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