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