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 printk_safe_flush(); 188 /* 189 * printk_safe_flush() seems to require another print 190 * before anything actually goes out to console. 191 */ 192 if (sysctl_hardlockup_all_cpu_backtrace) 193 trigger_allbutself_cpu_backtrace(); 194 195 if (hardlockup_panic) 196 nmi_panic(NULL, "Hard LOCKUP"); 197 198 return; 199 200 out: 201 wd_smp_unlock(&flags); 202 } 203 204 static void wd_smp_clear_cpu_pending(int cpu, u64 tb) 205 { 206 if (!cpumask_test_cpu(cpu, &wd_smp_cpus_pending)) { 207 if (unlikely(cpumask_test_cpu(cpu, &wd_smp_cpus_stuck))) { 208 struct pt_regs *regs = get_irq_regs(); 209 unsigned long flags; 210 211 wd_smp_lock(&flags); 212 213 pr_emerg("CPU %d became unstuck TB:%lld\n", 214 cpu, tb); 215 print_irqtrace_events(current); 216 if (regs) 217 show_regs(regs); 218 else 219 dump_stack(); 220 221 cpumask_clear_cpu(cpu, &wd_smp_cpus_stuck); 222 wd_smp_unlock(&flags); 223 } 224 return; 225 } 226 cpumask_clear_cpu(cpu, &wd_smp_cpus_pending); 227 if (cpumask_empty(&wd_smp_cpus_pending)) { 228 unsigned long flags; 229 230 wd_smp_lock(&flags); 231 if (cpumask_empty(&wd_smp_cpus_pending)) { 232 wd_smp_last_reset_tb = tb; 233 cpumask_andnot(&wd_smp_cpus_pending, 234 &wd_cpus_enabled, 235 &wd_smp_cpus_stuck); 236 } 237 wd_smp_unlock(&flags); 238 } 239 } 240 241 static void watchdog_timer_interrupt(int cpu) 242 { 243 u64 tb = get_tb(); 244 245 per_cpu(wd_timer_tb, cpu) = tb; 246 247 wd_smp_clear_cpu_pending(cpu, tb); 248 249 if ((s64)(tb - wd_smp_last_reset_tb) >= (s64)wd_smp_panic_timeout_tb) 250 watchdog_smp_panic(cpu, tb); 251 } 252 253 DEFINE_INTERRUPT_HANDLER_NMI(soft_nmi_interrupt) 254 { 255 unsigned long flags; 256 int cpu = raw_smp_processor_id(); 257 u64 tb; 258 259 /* should only arrive from kernel, with irqs disabled */ 260 WARN_ON_ONCE(!arch_irq_disabled_regs(regs)); 261 262 if (!cpumask_test_cpu(cpu, &wd_cpus_enabled)) 263 return 0; 264 265 __this_cpu_inc(irq_stat.soft_nmi_irqs); 266 267 tb = get_tb(); 268 if (tb - per_cpu(wd_timer_tb, cpu) >= wd_panic_timeout_tb) { 269 wd_smp_lock(&flags); 270 if (cpumask_test_cpu(cpu, &wd_smp_cpus_stuck)) { 271 wd_smp_unlock(&flags); 272 return 0; 273 } 274 set_cpu_stuck(cpu, tb); 275 276 pr_emerg("CPU %d self-detected hard LOCKUP @ %pS\n", 277 cpu, (void *)regs->nip); 278 pr_emerg("CPU %d TB:%lld, last heartbeat TB:%lld (%lldms ago)\n", 279 cpu, tb, per_cpu(wd_timer_tb, cpu), 280 tb_to_ns(tb - per_cpu(wd_timer_tb, cpu)) / 1000000); 281 print_modules(); 282 print_irqtrace_events(current); 283 show_regs(regs); 284 285 wd_smp_unlock(&flags); 286 287 if (sysctl_hardlockup_all_cpu_backtrace) 288 trigger_allbutself_cpu_backtrace(); 289 290 if (hardlockup_panic) 291 nmi_panic(regs, "Hard LOCKUP"); 292 } 293 if (wd_panic_timeout_tb < 0x7fffffff) 294 mtspr(SPRN_DEC, wd_panic_timeout_tb); 295 296 return 0; 297 } 298 299 static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) 300 { 301 int cpu = smp_processor_id(); 302 303 if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED)) 304 return HRTIMER_NORESTART; 305 306 if (!cpumask_test_cpu(cpu, &watchdog_cpumask)) 307 return HRTIMER_NORESTART; 308 309 watchdog_timer_interrupt(cpu); 310 311 hrtimer_forward_now(hrtimer, ms_to_ktime(wd_timer_period_ms)); 312 313 return HRTIMER_RESTART; 314 } 315 316 void arch_touch_nmi_watchdog(void) 317 { 318 unsigned long ticks = tb_ticks_per_usec * wd_timer_period_ms * 1000; 319 int cpu = smp_processor_id(); 320 u64 tb = get_tb(); 321 322 if (tb - per_cpu(wd_timer_tb, cpu) >= ticks) { 323 per_cpu(wd_timer_tb, cpu) = tb; 324 wd_smp_clear_cpu_pending(cpu, tb); 325 } 326 } 327 EXPORT_SYMBOL(arch_touch_nmi_watchdog); 328 329 static void start_watchdog(void *arg) 330 { 331 struct hrtimer *hrtimer = this_cpu_ptr(&wd_hrtimer); 332 int cpu = smp_processor_id(); 333 unsigned long flags; 334 335 if (cpumask_test_cpu(cpu, &wd_cpus_enabled)) { 336 WARN_ON(1); 337 return; 338 } 339 340 if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED)) 341 return; 342 343 if (!cpumask_test_cpu(cpu, &watchdog_cpumask)) 344 return; 345 346 wd_smp_lock(&flags); 347 cpumask_set_cpu(cpu, &wd_cpus_enabled); 348 if (cpumask_weight(&wd_cpus_enabled) == 1) { 349 cpumask_set_cpu(cpu, &wd_smp_cpus_pending); 350 wd_smp_last_reset_tb = get_tb(); 351 } 352 wd_smp_unlock(&flags); 353 354 *this_cpu_ptr(&wd_timer_tb) = get_tb(); 355 356 hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); 357 hrtimer->function = watchdog_timer_fn; 358 hrtimer_start(hrtimer, ms_to_ktime(wd_timer_period_ms), 359 HRTIMER_MODE_REL_PINNED); 360 } 361 362 static int start_watchdog_on_cpu(unsigned int cpu) 363 { 364 return smp_call_function_single(cpu, start_watchdog, NULL, true); 365 } 366 367 static void stop_watchdog(void *arg) 368 { 369 struct hrtimer *hrtimer = this_cpu_ptr(&wd_hrtimer); 370 int cpu = smp_processor_id(); 371 unsigned long flags; 372 373 if (!cpumask_test_cpu(cpu, &wd_cpus_enabled)) 374 return; /* Can happen in CPU unplug case */ 375 376 hrtimer_cancel(hrtimer); 377 378 wd_smp_lock(&flags); 379 cpumask_clear_cpu(cpu, &wd_cpus_enabled); 380 wd_smp_unlock(&flags); 381 382 wd_smp_clear_cpu_pending(cpu, get_tb()); 383 } 384 385 static int stop_watchdog_on_cpu(unsigned int cpu) 386 { 387 return smp_call_function_single(cpu, stop_watchdog, NULL, true); 388 } 389 390 static void watchdog_calc_timeouts(void) 391 { 392 wd_panic_timeout_tb = watchdog_thresh * ppc_tb_freq; 393 394 /* Have the SMP detector trigger a bit later */ 395 wd_smp_panic_timeout_tb = wd_panic_timeout_tb * 3 / 2; 396 397 /* 2/5 is the factor that the perf based detector uses */ 398 wd_timer_period_ms = watchdog_thresh * 1000 * 2 / 5; 399 } 400 401 void watchdog_nmi_stop(void) 402 { 403 int cpu; 404 405 for_each_cpu(cpu, &wd_cpus_enabled) 406 stop_watchdog_on_cpu(cpu); 407 } 408 409 void watchdog_nmi_start(void) 410 { 411 int cpu; 412 413 watchdog_calc_timeouts(); 414 for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask) 415 start_watchdog_on_cpu(cpu); 416 } 417 418 /* 419 * Invoked from core watchdog init. 420 */ 421 int __init watchdog_nmi_probe(void) 422 { 423 int err; 424 425 err = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, 426 "powerpc/watchdog:online", 427 start_watchdog_on_cpu, 428 stop_watchdog_on_cpu); 429 if (err < 0) { 430 pr_warn("could not be initialized"); 431 return err; 432 } 433 return 0; 434 } 435