kernel/softlockup.c

   1 /*
   2  * Detect Soft Lockups
   3  *
   4  * started by Ingo Molnar, Copyright (C) 2005, 2006 Red Hat, Inc.
   5  *
   6  * this code detects soft lockups: incidents in where on a CPU
   7  * the kernel does not reschedule for 10 seconds or more.
   8  */
   9 #include <linux/mm.h>
  10 #include <linux/cpu.h>
  11 #include <linux/nmi.h>
  12 #include <linux/init.h>
  13 #include <linux/delay.h>
  14 #include <linux/freezer.h>
  15 #include <linux/kthread.h>
  16 #include <linux/lockdep.h>
  17 #include <linux/notifier.h>
  18 #include <linux/module.h>
  19 #include <linux/sysctl.h>
  20
  21 #include <asm/irq_regs.h>
  22
  23 static DEFINE_SPINLOCK(print_lock);
  24
  25 static DEFINE_PER_CPU(unsigned long, touch_timestamp);
  26 static DEFINE_PER_CPU(unsigned long, print_timestamp);
  27 static DEFINE_PER_CPU(struct task_struct *, watchdog_task);
  28
  29 static int __read_mostly did_panic;
  30 int __read_mostly softlockup_thresh = 60;
  31
  32 /*
  33  * Should we panic (and reboot, if panic_timeout= is set) when a
  34  * soft-lockup occurs:
  35  */
  36 unsigned int __read_mostly softlockup_panic =
  37                                 CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
  38
  39 static int __init softlockup_panic_setup(char *str)
  40 {
  41         softlockup_panic = simple_strtoul(str, NULL, 0);
  42
  43         return 1;
  44 }
  45 __setup("softlockup_panic=", softlockup_panic_setup);
  46
  47 static int
  48 softlock_panic(struct notifier_block *this, unsigned long event, void *ptr)
  49 {
  50         did_panic = 1;
  51
  52         return NOTIFY_DONE;
  53 }
  54
  55 static struct notifier_block panic_block = {
  56         .notifier_call = softlock_panic,
  57 };
  58
  59 /*
  60  * Returns seconds, approximately.  We don't need nanosecond
  61  * resolution, and we don't need to waste time with a big divide when
  62  * 2^30ns == 1.074s.
  63  */
  64 static unsigned long get_timestamp(int this_cpu)
  65 {
  66         return cpu_clock(this_cpu) >> 30LL;  /* 2^30 ~= 10^9 */
  67 }
  68
  69 static void __touch_softlockup_watchdog(void)
  70 {
  71         int this_cpu = raw_smp_processor_id();
  72
  73         __raw_get_cpu_var(touch_timestamp) = get_timestamp(this_cpu);
  74 }
  75
  76 void touch_softlockup_watchdog(void)
  77 {
  78         __raw_get_cpu_var(touch_timestamp) = 0;
  79 }
  80 EXPORT_SYMBOL(touch_softlockup_watchdog);
  81
  82 void touch_all_softlockup_watchdogs(void)
  83 {
  84         int cpu;
  85
  86         /* Cause each CPU to re-update its timestamp rather than complain */
  87         for_each_online_cpu(cpu)
  88                 per_cpu(touch_timestamp, cpu) = 0;
  89 }
  90 EXPORT_SYMBOL(touch_all_softlockup_watchdogs);
  91
  92 int proc_dosoftlockup_thresh(struct ctl_table *table, int write,
  93                              struct file *filp, void __user *buffer,
  94                              size_t *lenp, loff_t *ppos)
  95 {
  96         touch_all_softlockup_watchdogs();
  97         return proc_dointvec_minmax(table, write, filp, buffer, lenp, ppos);
  98 }
  99
 100 /*
 101  * This callback runs from the timer interrupt, and checks
 102  * whether the watchdog thread has hung or not:
 103  */
 104 void softlockup_tick(void)
 105 {
 106         int this_cpu = smp_processor_id();
 107         unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu);
 108         unsigned long print_timestamp;
 109         struct pt_regs *regs = get_irq_regs();
 110         unsigned long now;
 111
 112         /* Is detection switched off? */
 113         if (!per_cpu(watchdog_task, this_cpu) || softlockup_thresh <= 0) {
 114                 /* Be sure we don't false trigger if switched back on */
 115                 if (touch_timestamp)
 116                         per_cpu(touch_timestamp, this_cpu) = 0;
 117                 return;
 118         }
 119
 120         if (touch_timestamp == 0) {
 121                 __touch_softlockup_watchdog();
 122                 return;
 123         }
 124
 125         print_timestamp = per_cpu(print_timestamp, this_cpu);
 126
 127         /* report at most once a second */
 128         if (print_timestamp == touch_timestamp || did_panic)
 129                 return;
 130
 131         /* do not print during early bootup: */
 132         if (unlikely(system_state != SYSTEM_RUNNING)) {
 133                 __touch_softlockup_watchdog();
 134                 return;
 135         }
 136
 137         now = get_timestamp(this_cpu);
 138
 139         /*
 140          * Wake up the high-prio watchdog task twice per
 141          * threshold timespan.
 142          */
 143         if (now > touch_timestamp + softlockup_thresh/2)
 144                 wake_up_process(per_cpu(watchdog_task, this_cpu));
 145
 146         /* Warn about unreasonable delays: */
 147         if (now <= (touch_timestamp + softlockup_thresh))
 148                 return;
 149
 150         per_cpu(print_timestamp, this_cpu) = touch_timestamp;
 151
 152         spin_lock(&print_lock);
 153         printk(KERN_ERR "BUG: soft lockup - CPU#%d stuck for %lus! [%s:%d]\n",
 154                         this_cpu, now - touch_timestamp,
 155                         current->comm, task_pid_nr(current));
 156         print_modules();
 157         print_irqtrace_events(current);
 158         if (regs)
 159                 show_regs(regs);
 160         else
 161                 dump_stack();
 162         spin_unlock(&print_lock);
 163
 164         if (softlockup_panic)
 165                 panic("softlockup: hung tasks");
 166 }
 167
 168 /*
 169  * Have a reasonable limit on the number of tasks checked:
 170  */
 171 unsigned long __read_mostly sysctl_hung_task_check_count = 1024;
 172
 173 /*
 174  * Zero means infinite timeout - no checking done:
 175  */
 176 unsigned long __read_mostly sysctl_hung_task_timeout_secs = 480;
 177
 178 unsigned long __read_mostly sysctl_hung_task_warnings = 10;
 179
 180 /*
 181  * Only do the hung-tasks check on one CPU:
 182  */
 183 static int check_cpu __read_mostly = -1;
 184
 185 static void check_hung_task(struct task_struct *t, unsigned long now)
 186 {
 187         unsigned long switch_count = t->nvcsw + t->nivcsw;
 188
 189         if (t->flags & PF_FROZEN)
 190                 return;
 191
 192         if (switch_count != t->last_switch_count || !t->last_switch_timestamp) {
 193                 t->last_switch_count = switch_count;
 194                 t->last_switch_timestamp = now;
 195                 return;
 196         }
 197         if ((long)(now - t->last_switch_timestamp) <
 198                                         sysctl_hung_task_timeout_secs)
 199                 return;
 200         if (!sysctl_hung_task_warnings)
 201                 return;
 202         sysctl_hung_task_warnings--;
 203
 204         /*
 205          * Ok, the task did not get scheduled for more than 2 minutes,
 206          * complain:
 207          */
 208         printk(KERN_ERR "INFO: task %s:%d blocked for more than "
 209                         "%ld seconds.\n", t->comm, t->pid,
 210                         sysctl_hung_task_timeout_secs);
 211         printk(KERN_ERR "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
 212                         " disables this message.\n");
 213         sched_show_task(t);
 214         __debug_show_held_locks(t);
 215
 216         t->last_switch_timestamp = now;
 217         touch_nmi_watchdog();
 218
 219         if (softlockup_panic)
 220                 panic("softlockup: blocked tasks");
 221 }
 222
 223 /*
 224  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 225  * a really long time (120 seconds). If that happens, print out
 226  * a warning.
 227  */
 228 static void check_hung_uninterruptible_tasks(int this_cpu)
 229 {
 230         int max_count = sysctl_hung_task_check_count;
 231         unsigned long now = get_timestamp(this_cpu);
 232         struct task_struct *g, *t;
 233
 234         /*
 235          * If the system crashed already then all bets are off,
 236          * do not report extra hung tasks:
 237          */
 238         if (test_taint(TAINT_DIE) || did_panic)
 239                 return;
 240
 241         read_lock(&tasklist_lock);
 242         do_each_thread(g, t) {
 243                 if (!--max_count)
 244                         goto unlock;
 245                 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
 246                 if (t->state == TASK_UNINTERRUPTIBLE)
 247                         check_hung_task(t, now);
 248         } while_each_thread(g, t);
 249  unlock:
 250         read_unlock(&tasklist_lock);
 251 }
 252
 253 /*
 254  * The watchdog thread - runs every second and touches the timestamp.
 255  */
 256 static int watchdog(void *__bind_cpu)
 257 {
 258         struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
 259         int this_cpu = (long)__bind_cpu;
 260
 261         sched_setscheduler(current, SCHED_FIFO, &param);
 262
 263         /* initialize timestamp */
 264         __touch_softlockup_watchdog();
 265
 266         set_current_state(TASK_INTERRUPTIBLE);
 267         /*
 268          * Run briefly once per second to reset the softlockup timestamp.
 269          * If this gets delayed for more than 60 seconds then the
 270          * debug-printout triggers in softlockup_tick().
 271          */
 272         while (!kthread_should_stop()) {
 273                 __touch_softlockup_watchdog();
 274                 schedule();
 275
 276                 if (kthread_should_stop())
 277                         break;
 278
 279                 if (this_cpu == check_cpu) {
 280                         if (sysctl_hung_task_timeout_secs)
 281                                 check_hung_uninterruptible_tasks(this_cpu);
 282                 }
 283
 284                 set_current_state(TASK_INTERRUPTIBLE);
 285         }
 286         __set_current_state(TASK_RUNNING);
 287
 288         return 0;
 289 }
 290
 291 /*
 292  * Create/destroy watchdog threads as CPUs come and go:
 293  */
 294 static int __cpuinit
 295 cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
 296 {
 297         int hotcpu = (unsigned long)hcpu;
 298         struct task_struct *p;
 299
 300         switch (action) {
 301         case CPU_UP_PREPARE:
 302         case CPU_UP_PREPARE_FROZEN:
 303                 BUG_ON(per_cpu(watchdog_task, hotcpu));
 304                 p = kthread_create(watchdog, hcpu, "watchdog/%d", hotcpu);
 305                 if (IS_ERR(p)) {
 306                         printk(KERN_ERR "watchdog for %i failed\n", hotcpu);
 307                         return NOTIFY_BAD;
 308                 }
 309                 per_cpu(touch_timestamp, hotcpu) = 0;
 310                 per_cpu(watchdog_task, hotcpu) = p;
 311                 kthread_bind(p, hotcpu);
 312                 break;
 313         case CPU_ONLINE:
 314         case CPU_ONLINE_FROZEN:
 315                 check_cpu = cpumask_any(cpu_online_mask);
 316                 wake_up_process(per_cpu(watchdog_task, hotcpu));
 317                 break;
 318 #ifdef CONFIG_HOTPLUG_CPU
 319         case CPU_DOWN_PREPARE:
 320         case CPU_DOWN_PREPARE_FROZEN:
 321                 if (hotcpu == check_cpu) {
 322                         /* Pick any other online cpu. */
 323                         check_cpu = cpumask_any_but(cpu_online_mask, hotcpu);
 324                 }
 325                 break;
 326
 327         case CPU_UP_CANCELED:
 328         case CPU_UP_CANCELED_FROZEN:
 329                 if (!per_cpu(watchdog_task, hotcpu))
 330                         break;
 331                 /* Unbind so it can run.  Fall thru. */
 332                 kthread_bind(per_cpu(watchdog_task, hotcpu),
 333                              cpumask_any(cpu_online_mask));
 334         case CPU_DEAD:
 335         case CPU_DEAD_FROZEN:
 336                 p = per_cpu(watchdog_task, hotcpu);
 337                 per_cpu(watchdog_task, hotcpu) = NULL;
 338                 kthread_stop(p);
 339                 break;
 340 #endif /* CONFIG_HOTPLUG_CPU */
 341         }
 342         return NOTIFY_OK;
 343 }
 344
 345 static struct notifier_block __cpuinitdata cpu_nfb = {
 346         .notifier_call = cpu_callback
 347 };
 348
 349 static int __initdata nosoftlockup;
 350
 351 static int __init nosoftlockup_setup(char *str)
 352 {
 353         nosoftlockup = 1;
 354         return 1;
 355 }
 356 __setup("nosoftlockup", nosoftlockup_setup);
 357
 358 static int __init spawn_softlockup_task(void)
 359 {
 360         void *cpu = (void *)(long)smp_processor_id();
 361         int err;
 362
 363         if (nosoftlockup)
 364                 return 0;
 365
 366         err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
 367         if (err == NOTIFY_BAD) {
 368                 BUG();
 369                 return 1;
 370         }
 371         cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
 372         register_cpu_notifier(&cpu_nfb);
 373
 374         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 375
 376         return 0;
 377 }
 378 early_initcall(spawn_softlockup_task);