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/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 }