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