kernel/time/clocksource-wdtest.c

   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
  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
  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
  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. */
  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. */
 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
 172 static void wdtest_print_module_parms(void)
 173 {
 174         pr_alert("--- holdoff=%d\n", holdoff);
 175 }
 176
 177 /* Cleanup function. */
 178 static void clocksource_wdtest_cleanup(void)
 179 {
 180 }
 181
 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);