xref: /openbmc/linux/arch/powerpc/kernel/watchdog.c (revision 6ab70300)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Watchdog support on powerpc systems.
4  *
5  * Copyright 2017, IBM Corporation.
6  *
7  * This uses code from arch/sparc/kernel/nmi.c and kernel/watchdog.c
8  */
9 
10 #define pr_fmt(fmt) "watchdog: " fmt
11 
12 #include <linux/kernel.h>
13 #include <linux/param.h>
14 #include <linux/init.h>
15 #include <linux/percpu.h>
16 #include <linux/cpu.h>
17 #include <linux/nmi.h>
18 #include <linux/module.h>
19 #include <linux/export.h>
20 #include <linux/kprobes.h>
21 #include <linux/hardirq.h>
22 #include <linux/reboot.h>
23 #include <linux/slab.h>
24 #include <linux/kdebug.h>
25 #include <linux/sched/debug.h>
26 #include <linux/delay.h>
27 #include <linux/processor.h>
28 #include <linux/smp.h>
29 
30 #include <asm/interrupt.h>
31 #include <asm/paca.h>
32 #include <asm/nmi.h>
33 
34 /*
35  * The powerpc watchdog ensures that each CPU is able to service timers.
36  * The watchdog sets up a simple timer on each CPU to run once per timer
37  * period, and updates a per-cpu timestamp and a "pending" cpumask. This is
38  * the heartbeat.
39  *
40  * Then there are two systems to check that the heartbeat is still running.
41  * The local soft-NMI, and the SMP checker.
42  *
43  * The soft-NMI checker can detect lockups on the local CPU. When interrupts
44  * are disabled with local_irq_disable(), platforms that use soft-masking
45  * can leave hardware interrupts enabled and handle them with a masked
46  * interrupt handler. The masked handler can send the timer interrupt to the
47  * watchdog's soft_nmi_interrupt(), which appears to Linux as an NMI
48  * interrupt, and can be used to detect CPUs stuck with IRQs disabled.
49  *
50  * The soft-NMI checker will compare the heartbeat timestamp for this CPU
51  * with the current time, and take action if the difference exceeds the
52  * watchdog threshold.
53  *
54  * The limitation of the soft-NMI watchdog is that it does not work when
55  * interrupts are hard disabled or otherwise not being serviced. This is
56  * solved by also having a SMP watchdog where all CPUs check all other
57  * CPUs heartbeat.
58  *
59  * The SMP checker can detect lockups on other CPUs. A gobal "pending"
60  * cpumask is kept, containing all CPUs which enable the watchdog. Each
61  * CPU clears their pending bit in their heartbeat timer. When the bitmask
62  * becomes empty, the last CPU to clear its pending bit updates a global
63  * timestamp and refills the pending bitmask.
64  *
65  * In the heartbeat timer, if any CPU notices that the global timestamp has
66  * not been updated for a period exceeding the watchdog threshold, then it
67  * means the CPU(s) with their bit still set in the pending mask have had
68  * their heartbeat stop, and action is taken.
69  *
70  * Some platforms implement true NMI IPIs, which can be used by the SMP
71  * watchdog to detect an unresponsive CPU and pull it out of its stuck
72  * state with the NMI IPI, to get crash/debug data from it. This way the
73  * SMP watchdog can detect hardware interrupts off lockups.
74  */
75 
76 static cpumask_t wd_cpus_enabled __read_mostly;
77 
78 static u64 wd_panic_timeout_tb __read_mostly; /* timebase ticks until panic */
79 static u64 wd_smp_panic_timeout_tb __read_mostly; /* panic other CPUs */
80 
81 static u64 wd_timer_period_ms __read_mostly;  /* interval between heartbeat */
82 
83 static DEFINE_PER_CPU(struct hrtimer, wd_hrtimer);
84 static DEFINE_PER_CPU(u64, wd_timer_tb);
85 
86 /* SMP checker bits */
87 static unsigned long __wd_smp_lock;
88 static cpumask_t wd_smp_cpus_pending;
89 static cpumask_t wd_smp_cpus_stuck;
90 static u64 wd_smp_last_reset_tb;
91 
92 static inline void wd_smp_lock(unsigned long *flags)
93 {
94 	/*
95 	 * Avoid locking layers if possible.
96 	 * This may be called from low level interrupt handlers at some
97 	 * point in future.
98 	 */
99 	raw_local_irq_save(*flags);
100 	hard_irq_disable(); /* Make it soft-NMI safe */
101 	while (unlikely(test_and_set_bit_lock(0, &__wd_smp_lock))) {
102 		raw_local_irq_restore(*flags);
103 		spin_until_cond(!test_bit(0, &__wd_smp_lock));
104 		raw_local_irq_save(*flags);
105 		hard_irq_disable();
106 	}
107 }
108 
109 static inline void wd_smp_unlock(unsigned long *flags)
110 {
111 	clear_bit_unlock(0, &__wd_smp_lock);
112 	raw_local_irq_restore(*flags);
113 }
114 
115 static void wd_lockup_ipi(struct pt_regs *regs)
116 {
117 	int cpu = raw_smp_processor_id();
118 	u64 tb = get_tb();
119 
120 	pr_emerg("CPU %d Hard LOCKUP\n", cpu);
121 	pr_emerg("CPU %d TB:%lld, last heartbeat TB:%lld (%lldms ago)\n",
122 		 cpu, tb, per_cpu(wd_timer_tb, cpu),
123 		 tb_to_ns(tb - per_cpu(wd_timer_tb, cpu)) / 1000000);
124 	print_modules();
125 	print_irqtrace_events(current);
126 	if (regs)
127 		show_regs(regs);
128 	else
129 		dump_stack();
130 
131 	/* Do not panic from here because that can recurse into NMI IPI layer */
132 }
133 
134 static void set_cpumask_stuck(const struct cpumask *cpumask, u64 tb)
135 {
136 	cpumask_or(&wd_smp_cpus_stuck, &wd_smp_cpus_stuck, cpumask);
137 	cpumask_andnot(&wd_smp_cpus_pending, &wd_smp_cpus_pending, cpumask);
138 	if (cpumask_empty(&wd_smp_cpus_pending)) {
139 		wd_smp_last_reset_tb = tb;
140 		cpumask_andnot(&wd_smp_cpus_pending,
141 				&wd_cpus_enabled,
142 				&wd_smp_cpus_stuck);
143 	}
144 }
145 static void set_cpu_stuck(int cpu, u64 tb)
146 {
147 	set_cpumask_stuck(cpumask_of(cpu), tb);
148 }
149 
150 static void watchdog_smp_panic(int cpu, u64 tb)
151 {
152 	unsigned long flags;
153 	int c;
154 
155 	wd_smp_lock(&flags);
156 	/* Double check some things under lock */
157 	if ((s64)(tb - wd_smp_last_reset_tb) < (s64)wd_smp_panic_timeout_tb)
158 		goto out;
159 	if (cpumask_test_cpu(cpu, &wd_smp_cpus_pending))
160 		goto out;
161 	if (cpumask_weight(&wd_smp_cpus_pending) == 0)
162 		goto out;
163 
164 	pr_emerg("CPU %d detected hard LOCKUP on other CPUs %*pbl\n",
165 		 cpu, cpumask_pr_args(&wd_smp_cpus_pending));
166 	pr_emerg("CPU %d TB:%lld, last SMP heartbeat TB:%lld (%lldms ago)\n",
167 		 cpu, tb, wd_smp_last_reset_tb,
168 		 tb_to_ns(tb - wd_smp_last_reset_tb) / 1000000);
169 
170 	if (!sysctl_hardlockup_all_cpu_backtrace) {
171 		/*
172 		 * Try to trigger the stuck CPUs, unless we are going to
173 		 * get a backtrace on all of them anyway.
174 		 */
175 		for_each_cpu(c, &wd_smp_cpus_pending) {
176 			if (c == cpu)
177 				continue;
178 			smp_send_nmi_ipi(c, wd_lockup_ipi, 1000000);
179 		}
180 	}
181 
182 	/* Take the stuck CPUs out of the watch group */
183 	set_cpumask_stuck(&wd_smp_cpus_pending, tb);
184 
185 	wd_smp_unlock(&flags);
186 
187 	if (sysctl_hardlockup_all_cpu_backtrace)
188 		trigger_allbutself_cpu_backtrace();
189 
190 	/*
191 	 * Force flush any remote buffers that might be stuck in IRQ context
192 	 * and therefore could not run their irq_work.
193 	 */
194 	printk_trigger_flush();
195 
196 	if (hardlockup_panic)
197 		nmi_panic(NULL, "Hard LOCKUP");
198 
199 	return;
200 
201 out:
202 	wd_smp_unlock(&flags);
203 }
204 
205 static void wd_smp_clear_cpu_pending(int cpu, u64 tb)
206 {
207 	if (!cpumask_test_cpu(cpu, &wd_smp_cpus_pending)) {
208 		if (unlikely(cpumask_test_cpu(cpu, &wd_smp_cpus_stuck))) {
209 			struct pt_regs *regs = get_irq_regs();
210 			unsigned long flags;
211 
212 			wd_smp_lock(&flags);
213 
214 			pr_emerg("CPU %d became unstuck TB:%lld\n",
215 				 cpu, tb);
216 			print_irqtrace_events(current);
217 			if (regs)
218 				show_regs(regs);
219 			else
220 				dump_stack();
221 
222 			cpumask_clear_cpu(cpu, &wd_smp_cpus_stuck);
223 			wd_smp_unlock(&flags);
224 		}
225 		return;
226 	}
227 	cpumask_clear_cpu(cpu, &wd_smp_cpus_pending);
228 	if (cpumask_empty(&wd_smp_cpus_pending)) {
229 		unsigned long flags;
230 
231 		wd_smp_lock(&flags);
232 		if (cpumask_empty(&wd_smp_cpus_pending)) {
233 			wd_smp_last_reset_tb = tb;
234 			cpumask_andnot(&wd_smp_cpus_pending,
235 					&wd_cpus_enabled,
236 					&wd_smp_cpus_stuck);
237 		}
238 		wd_smp_unlock(&flags);
239 	}
240 }
241 
242 static void watchdog_timer_interrupt(int cpu)
243 {
244 	u64 tb = get_tb();
245 
246 	per_cpu(wd_timer_tb, cpu) = tb;
247 
248 	wd_smp_clear_cpu_pending(cpu, tb);
249 
250 	if ((s64)(tb - wd_smp_last_reset_tb) >= (s64)wd_smp_panic_timeout_tb)
251 		watchdog_smp_panic(cpu, tb);
252 }
253 
254 DEFINE_INTERRUPT_HANDLER_NMI(soft_nmi_interrupt)
255 {
256 	unsigned long flags;
257 	int cpu = raw_smp_processor_id();
258 	u64 tb;
259 
260 	/* should only arrive from kernel, with irqs disabled */
261 	WARN_ON_ONCE(!arch_irq_disabled_regs(regs));
262 
263 	if (!cpumask_test_cpu(cpu, &wd_cpus_enabled))
264 		return 0;
265 
266 	__this_cpu_inc(irq_stat.soft_nmi_irqs);
267 
268 	tb = get_tb();
269 	if (tb - per_cpu(wd_timer_tb, cpu) >= wd_panic_timeout_tb) {
270 		wd_smp_lock(&flags);
271 		if (cpumask_test_cpu(cpu, &wd_smp_cpus_stuck)) {
272 			wd_smp_unlock(&flags);
273 			return 0;
274 		}
275 		set_cpu_stuck(cpu, tb);
276 
277 		pr_emerg("CPU %d self-detected hard LOCKUP @ %pS\n",
278 			 cpu, (void *)regs->nip);
279 		pr_emerg("CPU %d TB:%lld, last heartbeat TB:%lld (%lldms ago)\n",
280 			 cpu, tb, per_cpu(wd_timer_tb, cpu),
281 			 tb_to_ns(tb - per_cpu(wd_timer_tb, cpu)) / 1000000);
282 		print_modules();
283 		print_irqtrace_events(current);
284 		show_regs(regs);
285 
286 		wd_smp_unlock(&flags);
287 
288 		if (sysctl_hardlockup_all_cpu_backtrace)
289 			trigger_allbutself_cpu_backtrace();
290 
291 		if (hardlockup_panic)
292 			nmi_panic(regs, "Hard LOCKUP");
293 	}
294 	if (wd_panic_timeout_tb < 0x7fffffff)
295 		mtspr(SPRN_DEC, wd_panic_timeout_tb);
296 
297 	return 0;
298 }
299 
300 static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
301 {
302 	int cpu = smp_processor_id();
303 
304 	if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
305 		return HRTIMER_NORESTART;
306 
307 	if (!cpumask_test_cpu(cpu, &watchdog_cpumask))
308 		return HRTIMER_NORESTART;
309 
310 	watchdog_timer_interrupt(cpu);
311 
312 	hrtimer_forward_now(hrtimer, ms_to_ktime(wd_timer_period_ms));
313 
314 	return HRTIMER_RESTART;
315 }
316 
317 void arch_touch_nmi_watchdog(void)
318 {
319 	unsigned long ticks = tb_ticks_per_usec * wd_timer_period_ms * 1000;
320 	int cpu = smp_processor_id();
321 	u64 tb = get_tb();
322 
323 	if (tb - per_cpu(wd_timer_tb, cpu) >= ticks) {
324 		per_cpu(wd_timer_tb, cpu) = tb;
325 		wd_smp_clear_cpu_pending(cpu, tb);
326 	}
327 }
328 EXPORT_SYMBOL(arch_touch_nmi_watchdog);
329 
330 static void start_watchdog(void *arg)
331 {
332 	struct hrtimer *hrtimer = this_cpu_ptr(&wd_hrtimer);
333 	int cpu = smp_processor_id();
334 	unsigned long flags;
335 
336 	if (cpumask_test_cpu(cpu, &wd_cpus_enabled)) {
337 		WARN_ON(1);
338 		return;
339 	}
340 
341 	if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
342 		return;
343 
344 	if (!cpumask_test_cpu(cpu, &watchdog_cpumask))
345 		return;
346 
347 	wd_smp_lock(&flags);
348 	cpumask_set_cpu(cpu, &wd_cpus_enabled);
349 	if (cpumask_weight(&wd_cpus_enabled) == 1) {
350 		cpumask_set_cpu(cpu, &wd_smp_cpus_pending);
351 		wd_smp_last_reset_tb = get_tb();
352 	}
353 	wd_smp_unlock(&flags);
354 
355 	*this_cpu_ptr(&wd_timer_tb) = get_tb();
356 
357 	hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
358 	hrtimer->function = watchdog_timer_fn;
359 	hrtimer_start(hrtimer, ms_to_ktime(wd_timer_period_ms),
360 		      HRTIMER_MODE_REL_PINNED);
361 }
362 
363 static int start_watchdog_on_cpu(unsigned int cpu)
364 {
365 	return smp_call_function_single(cpu, start_watchdog, NULL, true);
366 }
367 
368 static void stop_watchdog(void *arg)
369 {
370 	struct hrtimer *hrtimer = this_cpu_ptr(&wd_hrtimer);
371 	int cpu = smp_processor_id();
372 	unsigned long flags;
373 
374 	if (!cpumask_test_cpu(cpu, &wd_cpus_enabled))
375 		return; /* Can happen in CPU unplug case */
376 
377 	hrtimer_cancel(hrtimer);
378 
379 	wd_smp_lock(&flags);
380 	cpumask_clear_cpu(cpu, &wd_cpus_enabled);
381 	wd_smp_unlock(&flags);
382 
383 	wd_smp_clear_cpu_pending(cpu, get_tb());
384 }
385 
386 static int stop_watchdog_on_cpu(unsigned int cpu)
387 {
388 	return smp_call_function_single(cpu, stop_watchdog, NULL, true);
389 }
390 
391 static void watchdog_calc_timeouts(void)
392 {
393 	wd_panic_timeout_tb = watchdog_thresh * ppc_tb_freq;
394 
395 	/* Have the SMP detector trigger a bit later */
396 	wd_smp_panic_timeout_tb = wd_panic_timeout_tb * 3 / 2;
397 
398 	/* 2/5 is the factor that the perf based detector uses */
399 	wd_timer_period_ms = watchdog_thresh * 1000 * 2 / 5;
400 }
401 
402 void watchdog_nmi_stop(void)
403 {
404 	int cpu;
405 
406 	for_each_cpu(cpu, &wd_cpus_enabled)
407 		stop_watchdog_on_cpu(cpu);
408 }
409 
410 void watchdog_nmi_start(void)
411 {
412 	int cpu;
413 
414 	watchdog_calc_timeouts();
415 	for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask)
416 		start_watchdog_on_cpu(cpu);
417 }
418 
419 /*
420  * Invoked from core watchdog init.
421  */
422 int __init watchdog_nmi_probe(void)
423 {
424 	int err;
425 
426 	err = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
427 					"powerpc/watchdog:online",
428 					start_watchdog_on_cpu,
429 					stop_watchdog_on_cpu);
430 	if (err < 0) {
431 		pr_warn("could not be initialized");
432 		return err;
433 	}
434 	return 0;
435 }
436