arch/powerpc/kernel/watchdog.c

   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 }