1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * Detect Hung Task 4 * 5 * kernel/hung_task.c - kernel thread for detecting tasks stuck in D state 6 * 7 */ 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/export.h> 18 #include <linux/panic_notifier.h> 19 #include <linux/sysctl.h> 20 #include <linux/suspend.h> 21 #include <linux/utsname.h> 22 #include <linux/sched/signal.h> 23 #include <linux/sched/debug.h> 24 #include <linux/sched/sysctl.h> 25 26 #include <trace/events/sched.h> 27 28 /* 29 * The number of tasks checked: 30 */ 31 static int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT; 32 33 /* 34 * Total number of tasks detected as hung since boot: 35 */ 36 static unsigned long __read_mostly sysctl_hung_task_detect_count; 37 38 /* 39 * Limit number of tasks checked in a batch. 40 * 41 * This value controls the preemptibility of khungtaskd since preemption 42 * is disabled during the critical section. It also controls the size of 43 * the RCU grace period. So it needs to be upper-bound. 44 */ 45 #define HUNG_TASK_LOCK_BREAK (HZ / 10) 46 47 /* 48 * Zero means infinite timeout - no checking done: 49 */ 50 unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT; 51 EXPORT_SYMBOL_GPL(sysctl_hung_task_timeout_secs); 52 53 /* 54 * Zero (default value) means use sysctl_hung_task_timeout_secs: 55 */ 56 static unsigned long __read_mostly sysctl_hung_task_check_interval_secs; 57 58 static int __read_mostly sysctl_hung_task_warnings = 10; 59 60 static int __read_mostly did_panic; 61 static bool hung_task_show_lock; 62 static bool hung_task_call_panic; 63 static bool hung_task_show_all_bt; 64 65 static struct task_struct *watchdog_task; 66 67 #ifdef CONFIG_SMP 68 /* 69 * Should we dump all CPUs backtraces in a hung task event? 70 * Defaults to 0, can be changed via sysctl. 71 */ 72 static unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace; 73 #else 74 #define sysctl_hung_task_all_cpu_backtrace 0 75 #endif /* CONFIG_SMP */ 76 77 /* 78 * Should we panic (and reboot, if panic_timeout= is set) when a 79 * hung task is detected: 80 */ 81 static unsigned int __read_mostly sysctl_hung_task_panic = 82 IS_ENABLED(CONFIG_BOOTPARAM_HUNG_TASK_PANIC); 83 84 static int 85 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr) 86 { 87 did_panic = 1; 88 89 return NOTIFY_DONE; 90 } 91 92 static struct notifier_block panic_block = { 93 .notifier_call = hung_task_panic, 94 }; 95 96 static void check_hung_task(struct task_struct *t, unsigned long timeout) 97 { 98 unsigned long switch_count = t->nvcsw + t->nivcsw; 99 100 /* 101 * Ensure the task is not frozen. 102 * Also, skip vfork and any other user process that freezer should skip. 103 */ 104 if (unlikely(READ_ONCE(t->__state) & TASK_FROZEN)) 105 return; 106 107 /* 108 * When a freshly created task is scheduled once, changes its state to 109 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it 110 * musn't be checked. 111 */ 112 if (unlikely(!switch_count)) 113 return; 114 115 if (switch_count != t->last_switch_count) { 116 t->last_switch_count = switch_count; 117 t->last_switch_time = jiffies; 118 return; 119 } 120 if (time_is_after_jiffies(t->last_switch_time + timeout * HZ)) 121 return; 122 123 /* 124 * This counter tracks the total number of tasks detected as hung 125 * since boot. 126 */ 127 sysctl_hung_task_detect_count++; 128 129 trace_sched_process_hang(t); 130 131 if (sysctl_hung_task_panic) { 132 console_verbose(); 133 hung_task_show_lock = true; 134 hung_task_call_panic = true; 135 } 136 137 /* 138 * Ok, the task did not get scheduled for more than 2 minutes, 139 * complain: 140 */ 141 if (sysctl_hung_task_warnings || hung_task_call_panic) { 142 if (sysctl_hung_task_warnings > 0) 143 sysctl_hung_task_warnings--; 144 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n", 145 t->comm, t->pid, (jiffies - t->last_switch_time) / HZ); 146 pr_err(" %s %s %.*s\n", 147 print_tainted(), init_utsname()->release, 148 (int)strcspn(init_utsname()->version, " "), 149 init_utsname()->version); 150 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\"" 151 " disables this message.\n"); 152 sched_show_task(t); 153 hung_task_show_lock = true; 154 155 if (sysctl_hung_task_all_cpu_backtrace) 156 hung_task_show_all_bt = true; 157 if (!sysctl_hung_task_warnings) 158 pr_info("Future hung task reports are suppressed, see sysctl kernel.hung_task_warnings\n"); 159 } 160 161 touch_nmi_watchdog(); 162 } 163 164 /* 165 * To avoid extending the RCU grace period for an unbounded amount of time, 166 * periodically exit the critical section and enter a new one. 167 * 168 * For preemptible RCU it is sufficient to call rcu_read_unlock in order 169 * to exit the grace period. For classic RCU, a reschedule is required. 170 */ 171 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t) 172 { 173 bool can_cont; 174 175 get_task_struct(g); 176 get_task_struct(t); 177 rcu_read_unlock(); 178 cond_resched(); 179 rcu_read_lock(); 180 can_cont = pid_alive(g) && pid_alive(t); 181 put_task_struct(t); 182 put_task_struct(g); 183 184 return can_cont; 185 } 186 187 /* 188 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for 189 * a really long time (120 seconds). If that happens, print out 190 * a warning. 191 */ 192 static void check_hung_uninterruptible_tasks(unsigned long timeout) 193 { 194 int max_count = sysctl_hung_task_check_count; 195 unsigned long last_break = jiffies; 196 struct task_struct *g, *t; 197 198 /* 199 * If the system crashed already then all bets are off, 200 * do not report extra hung tasks: 201 */ 202 if (test_taint(TAINT_DIE) || did_panic) 203 return; 204 205 hung_task_show_lock = false; 206 rcu_read_lock(); 207 for_each_process_thread(g, t) { 208 unsigned int state; 209 210 if (!max_count--) 211 goto unlock; 212 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) { 213 if (!rcu_lock_break(g, t)) 214 goto unlock; 215 last_break = jiffies; 216 } 217 /* 218 * skip the TASK_KILLABLE tasks -- these can be killed 219 * skip the TASK_IDLE tasks -- those are genuinely idle 220 */ 221 state = READ_ONCE(t->__state); 222 if ((state & TASK_UNINTERRUPTIBLE) && 223 !(state & TASK_WAKEKILL) && 224 !(state & TASK_NOLOAD)) 225 check_hung_task(t, timeout); 226 } 227 unlock: 228 rcu_read_unlock(); 229 if (hung_task_show_lock) 230 debug_show_all_locks(); 231 232 if (hung_task_show_all_bt) { 233 hung_task_show_all_bt = false; 234 trigger_all_cpu_backtrace(); 235 } 236 237 if (hung_task_call_panic) 238 panic("hung_task: blocked tasks"); 239 } 240 241 static long hung_timeout_jiffies(unsigned long last_checked, 242 unsigned long timeout) 243 { 244 /* timeout of 0 will disable the watchdog */ 245 return timeout ? last_checked - jiffies + timeout * HZ : 246 MAX_SCHEDULE_TIMEOUT; 247 } 248 249 #ifdef CONFIG_SYSCTL 250 /* 251 * Process updating of timeout sysctl 252 */ 253 static int proc_dohung_task_timeout_secs(const struct ctl_table *table, int write, 254 void *buffer, 255 size_t *lenp, loff_t *ppos) 256 { 257 int ret; 258 259 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); 260 261 if (ret || !write) 262 goto out; 263 264 wake_up_process(watchdog_task); 265 266 out: 267 return ret; 268 } 269 270 /* 271 * This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs 272 * and hung_task_check_interval_secs 273 */ 274 static const unsigned long hung_task_timeout_max = (LONG_MAX / HZ); 275 static struct ctl_table hung_task_sysctls[] = { 276 #ifdef CONFIG_SMP 277 { 278 .procname = "hung_task_all_cpu_backtrace", 279 .data = &sysctl_hung_task_all_cpu_backtrace, 280 .maxlen = sizeof(int), 281 .mode = 0644, 282 .proc_handler = proc_dointvec_minmax, 283 .extra1 = SYSCTL_ZERO, 284 .extra2 = SYSCTL_ONE, 285 }, 286 #endif /* CONFIG_SMP */ 287 { 288 .procname = "hung_task_panic", 289 .data = &sysctl_hung_task_panic, 290 .maxlen = sizeof(int), 291 .mode = 0644, 292 .proc_handler = proc_dointvec_minmax, 293 .extra1 = SYSCTL_ZERO, 294 .extra2 = SYSCTL_ONE, 295 }, 296 { 297 .procname = "hung_task_check_count", 298 .data = &sysctl_hung_task_check_count, 299 .maxlen = sizeof(int), 300 .mode = 0644, 301 .proc_handler = proc_dointvec_minmax, 302 .extra1 = SYSCTL_ZERO, 303 }, 304 { 305 .procname = "hung_task_timeout_secs", 306 .data = &sysctl_hung_task_timeout_secs, 307 .maxlen = sizeof(unsigned long), 308 .mode = 0644, 309 .proc_handler = proc_dohung_task_timeout_secs, 310 .extra2 = (void *)&hung_task_timeout_max, 311 }, 312 { 313 .procname = "hung_task_check_interval_secs", 314 .data = &sysctl_hung_task_check_interval_secs, 315 .maxlen = sizeof(unsigned long), 316 .mode = 0644, 317 .proc_handler = proc_dohung_task_timeout_secs, 318 .extra2 = (void *)&hung_task_timeout_max, 319 }, 320 { 321 .procname = "hung_task_warnings", 322 .data = &sysctl_hung_task_warnings, 323 .maxlen = sizeof(int), 324 .mode = 0644, 325 .proc_handler = proc_dointvec_minmax, 326 .extra1 = SYSCTL_NEG_ONE, 327 }, 328 { 329 .procname = "hung_task_detect_count", 330 .data = &sysctl_hung_task_detect_count, 331 .maxlen = sizeof(unsigned long), 332 .mode = 0444, 333 .proc_handler = proc_doulongvec_minmax, 334 }, 335 }; 336 337 static void __init hung_task_sysctl_init(void) 338 { 339 register_sysctl_init("kernel", hung_task_sysctls); 340 } 341 #else 342 #define hung_task_sysctl_init() do { } while (0) 343 #endif /* CONFIG_SYSCTL */ 344 345 346 static atomic_t reset_hung_task = ATOMIC_INIT(0); 347 348 void reset_hung_task_detector(void) 349 { 350 atomic_set(&reset_hung_task, 1); 351 } 352 EXPORT_SYMBOL_GPL(reset_hung_task_detector); 353 354 static bool hung_detector_suspended; 355 356 static int hungtask_pm_notify(struct notifier_block *self, 357 unsigned long action, void *hcpu) 358 { 359 switch (action) { 360 case PM_SUSPEND_PREPARE: 361 case PM_HIBERNATION_PREPARE: 362 case PM_RESTORE_PREPARE: 363 hung_detector_suspended = true; 364 break; 365 case PM_POST_SUSPEND: 366 case PM_POST_HIBERNATION: 367 case PM_POST_RESTORE: 368 hung_detector_suspended = false; 369 break; 370 default: 371 break; 372 } 373 return NOTIFY_OK; 374 } 375 376 /* 377 * kthread which checks for tasks stuck in D state 378 */ 379 static int watchdog(void *dummy) 380 { 381 unsigned long hung_last_checked = jiffies; 382 383 set_user_nice(current, 0); 384 385 for ( ; ; ) { 386 unsigned long timeout = sysctl_hung_task_timeout_secs; 387 unsigned long interval = sysctl_hung_task_check_interval_secs; 388 long t; 389 390 if (interval == 0) 391 interval = timeout; 392 interval = min_t(unsigned long, interval, timeout); 393 t = hung_timeout_jiffies(hung_last_checked, interval); 394 if (t <= 0) { 395 if (!atomic_xchg(&reset_hung_task, 0) && 396 !hung_detector_suspended) 397 check_hung_uninterruptible_tasks(timeout); 398 hung_last_checked = jiffies; 399 continue; 400 } 401 schedule_timeout_interruptible(t); 402 } 403 404 return 0; 405 } 406 407 static int __init hung_task_init(void) 408 { 409 atomic_notifier_chain_register(&panic_notifier_list, &panic_block); 410 411 /* Disable hung task detector on suspend */ 412 pm_notifier(hungtask_pm_notify, 0); 413 414 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd"); 415 hung_task_sysctl_init(); 416 417 return 0; 418 } 419 subsys_initcall(hung_task_init); 420