x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

When using eBPF to probe CS CALL instructions within a function,
a crash can be triggered.

The eBPF tool probes offset 257 of the __hrtimer_run_queues()
function:

<__hrtimer_run_queues+249>:  nopl   0x0(%rax,%rax,1)
<__hrtimer_run_queues+254>:  mov    %r14,%rdi
<__hrtimer_run_queues+257>:  cs call <__x86_indirect_thunk_r12>
<__hrtimer_run_queues+263>:  mov    %eax,%r12d
<__hrtimer_run_queues+266>:  xchg   %ax,%ax
<__hrtimer_run_queues+268>:  mov    %r13,%rdi

Which triggers this crash:

  BUG: unable to handle page fault for address: 00000000000f41c9
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0002) - not-present page
  PGD 0 P4D 0
  Oops: 0002 [#1] SMP NOPTI
  CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P
  RIP: 0010:__hrtimer_run_queues+0x106/0x230

Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is
at the 6th byte of the above CS CALL instruction. Since the CS CALL
instruction occupies 6 bytes, the exception occurred in the middle of that
call instruction.

The root cause is that when using eBPF tools to probe in the middle of a
function, a kprobe with INT3 is used as the underlying implementation.

During single-step emulation of the original CALL instruction,
int3_emulate_call() assumes that the probed CALL instruction is 5 bytes
long. However, the actual CS-prefixed CALL instruction occupies 6 bytes,
so it constructs an incorrect exception return address. When the CPU
returns from the kprobe handler, the next instruction to be executed is at
the address of the last byte of that CS CALL instruction. Coincidentally,
starting from that address, the CPU fetches and decodes a completely
different instruction, which ultimately triggers a kernel crash.

Fix the issue by using the actual instruction length obtained from
the instruction decoder when constructing the exception return
address, rather than relying on the hardcoded CALL_INSN_SIZE macro.

[ mingo: Refined the changelog ]

Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step")
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

1 files changed, 681 insertions, 0 deletions

diff --git a/lib/test_objpool.c b/lib/test_objpool.c
new file mode 100644
index 000000000..6a34a7582
--- /dev/null
+++ b/lib/test_objpool.c
@@ -0,0 +1,681 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Test module for lockless object pool
+ *
+ * Copyright: wuqiang.matt@bytedance.com
+ */
+
+#include <linux/errno.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/completion.h>
+#include <linux/kthread.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/delay.h>
+#include <linux/hrtimer.h>
+#include <linux/objpool.h>
+
+#define OT_NR_MAX_BULK (16)
+
+/* memory usage */
+struct ot_mem_stat {
+	atomic_long_t alloc;
+	atomic_long_t free;
+};
+
+/* object allocation results */
+struct ot_obj_stat {
+	unsigned long nhits;
+	unsigned long nmiss;
+};
+
+/* control & results per testcase */
+struct ot_data {
+	struct rw_semaphore start;
+	struct completion wait;
+	struct completion rcu;
+	atomic_t nthreads ____cacheline_aligned_in_smp;
+	atomic_t stop ____cacheline_aligned_in_smp;
+	struct ot_mem_stat kmalloc;
+	struct ot_mem_stat vmalloc;
+	struct ot_obj_stat objects;
+	u64    duration;
+};
+
+/* testcase */
+struct ot_test {
+	int async; /* synchronous or asynchronous */
+	int mode; /* only mode 0 supported */
+	int objsz; /* object size */
+	int duration; /* ms */
+	int delay; /* ms */
+	int bulk_normal;
+	int bulk_irq;
+	unsigned long hrtimer; /* ms */
+	const char *name;
+	struct ot_data data;
+};
+
+/* per-cpu worker */
+struct ot_item {
+	struct objpool_head *pool; /* pool head */
+	struct ot_test *test; /* test parameters */
+
+	void (*worker)(struct ot_item *item, int irq);
+
+	/* hrtimer control */
+	ktime_t hrtcycle;
+	struct hrtimer hrtimer;
+
+	int bulk[2]; /* for thread and irq */
+	int delay;
+	u32 niters;
+
+	/* summary per thread */
+	struct ot_obj_stat stat[2]; /* thread and irq */
+	u64 duration;
+};
+
+/*
+ * memory leakage checking
+ */
+
+static void *ot_kzalloc(struct ot_test *test, long size)
+{
+	void *ptr = kzalloc(size, GFP_KERNEL);
+
+	if (ptr)
+		atomic_long_add(size, &test->data.kmalloc.alloc);
+	return ptr;
+}
+
+static void ot_kfree(struct ot_test *test, void *ptr, long size)
+{
+	if (!ptr)
+		return;
+	atomic_long_add(size, &test->data.kmalloc.free);
+	kfree(ptr);
+}
+
+static void ot_mem_report(struct ot_test *test)
+{
+	long alloc, free;
+
+	pr_info("memory allocation summary for %s\n", test->name);
+
+	alloc = atomic_long_read(&test->data.kmalloc.alloc);
+	free = atomic_long_read(&test->data.kmalloc.free);
+	pr_info("  kmalloc: %lu - %lu = %lu\n", alloc, free, alloc - free);
+
+	alloc = atomic_long_read(&test->data.vmalloc.alloc);
+	free = atomic_long_read(&test->data.vmalloc.free);
+	pr_info("  vmalloc: %lu - %lu = %lu\n", alloc, free, alloc - free);
+}
+
+/* user object instance */
+struct ot_node {
+	void *owner;
+	unsigned long data;
+	unsigned long refs;
+	unsigned long payload[32];
+};
+
+/* user objpool manager */
+struct ot_context {
+	struct objpool_head pool; /* objpool head */
+	struct ot_test *test; /* test parameters */
+	void *ptr; /* user pool buffer */
+	unsigned long size; /* buffer size */
+	struct rcu_head rcu;
+};
+
+static DEFINE_PER_CPU(struct ot_item, ot_pcup_items);
+
+static int ot_init_data(struct ot_data *data)
+{
+	memset(data, 0, sizeof(*data));
+	init_rwsem(&data->start);
+	init_completion(&data->wait);
+	init_completion(&data->rcu);
+	atomic_set(&data->nthreads, 1);
+
+	return 0;
+}
+
+static int ot_init_node(void *nod, void *context)
+{
+	struct ot_context *sop = context;
+	struct ot_node *on = nod;
+
+	on->owner = &sop->pool;
+	return 0;
+}
+
+static enum hrtimer_restart ot_hrtimer_handler(struct hrtimer *hrt)
+{
+	struct ot_item *item = container_of(hrt, struct ot_item, hrtimer);
+	struct ot_test *test = item->test;
+
+	if (atomic_read_acquire(&test->data.stop))
+		return HRTIMER_NORESTART;
+
+	/* do bulk-testings for objects pop/push */
+	item->worker(item, 1);
+
+	hrtimer_forward_now(hrt, item->hrtcycle);
+	return HRTIMER_RESTART;
+}
+
+static void ot_start_hrtimer(struct ot_item *item)
+{
+	if (!item->test->hrtimer)
+		return;
+	hrtimer_start(&item->hrtimer, item->hrtcycle, HRTIMER_MODE_REL);
+}
+
+static void ot_stop_hrtimer(struct ot_item *item)
+{
+	if (!item->test->hrtimer)
+		return;
+	hrtimer_cancel(&item->hrtimer);
+}
+
+static int ot_init_hrtimer(struct ot_item *item, unsigned long hrtimer)
+{
+	struct hrtimer *hrt = &item->hrtimer;
+
+	if (!hrtimer)
+		return -ENOENT;
+
+	item->hrtcycle = ktime_set(0, hrtimer * 1000000UL);
+	hrtimer_setup(hrt, ot_hrtimer_handler, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+	return 0;
+}
+
+static int ot_init_cpu_item(struct ot_item *item,
+			struct ot_test *test,
+			struct objpool_head *pool,
+			void (*worker)(struct ot_item *, int))
+{
+	memset(item, 0, sizeof(*item));
+	item->pool = pool;
+	item->test = test;
+	item->worker = worker;
+
+	item->bulk[0] = test->bulk_normal;
+	item->bulk[1] = test->bulk_irq;
+	item->delay = test->delay;
+
+	/* initialize hrtimer */
+	ot_init_hrtimer(item, item->test->hrtimer);
+	return 0;
+}
+
+static int ot_thread_worker(void *arg)
+{
+	struct ot_item *item = arg;
+	struct ot_test *test = item->test;
+	ktime_t start;
+
+	atomic_inc(&test->data.nthreads);
+	down_read(&test->data.start);
+	up_read(&test->data.start);
+	start = ktime_get();
+	ot_start_hrtimer(item);
+	do {
+		if (atomic_read_acquire(&test->data.stop))
+			break;
+		/* do bulk-testings for objects pop/push */
+		item->worker(item, 0);
+	} while (!kthread_should_stop());
+	ot_stop_hrtimer(item);
+	item->duration = (u64) ktime_us_delta(ktime_get(), start);
+	if (atomic_dec_and_test(&test->data.nthreads))
+		complete(&test->data.wait);
+
+	return 0;
+}
+
+static void ot_perf_report(struct ot_test *test, u64 duration)
+{
+	struct ot_obj_stat total, normal = {0}, irq = {0};
+	int cpu, nthreads = 0;
+
+	pr_info("\n");
+	pr_info("Testing summary for %s\n", test->name);
+
+	for_each_possible_cpu(cpu) {
+		struct ot_item *item = per_cpu_ptr(&ot_pcup_items, cpu);
+		if (!item->duration)
+			continue;
+		normal.nhits += item->stat[0].nhits;
+		normal.nmiss += item->stat[0].nmiss;
+		irq.nhits += item->stat[1].nhits;
+		irq.nmiss += item->stat[1].nmiss;
+		pr_info("CPU: %d  duration: %lluus\n", cpu, item->duration);
+		pr_info("\tthread:\t%16lu hits \t%16lu miss\n",
+			item->stat[0].nhits, item->stat[0].nmiss);
+		pr_info("\tirq:   \t%16lu hits \t%16lu miss\n",
+			item->stat[1].nhits, item->stat[1].nmiss);
+		pr_info("\ttotal: \t%16lu hits \t%16lu miss\n",
+			item->stat[0].nhits + item->stat[1].nhits,
+			item->stat[0].nmiss + item->stat[1].nmiss);
+		nthreads++;
+	}
+
+	total.nhits = normal.nhits + irq.nhits;
+	total.nmiss = normal.nmiss + irq.nmiss;
+
+	pr_info("ALL: \tnthreads: %d  duration: %lluus\n", nthreads, duration);
+	pr_info("SUM: \t%16lu hits \t%16lu miss\n",
+		total.nhits, total.nmiss);
+
+	test->data.objects = total;
+	test->data.duration = duration;
+}
+
+/*
+ * synchronous test cases for objpool manipulation
+ */
+
+/* objpool manipulation for synchronous mode (percpu objpool) */
+static struct ot_context *ot_init_sync_m0(struct ot_test *test)
+{
+	struct ot_context *sop = NULL;
+	int max = num_possible_cpus() << 3;
+	gfp_t gfp = GFP_KERNEL;
+
+	sop = (struct ot_context *)ot_kzalloc(test, sizeof(*sop));
+	if (!sop)
+		return NULL;
+	sop->test = test;
+	if (test->objsz < 512)
+		gfp = GFP_ATOMIC;
+
+	if (objpool_init(&sop->pool, max, test->objsz,
+			 gfp, sop, ot_init_node, NULL)) {
+		ot_kfree(test, sop, sizeof(*sop));
+		return NULL;
+	}
+	WARN_ON(max != sop->pool.nr_objs);
+
+	return sop;
+}
+
+static void ot_fini_sync(struct ot_context *sop)
+{
+	objpool_fini(&sop->pool);
+	ot_kfree(sop->test, sop, sizeof(*sop));
+}
+
+static struct {
+	struct ot_context * (*init)(struct ot_test *oc);
+	void (*fini)(struct ot_context *sop);
+} g_ot_sync_ops[] = {
+	{.init = ot_init_sync_m0, .fini = ot_fini_sync},
+};
+
+/*
+ * synchronous test cases: performance mode
+ */
+
+static void ot_bulk_sync(struct ot_item *item, int irq)
+{
+	struct ot_node *nods[OT_NR_MAX_BULK];
+	int i;
+
+	for (i = 0; i < item->bulk[irq]; i++)
+		nods[i] = objpool_pop(item->pool);
+
+	if (!irq && (item->delay || !(++(item->niters) & 0x7FFF)))
+		msleep(item->delay);
+
+	while (i-- > 0) {
+		struct ot_node *on = nods[i];
+		if (on) {
+			on->refs++;
+			objpool_push(on, item->pool);
+			item->stat[irq].nhits++;
+		} else {
+			item->stat[irq].nmiss++;
+		}
+	}
+}
+
+static int ot_start_sync(struct ot_test *test)
+{
+	struct ot_context *sop;
+	ktime_t start;
+	u64 duration;
+	unsigned long timeout;
+	int cpu;
+
+	/* initialize objpool for syncrhonous testcase */
+	sop = g_ot_sync_ops[test->mode].init(test);
+	if (!sop)
+		return -ENOMEM;
+
+	/* grab rwsem to block testing threads */
+	down_write(&test->data.start);
+
+	for_each_possible_cpu(cpu) {
+		struct ot_item *item = per_cpu_ptr(&ot_pcup_items, cpu);
+		struct task_struct *work;
+
+		ot_init_cpu_item(item, test, &sop->pool, ot_bulk_sync);
+
+		/* skip offline cpus */
+		if (!cpu_online(cpu))
+			continue;
+
+		work = kthread_run_on_cpu(ot_thread_worker, item,
+					  cpu, "ot_worker_%d");
+		if (IS_ERR(work))
+			pr_err("failed to create thread for cpu %d\n", cpu);
+	}
+
+	/* wait a while to make sure all threads waiting at start line */
+	msleep(20);
+
+	/* in case no threads were created: memory insufficient ? */
+	if (atomic_dec_and_test(&test->data.nthreads))
+		complete(&test->data.wait);
+
+	// sched_set_fifo_low(current);
+
+	/* start objpool testing threads */
+	start = ktime_get();
+	up_write(&test->data.start);
+
+	/* yeild cpu to worker threads for duration ms */
+	timeout = msecs_to_jiffies(test->duration);
+	schedule_timeout_interruptible(timeout);
+
+	/* tell workers threads to quit */
+	atomic_set_release(&test->data.stop, 1);
+
+	/* wait all workers threads finish and quit */
+	wait_for_completion(&test->data.wait);
+	duration = (u64) ktime_us_delta(ktime_get(), start);
+
+	/* cleanup objpool */
+	g_ot_sync_ops[test->mode].fini(sop);
+
+	/* report testing summary and performance results */
+	ot_perf_report(test, duration);
+
+	/* report memory allocation summary */
+	ot_mem_report(test);
+
+	return 0;
+}
+
+/*
+ * asynchronous test cases: pool lifecycle controlled by refcount
+ */
+
+static void ot_fini_async_rcu(struct rcu_head *rcu)
+{
+	struct ot_context *sop = container_of(rcu, struct ot_context, rcu);
+	struct ot_test *test = sop->test;
+
+	/* here all cpus are aware of the stop event: test->data.stop = 1 */
+	WARN_ON(!atomic_read_acquire(&test->data.stop));
+
+	objpool_fini(&sop->pool);
+	complete(&test->data.rcu);
+}
+
+static void ot_fini_async(struct ot_context *sop)
+{
+	/* make sure the stop event is acknowledged by all cores */
+	call_rcu(&sop->rcu, ot_fini_async_rcu);
+}
+
+static int ot_objpool_release(struct objpool_head *head, void *context)
+{
+	struct ot_context *sop = context;
+
+	WARN_ON(!head || !sop || head != &sop->pool);
+
+	/* do context cleaning if needed */
+	if (sop)
+		ot_kfree(sop->test, sop, sizeof(*sop));
+
+	return 0;
+}
+
+static struct ot_context *ot_init_async_m0(struct ot_test *test)
+{
+	struct ot_context *sop = NULL;
+	int max = num_possible_cpus() << 3;
+	gfp_t gfp = GFP_KERNEL;
+
+	sop = (struct ot_context *)ot_kzalloc(test, sizeof(*sop));
+	if (!sop)
+		return NULL;
+	sop->test = test;
+	if (test->objsz < 512)
+		gfp = GFP_ATOMIC;
+
+	if (objpool_init(&sop->pool, max, test->objsz, gfp, sop,
+			 ot_init_node, ot_objpool_release)) {
+		ot_kfree(test, sop, sizeof(*sop));
+		return NULL;
+	}
+	WARN_ON(max != sop->pool.nr_objs);
+
+	return sop;
+}
+
+static struct {
+	struct ot_context * (*init)(struct ot_test *oc);
+	void (*fini)(struct ot_context *sop);
+} g_ot_async_ops[] = {
+	{.init = ot_init_async_m0, .fini = ot_fini_async},
+};
+
+static void ot_nod_recycle(struct ot_node *on, struct objpool_head *pool,
+			int release)
+{
+	struct ot_context *sop;
+
+	on->refs++;
+
+	if (!release) {
+		/* push object back to opjpool for reuse */
+		objpool_push(on, pool);
+		return;
+	}
+
+	sop = container_of(pool, struct ot_context, pool);
+	WARN_ON(sop != pool->context);
+
+	/* unref objpool with nod removed forever */
+	objpool_drop(on, pool);
+}
+
+static void ot_bulk_async(struct ot_item *item, int irq)
+{
+	struct ot_test *test = item->test;
+	struct ot_node *nods[OT_NR_MAX_BULK];
+	int i, stop;
+
+	for (i = 0; i < item->bulk[irq]; i++)
+		nods[i] = objpool_pop(item->pool);
+
+	if (!irq) {
+		if (item->delay || !(++(item->niters) & 0x7FFF))
+			msleep(item->delay);
+		get_cpu();
+	}
+
+	stop = atomic_read_acquire(&test->data.stop);
+
+	/* drop all objects and deref objpool */
+	while (i-- > 0) {
+		struct ot_node *on = nods[i];
+
+		if (on) {
+			on->refs++;
+			ot_nod_recycle(on, item->pool, stop);
+			item->stat[irq].nhits++;
+		} else {
+			item->stat[irq].nmiss++;
+		}
+	}
+
+	if (!irq)
+		put_cpu();
+}
+
+static int ot_start_async(struct ot_test *test)
+{
+	struct ot_context *sop;
+	ktime_t start;
+	u64 duration;
+	unsigned long timeout;
+	int cpu;
+
+	/* initialize objpool for syncrhonous testcase */
+	sop = g_ot_async_ops[test->mode].init(test);
+	if (!sop)
+		return -ENOMEM;
+
+	/* grab rwsem to block testing threads */
+	down_write(&test->data.start);
+
+	for_each_possible_cpu(cpu) {
+		struct ot_item *item = per_cpu_ptr(&ot_pcup_items, cpu);
+		struct task_struct *work;
+
+		ot_init_cpu_item(item, test, &sop->pool, ot_bulk_async);
+
+		/* skip offline cpus */
+		if (!cpu_online(cpu))
+			continue;
+
+		work = kthread_run_on_cpu(ot_thread_worker, item, cpu, "ot_worker_%d");
+		if (IS_ERR(work))
+			pr_err("failed to create thread for cpu %d\n", cpu);
+	}
+
+	/* wait a while to make sure all threads waiting at start line */
+	msleep(20);
+
+	/* in case no threads were created: memory insufficient ? */
+	if (atomic_dec_and_test(&test->data.nthreads))
+		complete(&test->data.wait);
+
+	/* start objpool testing threads */
+	start = ktime_get();
+	up_write(&test->data.start);
+
+	/* yeild cpu to worker threads for duration ms */
+	timeout = msecs_to_jiffies(test->duration);
+	schedule_timeout_interruptible(timeout);
+
+	/* tell workers threads to quit */
+	atomic_set_release(&test->data.stop, 1);
+
+	/* do async-finalization */
+	g_ot_async_ops[test->mode].fini(sop);
+
+	/* wait all workers threads finish and quit */
+	wait_for_completion(&test->data.wait);
+	duration = (u64) ktime_us_delta(ktime_get(), start);
+
+	/* assure rcu callback is triggered */
+	wait_for_completion(&test->data.rcu);
+
+	/*
+	 * now we are sure that objpool is finalized either
+	 * by rcu callback or by worker threads
+	 */
+
+	/* report testing summary and performance results */
+	ot_perf_report(test, duration);
+
+	/* report memory allocation summary */
+	ot_mem_report(test);
+
+	return 0;
+}
+
+/*
+ * predefined testing cases:
+ *   synchronous case / overrun case / async case
+ *
+ * async: synchronous or asynchronous testing
+ * mode: only mode 0 supported
+ * objsz: object size
+ * duration: int, total test time in ms
+ * delay: int, delay (in ms) between each iteration
+ * bulk_normal: int, repeat times for thread worker
+ * bulk_irq: int, repeat times for irq consumer
+ * hrtimer: unsigned long, hrtimer intervnal in ms
+ * name: char *, tag for current test ot_item
+ */
+
+#define NODE_COMPACT sizeof(struct ot_node)
+#define NODE_VMALLOC (512)
+
+static struct ot_test g_testcases[] = {
+
+	/* sync & normal */
+	{0, 0, NODE_COMPACT, 1000, 0,  1,  0,  0, "sync: percpu objpool"},
+	{0, 0, NODE_VMALLOC, 1000, 0,  1,  0,  0, "sync: percpu objpool from vmalloc"},
+
+	/* sync & hrtimer */
+	{0, 0, NODE_COMPACT, 1000, 0,  1,  1,  4, "sync & hrtimer: percpu objpool"},
+	{0, 0, NODE_VMALLOC, 1000, 0,  1,  1,  4, "sync & hrtimer: percpu objpool from vmalloc"},
+
+	/* sync & overrun */
+	{0, 0, NODE_COMPACT, 1000, 0, 16,  0,  0, "sync overrun: percpu objpool"},
+	{0, 0, NODE_VMALLOC, 1000, 0, 16,  0,  0, "sync overrun: percpu objpool from vmalloc"},
+
+	/* async mode */
+	{1, 0, NODE_COMPACT, 1000, 100,  1,  0,  0, "async: percpu objpool"},
+	{1, 0, NODE_VMALLOC, 1000, 100,  1,  0,  0, "async: percpu objpool from vmalloc"},
+
+	/* async + hrtimer mode */
+	{1, 0, NODE_COMPACT, 1000, 0,  4,  4,  4, "async & hrtimer: percpu objpool"},
+	{1, 0, NODE_VMALLOC, 1000, 0,  4,  4,  4, "async & hrtimer: percpu objpool from vmalloc"},
+};
+
+static int __init ot_mod_init(void)
+{
+	int i;
+
+	/* perform testings */
+	for (i = 0; i < ARRAY_SIZE(g_testcases); i++) {
+		ot_init_data(&g_testcases[i].data);
+		if (g_testcases[i].async)
+			ot_start_async(&g_testcases[i]);
+		else
+			ot_start_sync(&g_testcases[i]);
+	}
+
+	/* show tests summary */
+	pr_info("\n");
+	pr_info("Summary of testcases:\n");
+	for (i = 0; i < ARRAY_SIZE(g_testcases); i++) {
+		pr_info("    duration: %lluus \thits: %10lu \tmiss: %10lu \t%s\n",
+			g_testcases[i].data.duration, g_testcases[i].data.objects.nhits,
+			g_testcases[i].data.objects.nmiss, g_testcases[i].name);
+	}
+
+	return -EAGAIN;
+}
+
+static void __exit ot_mod_exit(void)
+{
+}
+
+module_init(ot_mod_init);
+module_exit(ot_mod_exit);
+
+MODULE_DESCRIPTION("Test module for lockless object pool");
+MODULE_LICENSE("GPL");