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 if (t->flags & PF_POSTCOREDUMP) 151 pr_err(" Blocked by coredump.\n"); 152 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\"" 153 " disables this message.\n"); 154 sched_show_task(t); 155 hung_task_show_lock = true; 156 157 if (sysctl_hung_task_all_cpu_backtrace) 158 hung_task_show_all_bt = true; 159 if (!sysctl_hung_task_warnings) 160 pr_info("Future hung task reports are suppressed, see sysctl kernel.hung_task_warnings\n"); 161 } 162 163 touch_nmi_watchdog(); 164 } 165 166 /* 167 * To avoid extending the RCU grace period for an unbounded amount of time, 168 * periodically exit the critical section and enter a new one. 169 * 170 * For preemptible RCU it is sufficient to call rcu_read_unlock in order 171 * to exit the grace period. For classic RCU, a reschedule is required. 172 */ 173 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t) 174 { 175 bool can_cont; 176 177 get_task_struct(g); 178 get_task_struct(t); 179 rcu_read_unlock(); 180 cond_resched(); 181 rcu_read_lock(); 182 can_cont = pid_alive(g) && pid_alive(t); 183 put_task_struct(t); 184 put_task_struct(g); 185 186 return can_cont; 187 } 188 189 /* 190 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for 191 * a really long time (120 seconds). If that happens, print out 192 * a warning. 193 */ 194 static void check_hung_uninterruptible_tasks(unsigned long timeout) 195 { 196 int max_count = sysctl_hung_task_check_count; 197 unsigned long last_break = jiffies; 198 struct task_struct *g, *t; 199 200 /* 201 * If the system crashed already then all bets are off, 202 * do not report extra hung tasks: 203 */ 204 if (test_taint(TAINT_DIE) || did_panic) 205 return; 206 207 hung_task_show_lock = false; 208 rcu_read_lock(); 209 for_each_process_thread(g, t) { 210 unsigned int state; 211 212 if (!max_count--) 213 goto unlock; 214 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) { 215 if (!rcu_lock_break(g, t)) 216 goto unlock; 217 last_break = jiffies; 218 } 219 /* 220 * skip the TASK_KILLABLE tasks -- these can be killed 221 * skip the TASK_IDLE tasks -- those are genuinely idle 222 */ 223 state = READ_ONCE(t->__state); 224 if ((state & TASK_UNINTERRUPTIBLE) && 225 !(state & TASK_WAKEKILL) && 226 !(state & TASK_NOLOAD)) 227 check_hung_task(t, timeout); 228 } 229 unlock: 230 rcu_read_unlock(); 231 if (hung_task_show_lock) 232 debug_show_all_locks(); 233 234 if (hung_task_show_all_bt) { 235 hung_task_show_all_bt = false; 236 trigger_all_cpu_backtrace(); 237 } 238 239 if (hung_task_call_panic) 240 panic("hung_task: blocked tasks"); 241 } 242 243 static long hung_timeout_jiffies(unsigned long last_checked, 244 unsigned long timeout) 245 { 246 /* timeout of 0 will disable the watchdog */ 247 return timeout ? last_checked - jiffies + timeout * HZ : 248 MAX_SCHEDULE_TIMEOUT; 249 } 250 251 #ifdef CONFIG_SYSCTL 252 /* 253 * Process updating of timeout sysctl 254 */ 255 static int proc_dohung_task_timeout_secs(const struct ctl_table *table, int write, 256 void *buffer, 257 size_t *lenp, loff_t *ppos) 258 { 259 int ret; 260 261 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); 262 263 if (ret || !write) 264 goto out; 265 266 wake_up_process(watchdog_task); 267 268 out: 269 return ret; 270 } 271 272 /* 273 * This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs 274 * and hung_task_check_interval_secs 275 */ 276 static const unsigned long hung_task_timeout_max = (LONG_MAX / HZ); 277 static const struct ctl_table hung_task_sysctls[] = { 278 #ifdef CONFIG_SMP 279 { 280 .procname = "hung_task_all_cpu_backtrace", 281 .data = &sysctl_hung_task_all_cpu_backtrace, 282 .maxlen = sizeof(int), 283 .mode = 0644, 284 .proc_handler = proc_dointvec_minmax, 285 .extra1 = SYSCTL_ZERO, 286 .extra2 = SYSCTL_ONE, 287 }, 288 #endif /* CONFIG_SMP */ 289 { 290 .procname = "hung_task_panic", 291 .data = &sysctl_hung_task_panic, 292 .maxlen = sizeof(int), 293 .mode = 0644, 294 .proc_handler = proc_dointvec_minmax, 295 .extra1 = SYSCTL_ZERO, 296 .extra2 = SYSCTL_ONE, 297 }, 298 { 299 .procname = "hung_task_check_count", 300 .data = &sysctl_hung_task_check_count, 301 .maxlen = sizeof(int), 302 .mode = 0644, 303 .proc_handler = proc_dointvec_minmax, 304 .extra1 = SYSCTL_ZERO, 305 }, 306 { 307 .procname = "hung_task_timeout_secs", 308 .data = &sysctl_hung_task_timeout_secs, 309 .maxlen = sizeof(unsigned long), 310 .mode = 0644, 311 .proc_handler = proc_dohung_task_timeout_secs, 312 .extra2 = (void *)&hung_task_timeout_max, 313 }, 314 { 315 .procname = "hung_task_check_interval_secs", 316 .data = &sysctl_hung_task_check_interval_secs, 317 .maxlen = sizeof(unsigned long), 318 .mode = 0644, 319 .proc_handler = proc_dohung_task_timeout_secs, 320 .extra2 = (void *)&hung_task_timeout_max, 321 }, 322 { 323 .procname = "hung_task_warnings", 324 .data = &sysctl_hung_task_warnings, 325 .maxlen = sizeof(int), 326 .mode = 0644, 327 .proc_handler = proc_dointvec_minmax, 328 .extra1 = SYSCTL_NEG_ONE, 329 }, 330 { 331 .procname = "hung_task_detect_count", 332 .data = &sysctl_hung_task_detect_count, 333 .maxlen = sizeof(unsigned long), 334 .mode = 0444, 335 .proc_handler = proc_doulongvec_minmax, 336 }, 337 }; 338 339 static void __init hung_task_sysctl_init(void) 340 { 341 register_sysctl_init("kernel", hung_task_sysctls); 342 } 343 #else 344 #define hung_task_sysctl_init() do { } while (0) 345 #endif /* CONFIG_SYSCTL */ 346 347 348 static atomic_t reset_hung_task = ATOMIC_INIT(0); 349 350 void reset_hung_task_detector(void) 351 { 352 atomic_set(&reset_hung_task, 1); 353 } 354 EXPORT_SYMBOL_GPL(reset_hung_task_detector); 355 356 static bool hung_detector_suspended; 357 358 static int hungtask_pm_notify(struct notifier_block *self, 359 unsigned long action, void *hcpu) 360 { 361 switch (action) { 362 case PM_SUSPEND_PREPARE: 363 case PM_HIBERNATION_PREPARE: 364 case PM_RESTORE_PREPARE: 365 hung_detector_suspended = true; 366 break; 367 case PM_POST_SUSPEND: 368 case PM_POST_HIBERNATION: 369 case PM_POST_RESTORE: 370 hung_detector_suspended = false; 371 break; 372 default: 373 break; 374 } 375 return NOTIFY_OK; 376 } 377 378 /* 379 * kthread which checks for tasks stuck in D state 380 */ 381 static int watchdog(void *dummy) 382 { 383 unsigned long hung_last_checked = jiffies; 384 385 set_user_nice(current, 0); 386 387 for ( ; ; ) { 388 unsigned long timeout = sysctl_hung_task_timeout_secs; 389 unsigned long interval = sysctl_hung_task_check_interval_secs; 390 long t; 391 392 if (interval == 0) 393 interval = timeout; 394 interval = min_t(unsigned long, interval, timeout); 395 t = hung_timeout_jiffies(hung_last_checked, interval); 396 if (t <= 0) { 397 if (!atomic_xchg(&reset_hung_task, 0) && 398 !hung_detector_suspended) 399 check_hung_uninterruptible_tasks(timeout); 400 hung_last_checked = jiffies; 401 continue; 402 } 403 schedule_timeout_interruptible(t); 404 } 405 406 return 0; 407 } 408 409 static int __init hung_task_init(void) 410 { 411 atomic_notifier_chain_register(&panic_notifier_list, &panic_block); 412 413 /* Disable hung task detector on suspend */ 414 pm_notifier(hungtask_pm_notify, 0); 415 416 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd"); 417 hung_task_sysctl_init(); 418 419 return 0; 420 } 421 subsys_initcall(hung_task_init); 422