1 files changed, 201 insertions, 0 deletions
diff --git a/kernel/time/clocksource-wdtest.c b/kernel/time/clocksource-wdtest.c
new file mode 100644
index 000000000000..df922f49d171
--- /dev/null
+++ b/kernel/time/clocksource-wdtest.c
@@ -0,0 +1,201 @@
+// 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;
+	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);