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 if (hardlockup_panic) 191 nmi_panic(NULL, "Hard LOCKUP"); 192 193 return; 194 195 out: 196 wd_smp_unlock(&flags); 197 } 198 199 static void wd_smp_clear_cpu_pending(int cpu, u64 tb) 200 { 201 if (!cpumask_test_cpu(cpu, &wd_smp_cpus_pending)) { 202 if (unlikely(cpumask_test_cpu(cpu, &wd_smp_cpus_stuck))) { 203 struct pt_regs *regs = get_irq_regs(); 204 unsigned long flags; 205 206 wd_smp_lock(&flags); 207 208 pr_emerg("CPU %d became unstuck TB:%lld\n", 209 cpu, tb); 210 print_irqtrace_events(current); 211 if (regs) 212 show_regs(regs); 213 else 214 dump_stack(); 215 216 cpumask_clear_cpu(cpu, &wd_smp_cpus_stuck); 217 wd_smp_unlock(&flags); 218 } 219 return; 220 } 221 cpumask_clear_cpu(cpu, &wd_smp_cpus_pending); 222 if (cpumask_empty(&wd_smp_cpus_pending)) { 223 unsigned long flags; 224 225 wd_smp_lock(&flags); 226 if (cpumask_empty(&wd_smp_cpus_pending)) { 227 wd_smp_last_reset_tb = tb; 228 cpumask_andnot(&wd_smp_cpus_pending, 229 &wd_cpus_enabled, 230 &wd_smp_cpus_stuck); 231 } 232 wd_smp_unlock(&flags); 233 } 234 } 235 236 static void watchdog_timer_interrupt(int cpu) 237 { 238 u64 tb = get_tb(); 239 240 per_cpu(wd_timer_tb, cpu) = tb; 241 242 wd_smp_clear_cpu_pending(cpu, tb); 243 244 if ((s64)(tb - wd_smp_last_reset_tb) >= (s64)wd_smp_panic_timeout_tb) 245 watchdog_smp_panic(cpu, tb); 246 } 247 248 DEFINE_INTERRUPT_HANDLER_NMI(soft_nmi_interrupt) 249 { 250 unsigned long flags; 251 int cpu = raw_smp_processor_id(); 252 u64 tb; 253 254 /* should only arrive from kernel, with irqs disabled */ 255 WARN_ON_ONCE(!arch_irq_disabled_regs(regs)); 256 257 if (!cpumask_test_cpu(cpu, &wd_cpus_enabled)) 258 return 0; 259 260 __this_cpu_inc(irq_stat.soft_nmi_irqs); 261 262 tb = get_tb(); 263 if (tb - per_cpu(wd_timer_tb, cpu) >= wd_panic_timeout_tb) { 264 wd_smp_lock(&flags); 265 if (cpumask_test_cpu(cpu, &wd_smp_cpus_stuck)) { 266 wd_smp_unlock(&flags); 267 return 0; 268 } 269 set_cpu_stuck(cpu, tb); 270 271 pr_emerg("CPU %d self-detected hard LOCKUP @ %pS\n", 272 cpu, (void *)regs->nip); 273 pr_emerg("CPU %d TB:%lld, last heartbeat TB:%lld (%lldms ago)\n", 274 cpu, tb, per_cpu(wd_timer_tb, cpu), 275 tb_to_ns(tb - per_cpu(wd_timer_tb, cpu)) / 1000000); 276 print_modules(); 277 print_irqtrace_events(current); 278 show_regs(regs); 279 280 wd_smp_unlock(&flags); 281 282 if (sysctl_hardlockup_all_cpu_backtrace) 283 trigger_allbutself_cpu_backtrace(); 284 285 if (hardlockup_panic) 286 nmi_panic(regs, "Hard LOCKUP"); 287 } 288 if (wd_panic_timeout_tb < 0x7fffffff) 289 mtspr(SPRN_DEC, wd_panic_timeout_tb); 290 291 return 0; 292 } 293 294 static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) 295 { 296 int cpu = smp_processor_id(); 297 298 if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED)) 299 return HRTIMER_NORESTART; 300 301 if (!cpumask_test_cpu(cpu, &watchdog_cpumask)) 302 return HRTIMER_NORESTART; 303 304 watchdog_timer_interrupt(cpu); 305 306 hrtimer_forward_now(hrtimer, ms_to_ktime(wd_timer_period_ms)); 307 308 return HRTIMER_RESTART; 309 } 310 311 void arch_touch_nmi_watchdog(void) 312 { 313 unsigned long ticks = tb_ticks_per_usec * wd_timer_period_ms * 1000; 314 int cpu = smp_processor_id(); 315 u64 tb = get_tb(); 316 317 if (tb - per_cpu(wd_timer_tb, cpu) >= ticks) { 318 per_cpu(wd_timer_tb, cpu) = tb; 319 wd_smp_clear_cpu_pending(cpu, tb); 320 } 321 } 322 EXPORT_SYMBOL(arch_touch_nmi_watchdog); 323 324 static void start_watchdog(void *arg) 325 { 326 struct hrtimer *hrtimer = this_cpu_ptr(&wd_hrtimer); 327 int cpu = smp_processor_id(); 328 unsigned long flags; 329 330 if (cpumask_test_cpu(cpu, &wd_cpus_enabled)) { 331 WARN_ON(1); 332 return; 333 } 334 335 if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED)) 336 return; 337 338 if (!cpumask_test_cpu(cpu, &watchdog_cpumask)) 339 return; 340 341 wd_smp_lock(&flags); 342 cpumask_set_cpu(cpu, &wd_cpus_enabled); 343 if (cpumask_weight(&wd_cpus_enabled) == 1) { 344 cpumask_set_cpu(cpu, &wd_smp_cpus_pending); 345 wd_smp_last_reset_tb = get_tb(); 346 } 347 wd_smp_unlock(&flags); 348 349 *this_cpu_ptr(&wd_timer_tb) = get_tb(); 350 351 hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); 352 hrtimer->function = watchdog_timer_fn; 353 hrtimer_start(hrtimer, ms_to_ktime(wd_timer_period_ms), 354 HRTIMER_MODE_REL_PINNED); 355 } 356 357 static int start_watchdog_on_cpu(unsigned int cpu) 358 { 359 return smp_call_function_single(cpu, start_watchdog, NULL, true); 360 } 361 362 static void stop_watchdog(void *arg) 363 { 364 struct hrtimer *hrtimer = this_cpu_ptr(&wd_hrtimer); 365 int cpu = smp_processor_id(); 366 unsigned long flags; 367 368 if (!cpumask_test_cpu(cpu, &wd_cpus_enabled)) 369 return; /* Can happen in CPU unplug case */ 370 371 hrtimer_cancel(hrtimer); 372 373 wd_smp_lock(&flags); 374 cpumask_clear_cpu(cpu, &wd_cpus_enabled); 375 wd_smp_unlock(&flags); 376 377 wd_smp_clear_cpu_pending(cpu, get_tb()); 378 } 379 380 static int stop_watchdog_on_cpu(unsigned int cpu) 381 { 382 return smp_call_function_single(cpu, stop_watchdog, NULL, true); 383 } 384 385 static void watchdog_calc_timeouts(void) 386 { 387 wd_panic_timeout_tb = watchdog_thresh * ppc_tb_freq; 388 389 /* Have the SMP detector trigger a bit later */ 390 wd_smp_panic_timeout_tb = wd_panic_timeout_tb * 3 / 2; 391 392 /* 2/5 is the factor that the perf based detector uses */ 393 wd_timer_period_ms = watchdog_thresh * 1000 * 2 / 5; 394 } 395 396 void watchdog_nmi_stop(void) 397 { 398 int cpu; 399 400 for_each_cpu(cpu, &wd_cpus_enabled) 401 stop_watchdog_on_cpu(cpu); 402 } 403 404 void watchdog_nmi_start(void) 405 { 406 int cpu; 407 408 watchdog_calc_timeouts(); 409 for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask) 410 start_watchdog_on_cpu(cpu); 411 } 412 413 /* 414 * Invoked from core watchdog init. 415 */ 416 int __init watchdog_nmi_probe(void) 417 { 418 int err; 419 420 err = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, 421 "powerpc/watchdog:online", 422 start_watchdog_on_cpu, 423 stop_watchdog_on_cpu); 424 if (err < 0) { 425 pr_warn("could not be initialized"); 426 return err; 427 } 428 return 0; 429 } 430