summaryrefslogtreecommitdiff
path: root/kernel/time/clocksource-wdtest.c
blob: d06185e054ea2173f273c826098cb04dde7dd05f (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
// SPDX-License-Identifier: GPL-2.0+
/*
 * Unit test for the clocksource watchdog.
 *
 * Copyright (C) 2021 Facebook, Inc.
 *
 * Author: Paul E. McKenney <paulmck@kernel.org>
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/device.h>
#include <linux/clocksource.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
#include <linux/tick.h>
#include <linux/kthread.h>
#include <linux/delay.h>
#include <linux/prandom.h>
#include <linux/cpu.h>

#include "tick-internal.h"

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Paul E. McKenney <paulmck@kernel.org>");

static int holdoff = IS_BUILTIN(CONFIG_TEST_CLOCKSOURCE_WATCHDOG) ? 10 : 0;
module_param(holdoff, int, 0444);
MODULE_PARM_DESC(holdoff, "Time to wait to start test (s).");

/* Watchdog kthread's task_struct pointer for debug purposes. */
static struct task_struct *wdtest_task;

static u64 wdtest_jiffies_read(struct clocksource *cs)
{
	return (u64)jiffies;
}

static struct clocksource clocksource_wdtest_jiffies = {
	.name			= "wdtest-jiffies",
	.rating			= 1, /* lowest valid rating*/
	.uncertainty_margin	= TICK_NSEC,
	.read			= wdtest_jiffies_read,
	.mask			= CLOCKSOURCE_MASK(32),
	.flags			= CLOCK_SOURCE_MUST_VERIFY,
	.mult			= TICK_NSEC << JIFFIES_SHIFT, /* details above */
	.shift			= JIFFIES_SHIFT,
	.max_cycles		= 10,
};

static int wdtest_ktime_read_ndelays;
static bool wdtest_ktime_read_fuzz;

static u64 wdtest_ktime_read(struct clocksource *cs)
{
	int wkrn = READ_ONCE(wdtest_ktime_read_ndelays);
	static int sign = 1;
	u64 ret;

	if (wkrn) {
		udelay(cs->uncertainty_margin / 250);
		WRITE_ONCE(wdtest_ktime_read_ndelays, wkrn - 1);
	}
	ret = ktime_get_real_fast_ns();
	if (READ_ONCE(wdtest_ktime_read_fuzz)) {
		sign = -sign;
		ret = ret + sign * 100 * NSEC_PER_MSEC;
	}
	return ret;
}

static void wdtest_ktime_cs_mark_unstable(struct clocksource *cs)
{
	pr_info("--- Marking %s unstable due to clocksource watchdog.\n", cs->name);
}

#define KTIME_FLAGS (CLOCK_SOURCE_IS_CONTINUOUS | \
		     CLOCK_SOURCE_VALID_FOR_HRES | \
		     CLOCK_SOURCE_MUST_VERIFY | \
		     CLOCK_SOURCE_VERIFY_PERCPU)

static struct clocksource clocksource_wdtest_ktime = {
	.name			= "wdtest-ktime",
	.rating			= 300,
	.read			= wdtest_ktime_read,
	.mask			= CLOCKSOURCE_MASK(64),
	.flags			= KTIME_FLAGS,
	.mark_unstable		= wdtest_ktime_cs_mark_unstable,
	.list			= LIST_HEAD_INIT(clocksource_wdtest_ktime.list),
};

/* Reset the clocksource if needed. */
static void wdtest_ktime_clocksource_reset(void)
{
	if (clocksource_wdtest_ktime.flags & CLOCK_SOURCE_UNSTABLE) {
		clocksource_unregister(&clocksource_wdtest_ktime);
		clocksource_wdtest_ktime.flags = KTIME_FLAGS;
		schedule_timeout_uninterruptible(HZ / 10);
		clocksource_register_khz(&clocksource_wdtest_ktime, 1000 * 1000);
	}
}

/* Run the specified series of watchdog tests. */
static int wdtest_func(void *arg)
{
	unsigned long j1, j2;
	int i, max_retries;
	char *s;

	schedule_timeout_uninterruptible(holdoff * HZ);

	/*
	 * Verify that jiffies-like clocksources get the manually
	 * specified uncertainty margin.
	 */
	pr_info("--- Verify jiffies-like uncertainty margin.\n");
	__clocksource_register(&clocksource_wdtest_jiffies);
	WARN_ON_ONCE(clocksource_wdtest_jiffies.uncertainty_margin != TICK_NSEC);

	j1 = clocksource_wdtest_jiffies.read(&clocksource_wdtest_jiffies);
	schedule_timeout_uninterruptible(HZ);
	j2 = clocksource_wdtest_jiffies.read(&clocksource_wdtest_jiffies);
	WARN_ON_ONCE(j1 == j2);

	clocksource_unregister(&clocksource_wdtest_jiffies);

	/*
	 * Verify that tsc-like clocksources are assigned a reasonable
	 * uncertainty margin.
	 */
	pr_info("--- Verify tsc-like uncertainty margin.\n");
	clocksource_register_khz(&clocksource_wdtest_ktime, 1000 * 1000);
	WARN_ON_ONCE(clocksource_wdtest_ktime.uncertainty_margin < NSEC_PER_USEC);

	j1 = clocksource_wdtest_ktime.read(&clocksource_wdtest_ktime);
	udelay(1);
	j2 = clocksource_wdtest_ktime.read(&clocksource_wdtest_ktime);
	pr_info("--- tsc-like times: %lu - %lu = %lu.\n", j2, j1, j2 - j1);
	WARN_ON_ONCE(time_before(j2, j1 + NSEC_PER_USEC));

	/* Verify tsc-like stability with various numbers of errors injected. */
	max_retries = clocksource_get_max_watchdog_retry();
	for (i = 0; i <= max_retries + 1; i++) {
		if (i <= 1 && i < max_retries)
			s = "";
		else if (i <= max_retries)
			s = ", expect message";
		else
			s = ", expect clock skew";
		pr_info("--- Watchdog with %dx error injection, %d retries%s.\n", i, max_retries, s);
		WRITE_ONCE(wdtest_ktime_read_ndelays, i);
		schedule_timeout_uninterruptible(2 * HZ);
		WARN_ON_ONCE(READ_ONCE(wdtest_ktime_read_ndelays));
		WARN_ON_ONCE((i <= max_retries) !=
			     !(clocksource_wdtest_ktime.flags & CLOCK_SOURCE_UNSTABLE));
		wdtest_ktime_clocksource_reset();
	}

	/* Verify tsc-like stability with clock-value-fuzz error injection. */
	pr_info("--- Watchdog clock-value-fuzz error injection, expect clock skew and per-CPU mismatches.\n");
	WRITE_ONCE(wdtest_ktime_read_fuzz, true);
	schedule_timeout_uninterruptible(2 * HZ);
	WARN_ON_ONCE(!(clocksource_wdtest_ktime.flags & CLOCK_SOURCE_UNSTABLE));
	clocksource_verify_percpu(&clocksource_wdtest_ktime);
	WRITE_ONCE(wdtest_ktime_read_fuzz, false);

	clocksource_unregister(&clocksource_wdtest_ktime);

	pr_info("--- Done with test.\n");
	return 0;
}

static void wdtest_print_module_parms(void)
{
	pr_alert("--- holdoff=%d\n", holdoff);
}

/* Cleanup function. */
static void clocksource_wdtest_cleanup(void)
{
}

static int __init clocksource_wdtest_init(void)
{
	int ret = 0;

	wdtest_print_module_parms();

	/* Create watchdog-test task. */
	wdtest_task = kthread_run(wdtest_func, NULL, "wdtest");
	if (IS_ERR(wdtest_task)) {
		ret = PTR_ERR(wdtest_task);
		pr_warn("%s: Failed to create wdtest kthread.\n", __func__);
		wdtest_task = NULL;
		return ret;
	}

	return 0;
}

module_init(clocksource_wdtest_init);
module_exit(clocksource_wdtest_cleanup);