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