diff options
Diffstat (limited to 'kernel/time/clocksource-wdtest.c')
| -rw-r--r-- | kernel/time/clocksource-wdtest.c | 202 |
1 files changed, 202 insertions, 0 deletions
diff --git a/kernel/time/clocksource-wdtest.c b/kernel/time/clocksource-wdtest.c new file mode 100644 index 000000000000..01df12395c0e --- /dev/null +++ b/kernel/time/clocksource-wdtest.c @@ -0,0 +1,202 @@ +// 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> + +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; +} + +/* Assume HZ > 100. */ +#define JIFFIES_SHIFT 8 + +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; + char *s; + int i; + + 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. */ + for (i = 0; i <= max_cswd_read_retries + 1; i++) { + if (i <= 1 && i < max_cswd_read_retries) + s = ""; + else if (i <= max_cswd_read_retries) + s = ", expect message"; + else + s = ", expect clock skew"; + pr_info("--- Watchdog with %dx error injection, %lu retries%s.\n", i, max_cswd_read_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_cswd_read_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); |