1 // SPDX-License-Identifier: GPL-2.0+
2 /*
3 * Unit test for the clocksource watchdog.
4 *
5 * Copyright (C) 2021 Facebook, Inc.
6 *
7 * Author: Paul E. McKenney <paulmck@kernel.org>
8 */
9 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
10
11 #include <linux/device.h>
12 #include <linux/clocksource.h>
13 #include <linux/init.h>
14 #include <linux/module.h>
15 #include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
16 #include <linux/tick.h>
17 #include <linux/kthread.h>
18 #include <linux/delay.h>
19 #include <linux/prandom.h>
20 #include <linux/cpu.h>
21
22 #include "tick-internal.h"
23
24 MODULE_LICENSE("GPL");
25 MODULE_AUTHOR("Paul E. McKenney <paulmck@kernel.org>");
26
27 static int holdoff = IS_BUILTIN(CONFIG_TEST_CLOCKSOURCE_WATCHDOG) ? 10 : 0;
28 module_param(holdoff, int, 0444);
29 MODULE_PARM_DESC(holdoff, "Time to wait to start test (s).");
30
31 /* Watchdog kthread's task_struct pointer for debug purposes. */
32 static struct task_struct *wdtest_task;
33
wdtest_jiffies_read(struct clocksource * cs)34 static u64 wdtest_jiffies_read(struct clocksource *cs)
35 {
36 return (u64)jiffies;
37 }
38
39 static struct clocksource clocksource_wdtest_jiffies = {
40 .name = "wdtest-jiffies",
41 .rating = 1, /* lowest valid rating*/
42 .uncertainty_margin = TICK_NSEC,
43 .read = wdtest_jiffies_read,
44 .mask = CLOCKSOURCE_MASK(32),
45 .flags = CLOCK_SOURCE_MUST_VERIFY,
46 .mult = TICK_NSEC << JIFFIES_SHIFT, /* details above */
47 .shift = JIFFIES_SHIFT,
48 .max_cycles = 10,
49 };
50
51 static int wdtest_ktime_read_ndelays;
52 static bool wdtest_ktime_read_fuzz;
53
wdtest_ktime_read(struct clocksource * cs)54 static u64 wdtest_ktime_read(struct clocksource *cs)
55 {
56 int wkrn = READ_ONCE(wdtest_ktime_read_ndelays);
57 static int sign = 1;
58 u64 ret;
59
60 if (wkrn) {
61 udelay(cs->uncertainty_margin / 250);
62 WRITE_ONCE(wdtest_ktime_read_ndelays, wkrn - 1);
63 }
64 ret = ktime_get_real_fast_ns();
65 if (READ_ONCE(wdtest_ktime_read_fuzz)) {
66 sign = -sign;
67 ret = ret + sign * 100 * NSEC_PER_MSEC;
68 }
69 return ret;
70 }
71
wdtest_ktime_cs_mark_unstable(struct clocksource * cs)72 static void wdtest_ktime_cs_mark_unstable(struct clocksource *cs)
73 {
74 pr_info("--- Marking %s unstable due to clocksource watchdog.\n", cs->name);
75 }
76
77 #define KTIME_FLAGS (CLOCK_SOURCE_IS_CONTINUOUS | \
78 CLOCK_SOURCE_VALID_FOR_HRES | \
79 CLOCK_SOURCE_MUST_VERIFY | \
80 CLOCK_SOURCE_VERIFY_PERCPU)
81
82 static struct clocksource clocksource_wdtest_ktime = {
83 .name = "wdtest-ktime",
84 .rating = 300,
85 .read = wdtest_ktime_read,
86 .mask = CLOCKSOURCE_MASK(64),
87 .flags = KTIME_FLAGS,
88 .mark_unstable = wdtest_ktime_cs_mark_unstable,
89 .list = LIST_HEAD_INIT(clocksource_wdtest_ktime.list),
90 };
91
92 /* Reset the clocksource if needed. */
wdtest_ktime_clocksource_reset(void)93 static void wdtest_ktime_clocksource_reset(void)
94 {
95 if (clocksource_wdtest_ktime.flags & CLOCK_SOURCE_UNSTABLE) {
96 clocksource_unregister(&clocksource_wdtest_ktime);
97 clocksource_wdtest_ktime.flags = KTIME_FLAGS;
98 schedule_timeout_uninterruptible(HZ / 10);
99 clocksource_register_khz(&clocksource_wdtest_ktime, 1000 * 1000);
100 }
101 }
102
103 /* Run the specified series of watchdog tests. */
wdtest_func(void * arg)104 static int wdtest_func(void *arg)
105 {
106 unsigned long j1, j2;
107 char *s;
108 int i;
109
110 schedule_timeout_uninterruptible(holdoff * HZ);
111
112 /*
113 * Verify that jiffies-like clocksources get the manually
114 * specified uncertainty margin.
115 */
116 pr_info("--- Verify jiffies-like uncertainty margin.\n");
117 __clocksource_register(&clocksource_wdtest_jiffies);
118 WARN_ON_ONCE(clocksource_wdtest_jiffies.uncertainty_margin != TICK_NSEC);
119
120 j1 = clocksource_wdtest_jiffies.read(&clocksource_wdtest_jiffies);
121 schedule_timeout_uninterruptible(HZ);
122 j2 = clocksource_wdtest_jiffies.read(&clocksource_wdtest_jiffies);
123 WARN_ON_ONCE(j1 == j2);
124
125 clocksource_unregister(&clocksource_wdtest_jiffies);
126
127 /*
128 * Verify that tsc-like clocksources are assigned a reasonable
129 * uncertainty margin.
130 */
131 pr_info("--- Verify tsc-like uncertainty margin.\n");
132 clocksource_register_khz(&clocksource_wdtest_ktime, 1000 * 1000);
133 WARN_ON_ONCE(clocksource_wdtest_ktime.uncertainty_margin < NSEC_PER_USEC);
134
135 j1 = clocksource_wdtest_ktime.read(&clocksource_wdtest_ktime);
136 udelay(1);
137 j2 = clocksource_wdtest_ktime.read(&clocksource_wdtest_ktime);
138 pr_info("--- tsc-like times: %lu - %lu = %lu.\n", j2, j1, j2 - j1);
139 WARN_ON_ONCE(time_before(j2, j1 + NSEC_PER_USEC));
140
141 /* Verify tsc-like stability with various numbers of errors injected. */
142 for (i = 0; i <= max_cswd_read_retries + 1; i++) {
143 if (i <= 1 && i < max_cswd_read_retries)
144 s = "";
145 else if (i <= max_cswd_read_retries)
146 s = ", expect message";
147 else
148 s = ", expect clock skew";
149 pr_info("--- Watchdog with %dx error injection, %lu retries%s.\n", i, max_cswd_read_retries, s);
150 WRITE_ONCE(wdtest_ktime_read_ndelays, i);
151 schedule_timeout_uninterruptible(2 * HZ);
152 WARN_ON_ONCE(READ_ONCE(wdtest_ktime_read_ndelays));
153 WARN_ON_ONCE((i <= max_cswd_read_retries) !=
154 !(clocksource_wdtest_ktime.flags & CLOCK_SOURCE_UNSTABLE));
155 wdtest_ktime_clocksource_reset();
156 }
157
158 /* Verify tsc-like stability with clock-value-fuzz error injection. */
159 pr_info("--- Watchdog clock-value-fuzz error injection, expect clock skew and per-CPU mismatches.\n");
160 WRITE_ONCE(wdtest_ktime_read_fuzz, true);
161 schedule_timeout_uninterruptible(2 * HZ);
162 WARN_ON_ONCE(!(clocksource_wdtest_ktime.flags & CLOCK_SOURCE_UNSTABLE));
163 clocksource_verify_percpu(&clocksource_wdtest_ktime);
164 WRITE_ONCE(wdtest_ktime_read_fuzz, false);
165
166 clocksource_unregister(&clocksource_wdtest_ktime);
167
168 pr_info("--- Done with test.\n");
169 return 0;
170 }
171
wdtest_print_module_parms(void)172 static void wdtest_print_module_parms(void)
173 {
174 pr_alert("--- holdoff=%d\n", holdoff);
175 }
176
177 /* Cleanup function. */
clocksource_wdtest_cleanup(void)178 static void clocksource_wdtest_cleanup(void)
179 {
180 }
181
clocksource_wdtest_init(void)182 static int __init clocksource_wdtest_init(void)
183 {
184 int ret = 0;
185
186 wdtest_print_module_parms();
187
188 /* Create watchdog-test task. */
189 wdtest_task = kthread_run(wdtest_func, NULL, "wdtest");
190 if (IS_ERR(wdtest_task)) {
191 ret = PTR_ERR(wdtest_task);
192 pr_warn("%s: Failed to create wdtest kthread.\n", __func__);
193 wdtest_task = NULL;
194 return ret;
195 }
196
197 return 0;
198 }
199
200 module_init(clocksource_wdtest_init);
201 module_exit(clocksource_wdtest_cleanup);
202
