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