1/*
  2 * Detect hard lockups on a system
  3 *
  4 * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
  5 *
  6 * Note: Most of this code is borrowed heavily from the original softlockup
  7 * detector, so thanks to Ingo for the initial implementation.
  8 * Some chunks also taken from the old x86-specific nmi watchdog code, thanks
  9 * to those contributors as well.
 10 */
 11
 12#define pr_fmt(fmt) "NMI watchdog: " fmt
 13
 14#include <linux/nmi.h>
 15#include <linux/module.h>
 16#include <asm/irq_regs.h>
 17#include <linux/perf_event.h>
 18
 19static DEFINE_PER_CPU(bool, hard_watchdog_warn);
 20static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
 21static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
 22
 23/* boot commands */
 24/*
 25 * Should we panic when a soft-lockup or hard-lockup occurs:
 26 */
 27unsigned int __read_mostly hardlockup_panic =
 28			CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
 29static unsigned long hardlockup_allcpu_dumped;
 30/*
 31 * We may not want to enable hard lockup detection by default in all cases,
 32 * for example when running the kernel as a guest on a hypervisor. In these
 33 * cases this function can be called to disable hard lockup detection. This
 34 * function should only be executed once by the boot processor before the
 35 * kernel command line parameters are parsed, because otherwise it is not
 36 * possible to override this in hardlockup_panic_setup().
 37 */
 38void hardlockup_detector_disable(void)
 39{
 40	watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
 41}
 42
 43static int __init hardlockup_panic_setup(char *str)
 44{
 45	if (!strncmp(str, "panic", 5))
 46		hardlockup_panic = 1;
 47	else if (!strncmp(str, "nopanic", 7))
 48		hardlockup_panic = 0;
 49	else if (!strncmp(str, "0", 1))
 50		watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
 51	else if (!strncmp(str, "1", 1))
 52		watchdog_enabled |= NMI_WATCHDOG_ENABLED;
 53	return 1;
 54}
 55__setup("nmi_watchdog=", hardlockup_panic_setup);
 56
 57void touch_nmi_watchdog(void)
 58{
 59	/*
 60	 * Using __raw here because some code paths have
 61	 * preemption enabled.  If preemption is enabled
 62	 * then interrupts should be enabled too, in which
 63	 * case we shouldn't have to worry about the watchdog
 64	 * going off.
 65	 */
 66	raw_cpu_write(watchdog_nmi_touch, true);
 67	touch_softlockup_watchdog();
 68}
 69EXPORT_SYMBOL(touch_nmi_watchdog);
 70
 71static struct perf_event_attr wd_hw_attr = {
 72	.type		= PERF_TYPE_HARDWARE,
 73	.config		= PERF_COUNT_HW_CPU_CYCLES,
 74	.size		= sizeof(struct perf_event_attr),
 75	.pinned		= 1,
 76	.disabled	= 1,
 77};
 78
 79/* Callback function for perf event subsystem */
 80static void watchdog_overflow_callback(struct perf_event *event,
 81		 struct perf_sample_data *data,
 82		 struct pt_regs *regs)
 83{
 84	/* Ensure the watchdog never gets throttled */
 85	event->hw.interrupts = 0;
 86
 87	if (atomic_read(&watchdog_park_in_progress) != 0)
 88		return;
 89
 90	if (__this_cpu_read(watchdog_nmi_touch) == true) {
 91		__this_cpu_write(watchdog_nmi_touch, false);
 92		return;
 93	}
 94
 95	/* check for a hardlockup
 96	 * This is done by making sure our timer interrupt
 97	 * is incrementing.  The timer interrupt should have
 98	 * fired multiple times before we overflow'd.  If it hasn't
 99	 * then this is a good indication the cpu is stuck
100	 */
101	if (is_hardlockup()) {
102		int this_cpu = smp_processor_id();
103
104		/* only print hardlockups once */
105		if (__this_cpu_read(hard_watchdog_warn) == true)
106			return;
107
108		pr_emerg("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
109		print_modules();
110		print_irqtrace_events(current);
111		if (regs)
112			show_regs(regs);
113		else
114			dump_stack();
115
116		/*
117		 * Perform all-CPU dump only once to avoid multiple hardlockups
118		 * generating interleaving traces
119		 */
120		if (sysctl_hardlockup_all_cpu_backtrace &&
121				!test_and_set_bit(0, &hardlockup_allcpu_dumped))
122			trigger_allbutself_cpu_backtrace();
123
124		if (hardlockup_panic)
125			nmi_panic(regs, "Hard LOCKUP");
126
127		__this_cpu_write(hard_watchdog_warn, true);
128		return;
129	}
130
131	__this_cpu_write(hard_watchdog_warn, false);
132	return;
133}
134
135/*
136 * People like the simple clean cpu node info on boot.
137 * Reduce the watchdog noise by only printing messages
138 * that are different from what cpu0 displayed.
139 */
140static unsigned long cpu0_err;
141
142int watchdog_nmi_enable(unsigned int cpu)
143{
144	struct perf_event_attr *wd_attr;
145	struct perf_event *event = per_cpu(watchdog_ev, cpu);
146
147	/* nothing to do if the hard lockup detector is disabled */
148	if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
149		goto out;
150
151	/* is it already setup and enabled? */
152	if (event && event->state > PERF_EVENT_STATE_OFF)
153		goto out;
154
155	/* it is setup but not enabled */
156	if (event != NULL)
157		goto out_enable;
158
159	wd_attr = &wd_hw_attr;
160	wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
161
162	/* Try to register using hardware perf events */
163	event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL);
164
165	/* save cpu0 error for future comparision */
166	if (cpu == 0 && IS_ERR(event))
167		cpu0_err = PTR_ERR(event);
168
169	if (!IS_ERR(event)) {
170		/* only print for cpu0 or different than cpu0 */
171		if (cpu == 0 || cpu0_err)
172			pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.\n");
173		goto out_save;
174	}
175
176	/*
177	 * Disable the hard lockup detector if _any_ CPU fails to set up
178	 * set up the hardware perf event. The watchdog() function checks
179	 * the NMI_WATCHDOG_ENABLED bit periodically.
180	 *
181	 * The barriers are for syncing up watchdog_enabled across all the
182	 * cpus, as clear_bit() does not use barriers.
183	 */
184	smp_mb__before_atomic();
185	clear_bit(NMI_WATCHDOG_ENABLED_BIT, &watchdog_enabled);
186	smp_mb__after_atomic();
187
188	/* skip displaying the same error again */
189	if (cpu > 0 && (PTR_ERR(event) == cpu0_err))
190		return PTR_ERR(event);
191
192	/* vary the KERN level based on the returned errno */
193	if (PTR_ERR(event) == -EOPNOTSUPP)
194		pr_info("disabled (cpu%i): not supported (no LAPIC?)\n", cpu);
195	else if (PTR_ERR(event) == -ENOENT)
196		pr_warn("disabled (cpu%i): hardware events not enabled\n",
197			 cpu);
198	else
199		pr_err("disabled (cpu%i): unable to create perf event: %ld\n",
200			cpu, PTR_ERR(event));
201
202	pr_info("Shutting down hard lockup detector on all cpus\n");
203
204	return PTR_ERR(event);
205
206	/* success path */
207out_save:
208	per_cpu(watchdog_ev, cpu) = event;
209out_enable:
210	perf_event_enable(per_cpu(watchdog_ev, cpu));
211out:
212	return 0;
213}
214
215void watchdog_nmi_disable(unsigned int cpu)
216{
217	struct perf_event *event = per_cpu(watchdog_ev, cpu);
218
219	if (event) {
220		perf_event_disable(event);
221		per_cpu(watchdog_ev, cpu) = NULL;
222
223		/* should be in cleanup, but blocks oprofile */
224		perf_event_release_kernel(event);
225	}
226	if (cpu == 0) {
227		/* watchdog_nmi_enable() expects this to be zero initially. */
228		cpu0_err = 0;
229	}
230}