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![Paul E. McKenney](/assets/img/avatar_default.png)
The clocksource watchdog test sets a local JIFFIES_SHIFT macro and assumes that HZ is >= 100. For smaller HZ values this shift value is too large and causes undefined behaviour. Move the HZ-based definitions of JIFFIES_SHIFT from kernel/time/jiffies.c to kernel/time/tick-internal.h so the clocksource watchdog test can utilize them, which makes it work correctly with all HZ values. [ tglx: Resolved conflicts and massaged changelog ] Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/lkml/20210812000133.GA402890@paulmck-ThinkPad-P17-Gen-1/
201 lines
5.8 KiB
C
201 lines
5.8 KiB
C
// SPDX-License-Identifier: GPL-2.0+
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/*
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* Unit test for the clocksource watchdog.
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*
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* Copyright (C) 2021 Facebook, Inc.
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*
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* Author: Paul E. McKenney <paulmck@kernel.org>
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/device.h>
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#include <linux/clocksource.h>
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#include <linux/init.h>
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#include <linux/module.h>
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#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
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#include <linux/tick.h>
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#include <linux/kthread.h>
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#include <linux/delay.h>
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#include <linux/prandom.h>
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#include <linux/cpu.h>
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#include "tick-internal.h"
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Paul E. McKenney <paulmck@kernel.org>");
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static int holdoff = IS_BUILTIN(CONFIG_TEST_CLOCKSOURCE_WATCHDOG) ? 10 : 0;
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module_param(holdoff, int, 0444);
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MODULE_PARM_DESC(holdoff, "Time to wait to start test (s).");
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/* Watchdog kthread's task_struct pointer for debug purposes. */
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static struct task_struct *wdtest_task;
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static u64 wdtest_jiffies_read(struct clocksource *cs)
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{
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return (u64)jiffies;
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}
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static struct clocksource clocksource_wdtest_jiffies = {
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.name = "wdtest-jiffies",
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.rating = 1, /* lowest valid rating*/
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.uncertainty_margin = TICK_NSEC,
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.read = wdtest_jiffies_read,
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.mask = CLOCKSOURCE_MASK(32),
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.flags = CLOCK_SOURCE_MUST_VERIFY,
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.mult = TICK_NSEC << JIFFIES_SHIFT, /* details above */
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.shift = JIFFIES_SHIFT,
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.max_cycles = 10,
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};
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static int wdtest_ktime_read_ndelays;
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static bool wdtest_ktime_read_fuzz;
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static u64 wdtest_ktime_read(struct clocksource *cs)
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{
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int wkrn = READ_ONCE(wdtest_ktime_read_ndelays);
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static int sign = 1;
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u64 ret;
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if (wkrn) {
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udelay(cs->uncertainty_margin / 250);
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WRITE_ONCE(wdtest_ktime_read_ndelays, wkrn - 1);
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}
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ret = ktime_get_real_fast_ns();
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if (READ_ONCE(wdtest_ktime_read_fuzz)) {
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sign = -sign;
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ret = ret + sign * 100 * NSEC_PER_MSEC;
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}
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return ret;
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}
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static void wdtest_ktime_cs_mark_unstable(struct clocksource *cs)
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{
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pr_info("--- Marking %s unstable due to clocksource watchdog.\n", cs->name);
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}
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#define KTIME_FLAGS (CLOCK_SOURCE_IS_CONTINUOUS | \
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CLOCK_SOURCE_VALID_FOR_HRES | \
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CLOCK_SOURCE_MUST_VERIFY | \
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CLOCK_SOURCE_VERIFY_PERCPU)
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static struct clocksource clocksource_wdtest_ktime = {
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.name = "wdtest-ktime",
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.rating = 300,
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.read = wdtest_ktime_read,
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.mask = CLOCKSOURCE_MASK(64),
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.flags = KTIME_FLAGS,
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.mark_unstable = wdtest_ktime_cs_mark_unstable,
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.list = LIST_HEAD_INIT(clocksource_wdtest_ktime.list),
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};
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/* Reset the clocksource if needed. */
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static void wdtest_ktime_clocksource_reset(void)
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{
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if (clocksource_wdtest_ktime.flags & CLOCK_SOURCE_UNSTABLE) {
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clocksource_unregister(&clocksource_wdtest_ktime);
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clocksource_wdtest_ktime.flags = KTIME_FLAGS;
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schedule_timeout_uninterruptible(HZ / 10);
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clocksource_register_khz(&clocksource_wdtest_ktime, 1000 * 1000);
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}
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}
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/* Run the specified series of watchdog tests. */
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static int wdtest_func(void *arg)
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{
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unsigned long j1, j2;
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char *s;
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int i;
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schedule_timeout_uninterruptible(holdoff * HZ);
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/*
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* Verify that jiffies-like clocksources get the manually
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* specified uncertainty margin.
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*/
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pr_info("--- Verify jiffies-like uncertainty margin.\n");
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__clocksource_register(&clocksource_wdtest_jiffies);
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WARN_ON_ONCE(clocksource_wdtest_jiffies.uncertainty_margin != TICK_NSEC);
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j1 = clocksource_wdtest_jiffies.read(&clocksource_wdtest_jiffies);
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schedule_timeout_uninterruptible(HZ);
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j2 = clocksource_wdtest_jiffies.read(&clocksource_wdtest_jiffies);
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WARN_ON_ONCE(j1 == j2);
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clocksource_unregister(&clocksource_wdtest_jiffies);
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/*
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* Verify that tsc-like clocksources are assigned a reasonable
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* uncertainty margin.
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*/
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pr_info("--- Verify tsc-like uncertainty margin.\n");
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clocksource_register_khz(&clocksource_wdtest_ktime, 1000 * 1000);
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WARN_ON_ONCE(clocksource_wdtest_ktime.uncertainty_margin < NSEC_PER_USEC);
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j1 = clocksource_wdtest_ktime.read(&clocksource_wdtest_ktime);
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udelay(1);
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j2 = clocksource_wdtest_ktime.read(&clocksource_wdtest_ktime);
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pr_info("--- tsc-like times: %lu - %lu = %lu.\n", j2, j1, j2 - j1);
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WARN_ON_ONCE(time_before(j2, j1 + NSEC_PER_USEC));
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/* Verify tsc-like stability with various numbers of errors injected. */
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for (i = 0; i <= max_cswd_read_retries + 1; i++) {
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if (i <= 1 && i < max_cswd_read_retries)
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s = "";
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else if (i <= max_cswd_read_retries)
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s = ", expect message";
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else
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s = ", expect clock skew";
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pr_info("--- Watchdog with %dx error injection, %lu retries%s.\n", i, max_cswd_read_retries, s);
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WRITE_ONCE(wdtest_ktime_read_ndelays, i);
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schedule_timeout_uninterruptible(2 * HZ);
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WARN_ON_ONCE(READ_ONCE(wdtest_ktime_read_ndelays));
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WARN_ON_ONCE((i <= max_cswd_read_retries) !=
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!(clocksource_wdtest_ktime.flags & CLOCK_SOURCE_UNSTABLE));
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wdtest_ktime_clocksource_reset();
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}
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/* Verify tsc-like stability with clock-value-fuzz error injection. */
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pr_info("--- Watchdog clock-value-fuzz error injection, expect clock skew and per-CPU mismatches.\n");
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WRITE_ONCE(wdtest_ktime_read_fuzz, true);
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schedule_timeout_uninterruptible(2 * HZ);
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WARN_ON_ONCE(!(clocksource_wdtest_ktime.flags & CLOCK_SOURCE_UNSTABLE));
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clocksource_verify_percpu(&clocksource_wdtest_ktime);
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WRITE_ONCE(wdtest_ktime_read_fuzz, false);
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clocksource_unregister(&clocksource_wdtest_ktime);
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pr_info("--- Done with test.\n");
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return 0;
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}
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static void wdtest_print_module_parms(void)
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{
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pr_alert("--- holdoff=%d\n", holdoff);
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}
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/* Cleanup function. */
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static void clocksource_wdtest_cleanup(void)
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{
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}
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static int __init clocksource_wdtest_init(void)
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{
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int ret = 0;
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wdtest_print_module_parms();
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/* Create watchdog-test task. */
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wdtest_task = kthread_run(wdtest_func, NULL, "wdtest");
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if (IS_ERR(wdtest_task)) {
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ret = PTR_ERR(wdtest_task);
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pr_warn("%s: Failed to create wdtest kthread.\n", __func__);
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wdtest_task = NULL;
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return ret;
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}
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return 0;
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}
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module_init(clocksource_wdtest_init);
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module_exit(clocksource_wdtest_cleanup);
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