused gp_seq = 0;
+
+		wtp = READ_ONCE(writer_task);
+		pr_alert("??? Writer stall state %s(%d) g%lu f%#x ->state %#x cpu %d\n",
+			 hazptr_torture_writer_state_getname(),
+			 hazptr_torture_writer_state, gp_seq, flags,
+			 wtp == NULL ? ~0U : wtp->__state,
+			 wtp == NULL ? -1 : (int)task_cpu(wtp));
+		if (!splatted && wtp) {
+			sched_show_task(wtp);
+			splatted = true;
+		}
+		rcu_ftrace_dump(DUMP_ALL);
+	}
+	rtcv_snap = hazptr_torture_current_version;
+}
+
+/*
+ * Periodically prints torture statistics, if periodic statistics printing
+ * was specified via the stat_interval module parameter.
+ */
+static int
+hazptr_torture_stats(void *arg)
+{
+	VERBOSE_TOROUT_STRING("hazptr_torture_stats task started");
+	do {
+		schedule_timeout_interruptible(stat_interval * HZ);
+		hazptr_torture_stats_print();
+		torture_shutdown_absorb("hazptr_torture_stats");
+	} while (!torture_must_stop());
+	torture_kthread_stopping("hazptr_torture_stats");
+	return 0;
+}
+
+static void
+hazptr_torture_print_module_parms(struct hazptr_torture_ops *cur_ops, const char *tag)
+{
+	pr_alert("%s" TORTURE_FLAG
+		 "--- %s: nreaders=%d "
+		 "stat_interval=%d verbose=%d "
+		 "shuffle_interval=%d stutter=%d irqreader=%d "
+		 "onoff_interval=%d onoff_holdoff=%d\n",
+		 torture_type, tag, nrealreaders,
+		 stat_interval, verbose,
+		 shuffle_interval, stutter, irqreader,
+		 onoff_interval, onoff_holdoff);
+}
+
+// Randomly preempt online CPUs.
+static int hazptr_torture_preempt(void *unused)
+{
+	int cpu = -1;
+	DEFINE_TORTURE_RANDOM(rand);
+
+	schedule_timeout_idle(onoff_holdoff * HZ);
+	do {
+		// Wait for preempt_interval ms with up to 100us fuzz.
+		torture_hrtimeout_ms(preempt_interval, 100, &rand);
+		// Select online CPU.
+		cpu = cpumask_next(cpu, cpu_online_mask);
+		if (cpu >= nr_cpu_ids)
+			cpu = cpumask_next(-1, cpu_online_mask);
+		WARN_ON_ONCE(cpu >= nr_cpu_ids);
+		// Move to that CPU, if can't do so, retry later.
+		if (torture_sched_setaffinity(current->pid, cpumask_of(cpu), false))
+			continue;
+		// Preempt at high-ish priority, then reset to normal.
+		sched_set_fifo(current);
+		torture_sched_setaffinity(current->pid, cpu_present_mask, true);
+		mdelay(preempt_duration);
+		sched_set_normal(current, 0);
+		stutter_wait("hazptr_torture_preempt");
+	} while (!torture_must_stop());
+	torture_kthread_stopping("hazptr_torture_preempt");
+	return 0;
+}
+
+static void
+hazptr_torture_cleanup(void)
+{
+	int i;
+
+	if (torture_cleanup_begin())
+		return;
+	if (!cur_ops) {
+		torture_cleanup_end();
+		return;
+	}
+
+	torture_stop_kthread(hazptr_torture_preempt, preempt_task);
+	torture_stop_kthread(hazptr_torture_writer, writer_task);
+
+	if (reader_tasks) {
+		for (i = 0; i < nrealreaders; i++)
+			torture_stop_kthread(hazptr_torture_reader,
+					     reader_tasks[i]);
+		kfree(reader_tasks);
+		reader_tasks = NULL;
+	}
+
+	torture_stop_kthread(hazptr_torture_stats, stats_task);
+
+	/* Do torture-type-specific cleanup operations.  */
+	if (cur_ops->cleanup != NULL)
+		cur_ops->cleanup();
+
+	hazptr_torture_stats_print();  /* -After- the stats thread is stopped! */
+	if (atomic_read(&n_hazptr_torture_error))
+		hazptr_torture_print_module_parms(cur_ops, "End of test: FAILURE");
+	else if (torture_onoff_failures())
+		hazptr_torture_print_module_parms(cur_ops, "End of test: HAZPTR_HOTPLUG");
+	else
+		hazptr_torture_print_module_parms(cur_ops, "End of test: SUCCESS");
+	torture_cleanup_end();
+}
+
+static int __init hazptr_torture_init(void)
+{
+	long i;
+	int cpu;
+	int firsterr = 0;
+	static struct hazptr_torture_ops *torture_ops[] = { &hazptr_ops, };
+
+	if (!torture_init_begin(torture_type, verbose))
+		return -EBUSY;
+
+	/* Process args and tell the world that the torturer is on the job. */
+	for (i = 0; i < ARRAY_SIZE(torture_ops); i++) {
+		cur_ops = torture_ops[i];
+		if (strcmp(torture_type, cur_ops->name) == 0)
+			break;
+	}
+	if (i == ARRAY_SIZE(torture_ops)) {
+		pr_alert("hazptr-torture: invalid torture type: \"%s\"\n", torture_type);
+		pr_alert("hazptr-torture types:");
+		for (i = 0; i < ARRAY_SIZE(torture_ops); i++)
+			pr_cont(" %s", torture_ops[i]->name);
+		pr_cont("\n");
+		firsterr = -EINVAL;
+		cur_ops = NULL;
+		goto unwind;
+	}
+
+	if (cur_ops->init)
+		cur_ops->init();
+
+	if (nreaders >= 0) {
+		nrealreaders = nreaders;
+	} else {
+		nrealreaders = num_online_cpus() - 2 - nreaders;
+		if (nrealreaders <= 0)
+			nrealreaders = 1;
+	}
+	hazptr_torture_print_module_parms(cur_ops, "Start of test");
+
+	/* Set up the freelist. */
+	INIT_LIST_HEAD(&hazptr_torture_freelist);
+	for (i = 0; i < ARRAY_SIZE(hazptr_tortures); i++)
+		list_add_tail(&hazptr_tortures[i].htort_free, &hazptr_torture_freelist);
+
+	/* Initialize the statistics so that each run gets its own numbers. */
+
+	hazptr_torture_current = NULL;
+	hazptr_torture_current_version = 0;
+	atomic_set(&n_hazptr_torture_alloc, 0);
+	atomic_set(&n_hazptr_torture_alloc_fail, 0);
+	atomic_set(&n_hazptr_torture_free, 0);
+	atomic_set(&n_hazptr_torture_error, 0);
+	for (i = 0; i < HAZPTR_TORTURE_PIPE_LEN + 1; i++)
+		atomic_set(&hazptr_torture_wcount[i], 0);
+	for_each_possible_cpu(cpu) {
+		for (i = 0; i < HAZPTR_TORTURE_PIPE_LEN + 1; i++)
+			per_cpu(hazptr_torture_count, cpu)[i] = 0;
+	}
+
+	/* Start up the kthreads. */
+
+	reader_tasks = kzalloc_objs(reader_tasks[0], nrealreaders);
+	for (i = 0; i < nrealreaders; i++) {
+		firsterr = torture_create_kthread(hazptr_torture_reader, (void *)i,
+						  reader_tasks[i]);
+		if (torture_init_error(firsterr))
+			goto unwind;
+	}
+
+	firsterr = torture_create_kthread(hazptr_torture_writer, NULL, writer_task);
+	if (torture_init_error(firsterr))
+		goto unwind;
+
+	if (stat_interval > 0) {
+		firsterr = torture_create_kthread(hazptr_torture_stats, NULL, stats_task);
+		if (torture_init_error(firsterr))
+			goto unwind;
+	}
+	if (shuffle_interval > 0) {
+		firsterr = torture_shuffle_init(shuffle_interval * HZ);
+		if (torture_init_error(firsterr))
+			goto unwind;
+	}
+	if (stutter < 0)
+		stutter = 0;
+	if (stutter) {
+		int t;
+
+		t = stutter * HZ;
+		firsterr = torture_stutter_init(stutter * HZ, t);
+		if (torture_init_error(firsterr))
+			goto unwind;
+	}
+	firsterr = torture_shutdown_init(shutdown_secs, hazptr_torture_cleanup);
+	if (torture_init_error(firsterr))
+		goto unwind;
+	if (preempt_duration > 0) {
+		firsterr = torture_create_kthread(hazptr_torture_preempt, NULL, preempt_task);
+		if (torture_init_error(firsterr))
+			goto unwind;
+	}
+
+	torture_init_end();
+	return 0;
+
+unwind:
+	torture_init_end();
+	hazptr_torture_cleanup();
+	if (shutdown_secs) {
+		WARN_ON(!IS_MODULE(CONFIG_HAZPTR_TORTURE_TEST));
+		kernel_power_off();
+	}
+	return firsterr;
+}
+
+module_init(hazptr_torture_init);
+module_exit(hazptr_torture_cleanup);
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index b62735a6788423..2a778b8ab4ad78 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -44,6 +44,7 @@
 #include <linux/slab.h>
 #include <linux/irq_work.h>
 #include <linux/rcupdate_trace.h>
+#include <linux/torture.h>
 
 #define CREATE_TRACE_POINTS
 
@@ -525,7 +526,7 @@ EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
 	do { } while (0)
 #endif
 
-#if IS_ENABLED(CONFIG_RCU_TORTURE_TEST) || IS_MODULE(CONFIG_RCU_TORTURE_TEST) || IS_ENABLED(CONFIG_LOCK_TORTURE_TEST) || IS_MODULE(CONFIG_LOCK_TORTURE_TEST)
+#if IS_ENABLED(CONFIG_RCU_TORTURE_TEST) || IS_ENABLED(CONFIG_LOCK_TORTURE_TEST) || IS_ENABLED(CONFIG_HAZPTR_TORTURE_TEST)
 /* Get rcutorture access to sched_setaffinity(). */
 long torture_sched_setaffinity(pid_t pid, const struct cpumask *in_mask, bool dowarn)
 {
diff --git a/tools/testing/selftests/rcutorture/bin/kvm.sh b/tools/testing/selftests/rcutorture/bin/kvm.sh
index dfb73a3461a6df..14570f5e3ce17b 100755
--- a/tools/testing/selftests/rcutorture/bin/kvm.sh
+++ b/tools/testing/selftests/rcutorture/bin/kvm.sh
@@ -91,7 +91,7 @@ usage () {
 	echo "       --remote"
 	echo "       --results absolute-pathname"
 	echo "       --shutdown-grace seconds"
-	echo "       --torture lock|rcu|rcuscale|refscale|repro|scf|X*"
+	echo "       --torture hazptr|lock|rcu|rcuscale|refscale|repro|scf|X*"
 	echo "       --trust-make"
 	exit 1
 }
@@ -256,9 +256,9 @@ do
 		shift
 		;;
 	--torture)
-		checkarg --torture "(suite name)" "$#" "$2" '^\(lock\|rcu\|rcuscale\|refscale\|repro\|scf\|X.*\)$' '^--'
+		checkarg --torture "(suite name)" "$#" "$2" '^\(hazptr\|lock\|rcu\|rcuscale\|refscale\|repro\|scf\|X.*\)$' '^--'
 		TORTURE_SUITE=$2
-		TORTURE_MOD="`echo $TORTURE_SUITE | sed -e 's/^\(lock\|rcu\|scf\)$/\1torture/'`"
+		TORTURE_MOD="`echo $TORTURE_SUITE | sed -e 's/^\(hazptr\|lock\|rcu\|scf\)$/\1torture/'`"
 		shift
 		if test "$TORTURE_SUITE" = rcuscale || test "$TORTURE_SUITE" = refscale
 		then
diff --git a/tools/testing/selftests/rcutorture/configs/hazptr/CFLIST b/tools/testing/selftests/rcutorture/configs/hazptr/CFLIST
new file mode 100644
index 00000000000000..4d62eb4a39f999
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/hazptr/CFLIST
@@ -0,0 +1,2 @@
+NOPREEMPT
+PREEMPT
diff --git a/tools/testing/selftests/rcutorture/configs/hazptr/CFcommon b/tools/testing/selftests/rcutorture/configs/hazptr/CFcommon
new file mode 100644
index 00000000000000..c440d227007dce
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/hazptr/CFcommon
@@ -0,0 +1,2 @@
+CONFIG_HAZPTR_TORTURE_TEST=y
+CONFIG_PRINTK_TIME=y
diff --git a/tools/testing/selftests/rcutorture/configs/hazptr/NOPREEMPT b/tools/testing/selftests/rcutorture/configs/hazptr/NOPREEMPT
new file mode 100644
index 00000000000000..e2da430abe4d70
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/hazptr/NOPREEMPT
@@ -0,0 +1,17 @@
+CONFIG_SMP=y
+CONFIG_NR_CPUS=16
+CONFIG_PREEMPT_LAZY=y
+CONFIG_PREEMPT_NONE=n
+CONFIG_PREEMPT_VOLUNTARY=n
+CONFIG_PREEMPT=n
+CONFIG_PREEMPT_DYNAMIC=n
+CONFIG_HZ_PERIODIC=n
+CONFIG_NO_HZ_IDLE=y
+CONFIG_NO_HZ_FULL=n
+CONFIG_HOTPLUG_CPU=y
+CONFIG_SUSPEND=n
+CONFIG_HIBERNATION=n
+CONFIG_DEBUG_LOCK_ALLOC=n
+CONFIG_PROVE_LOCKING=n
+CONFIG_KPROBES=n
+CONFIG_FTRACE=n
diff --git a/tools/testing/selftests/rcutorture/configs/hazptr/PREEMPT b/tools/testing/selftests/rcutorture/configs/hazptr/PREEMPT
new file mode 100644
index 00000000000000..b8ea4364b20b7b
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/hazptr/PREEMPT
@@ -0,0 +1,14 @@
+CONFIG_SMP=y
+CONFIG_NR_CPUS=16
+CONFIG_PREEMPT_NONE=n
+CONFIG_PREEMPT_VOLUNTARY=n
+CONFIG_PREEMPT=y
+CONFIG_HZ_PERIODIC=n
+CONFIG_NO_HZ_IDLE=y
+CONFIG_NO_HZ_FULL=n
+CONFIG_HOTPLUG_CPU=y
+CONFIG_SUSPEND=n
+CONFIG_HIBERNATION=n
+CONFIG_DEBUG_LOCK_ALLOC=n
+CONFIG_PROVE_LOCKING=n
+CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
diff --git a/tools/testing/selftests/rcutorture/configs/hazptr/ver_functions.sh b/tools/testing/selftests/rcutorture/configs/hazptr/ver_functions.sh
new file mode 100644
index 00000000000000..a28ea2f292e453
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/hazptr/ver_functions.sh
@@ -0,0 +1,40 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0+
+#
+# Kernel-version-dependent shell functions for the rest of the scripts.
+#
+# Claude created this file, and I quote:
+#
+#	"I created [this file] modeled on the lock torture
+#	version. It defines per_version_boot_params to pass
+#	hazptrtorture.shutdown_secs=$3, hazptrtorture.stat_interval=15,
+#	hazptrtorture.verbose=1, and optional CPU-hotplug parameters to
+#	the kernel command line."
+#
+# I therefore kept locktorture's ver_functions.sh copyright notice:
+#
+# Copyright (C) Meta Platforms, Inc. and affiliates.
+#
+# Authors: Paul E. McKenney <paulmck@kernel.org>
+
+# hazptrtorture_param_onoff bootparam-string config-file
+#
+# Adds onoff hazptrtorture module parameters to kernels having it.
+hazptrtorture_param_onoff () {
+	if ! bootparam_hotplug_cpu "$1" && configfrag_hotplug_cpu "$2"
+	then
+		echo CPU-hotplug kernel, adding hazptrtorture onoff. 1>&2
+		echo hazptrtorture.onoff_interval=3 hazptrtorture.onoff_holdoff=30
+	fi
+}
+
+# per_version_boot_params bootparam-string config-file seconds
+#
+# Adds per-version torture-module parameters to kernels supporting them.
+per_version_boot_params () {
+	echo	`hazptrtorture_param_onoff "$1" "$2"` \
+		hazptrtorture.stat_interval=15 \
+		hazptrtorture.shutdown_secs=$3 \
+		hazptrtorture.verbose=1 \
+		$1
+}
-- 
2.40.1