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         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 }