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 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 47 /* 48 * Zero (default value) means use sysctl_hung_task_timeout_secs: 49 */ 50 unsigned long __read_mostly sysctl_hung_task_check_interval_secs; 51 52 int __read_mostly sysctl_hung_task_warnings = 10; 53 54 static int __read_mostly did_panic; 55 static bool hung_task_show_lock; 56 static bool hung_task_call_panic; 57 static bool hung_task_show_all_bt; 58 59 static struct task_struct *watchdog_task; 60 61 #ifdef CONFIG_SMP 62 /* 63 * Should we dump all CPUs backtraces in a hung task event? 64 * Defaults to 0, can be changed via sysctl. 65 */ 66 static unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace; 67 #else 68 #define sysctl_hung_task_all_cpu_backtrace 0 69 #endif /* CONFIG_SMP */ 70 71 /* 72 * Should we panic (and reboot, if panic_timeout= is set) when a 73 * hung task is detected: 74 */ 75 unsigned int __read_mostly sysctl_hung_task_panic = 76 IS_ENABLED(CONFIG_BOOTPARAM_HUNG_TASK_PANIC); 77 78 static int 79 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr) 80 { 81 did_panic = 1; 82 83 return NOTIFY_DONE; 84 } 85 86 static struct notifier_block panic_block = { 87 .notifier_call = hung_task_panic, 88 }; 89 90 static void check_hung_task(struct task_struct *t, unsigned long timeout) 91 { 92 unsigned long switch_count = t->nvcsw + t->nivcsw; 93 94 /* 95 * Ensure the task is not frozen. 96 * Also, skip vfork and any other user process that freezer should skip. 97 */ 98 if (unlikely(READ_ONCE(t->__state) & TASK_FROZEN)) 99 return; 100 101 /* 102 * When a freshly created task is scheduled once, changes its state to 103 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it 104 * musn't be checked. 105 */ 106 if (unlikely(!switch_count)) 107 return; 108 109 if (switch_count != t->last_switch_count) { 110 t->last_switch_count = switch_count; 111 t->last_switch_time = jiffies; 112 return; 113 } 114 if (time_is_after_jiffies(t->last_switch_time + timeout * HZ)) 115 return; 116 117 trace_sched_process_hang(t); 118 119 if (sysctl_hung_task_panic) { 120 console_verbose(); 121 hung_task_show_lock = true; 122 hung_task_call_panic = true; 123 } 124 125 /* 126 * Ok, the task did not get scheduled for more than 2 minutes, 127 * complain: 128 */ 129 if (sysctl_hung_task_warnings) { 130 if (sysctl_hung_task_warnings > 0) 131 sysctl_hung_task_warnings--; 132 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n", 133 t->comm, t->pid, (jiffies - t->last_switch_time) / HZ); 134 pr_err(" %s %s %.*s\n", 135 print_tainted(), init_utsname()->release, 136 (int)strcspn(init_utsname()->version, " "), 137 init_utsname()->version); 138 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\"" 139 " disables this message.\n"); 140 sched_show_task(t); 141 hung_task_show_lock = true; 142 143 if (sysctl_hung_task_all_cpu_backtrace) 144 hung_task_show_all_bt = true; 145 } 146 147 touch_nmi_watchdog(); 148 } 149 150 /* 151 * To avoid extending the RCU grace period for an unbounded amount of time, 152 * periodically exit the critical section and enter a new one. 153 * 154 * For preemptible RCU it is sufficient to call rcu_read_unlock in order 155 * to exit the grace period. For classic RCU, a reschedule is required. 156 */ 157 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t) 158 { 159 bool can_cont; 160 161 get_task_struct(g); 162 get_task_struct(t); 163 rcu_read_unlock(); 164 cond_resched(); 165 rcu_read_lock(); 166 can_cont = pid_alive(g) && pid_alive(t); 167 put_task_struct(t); 168 put_task_struct(g); 169 170 return can_cont; 171 } 172 173 /* 174 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for 175 * a really long time (120 seconds). If that happens, print out 176 * a warning. 177 */ 178 static void check_hung_uninterruptible_tasks(unsigned long timeout) 179 { 180 int max_count = sysctl_hung_task_check_count; 181 unsigned long last_break = jiffies; 182 struct task_struct *g, *t; 183 184 /* 185 * If the system crashed already then all bets are off, 186 * do not report extra hung tasks: 187 */ 188 if (test_taint(TAINT_DIE) || did_panic) 189 return; 190 191 hung_task_show_lock = false; 192 rcu_read_lock(); 193 for_each_process_thread(g, t) { 194 unsigned int state; 195 196 if (!max_count--) 197 goto unlock; 198 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) { 199 if (!rcu_lock_break(g, t)) 200 goto unlock; 201 last_break = jiffies; 202 } 203 /* 204 * skip the TASK_KILLABLE tasks -- these can be killed 205 * skip the TASK_IDLE tasks -- those are genuinely idle 206 */ 207 state = READ_ONCE(t->__state); 208 if ((state & TASK_UNINTERRUPTIBLE) && 209 !(state & TASK_WAKEKILL) && 210 !(state & TASK_NOLOAD)) 211 check_hung_task(t, timeout); 212 } 213 unlock: 214 rcu_read_unlock(); 215 if (hung_task_show_lock) 216 debug_show_all_locks(); 217 218 if (hung_task_show_all_bt) { 219 hung_task_show_all_bt = false; 220 trigger_all_cpu_backtrace(); 221 } 222 223 if (hung_task_call_panic) 224 panic("hung_task: blocked tasks"); 225 } 226 227 static long hung_timeout_jiffies(unsigned long last_checked, 228 unsigned long timeout) 229 { 230 /* timeout of 0 will disable the watchdog */ 231 return timeout ? last_checked - jiffies + timeout * HZ : 232 MAX_SCHEDULE_TIMEOUT; 233 } 234 235 #ifdef CONFIG_SYSCTL 236 /* 237 * Process updating of timeout sysctl 238 */ 239 static int proc_dohung_task_timeout_secs(struct ctl_table *table, int write, 240 void *buffer, 241 size_t *lenp, loff_t *ppos) 242 { 243 int ret; 244 245 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); 246 247 if (ret || !write) 248 goto out; 249 250 wake_up_process(watchdog_task); 251 252 out: 253 return ret; 254 } 255 256 /* 257 * This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs 258 * and hung_task_check_interval_secs 259 */ 260 static const unsigned long hung_task_timeout_max = (LONG_MAX / HZ); 261 static struct ctl_table hung_task_sysctls[] = { 262 #ifdef CONFIG_SMP 263 { 264 .procname = "hung_task_all_cpu_backtrace", 265 .data = &sysctl_hung_task_all_cpu_backtrace, 266 .maxlen = sizeof(int), 267 .mode = 0644, 268 .proc_handler = proc_dointvec_minmax, 269 .extra1 = SYSCTL_ZERO, 270 .extra2 = SYSCTL_ONE, 271 }, 272 #endif /* CONFIG_SMP */ 273 { 274 .procname = "hung_task_panic", 275 .data = &sysctl_hung_task_panic, 276 .maxlen = sizeof(int), 277 .mode = 0644, 278 .proc_handler = proc_dointvec_minmax, 279 .extra1 = SYSCTL_ZERO, 280 .extra2 = SYSCTL_ONE, 281 }, 282 { 283 .procname = "hung_task_check_count", 284 .data = &sysctl_hung_task_check_count, 285 .maxlen = sizeof(int), 286 .mode = 0644, 287 .proc_handler = proc_dointvec_minmax, 288 .extra1 = SYSCTL_ZERO, 289 }, 290 { 291 .procname = "hung_task_timeout_secs", 292 .data = &sysctl_hung_task_timeout_secs, 293 .maxlen = sizeof(unsigned long), 294 .mode = 0644, 295 .proc_handler = proc_dohung_task_timeout_secs, 296 .extra2 = (void *)&hung_task_timeout_max, 297 }, 298 { 299 .procname = "hung_task_check_interval_secs", 300 .data = &sysctl_hung_task_check_interval_secs, 301 .maxlen = sizeof(unsigned long), 302 .mode = 0644, 303 .proc_handler = proc_dohung_task_timeout_secs, 304 .extra2 = (void *)&hung_task_timeout_max, 305 }, 306 { 307 .procname = "hung_task_warnings", 308 .data = &sysctl_hung_task_warnings, 309 .maxlen = sizeof(int), 310 .mode = 0644, 311 .proc_handler = proc_dointvec_minmax, 312 .extra1 = SYSCTL_NEG_ONE, 313 }, 314 {} 315 }; 316 317 static void __init hung_task_sysctl_init(void) 318 { 319 register_sysctl_init("kernel", hung_task_sysctls); 320 } 321 #else 322 #define hung_task_sysctl_init() do { } while (0) 323 #endif /* CONFIG_SYSCTL */ 324 325 326 static atomic_t reset_hung_task = ATOMIC_INIT(0); 327 328 void reset_hung_task_detector(void) 329 { 330 atomic_set(&reset_hung_task, 1); 331 } 332 EXPORT_SYMBOL_GPL(reset_hung_task_detector); 333 334 static bool hung_detector_suspended; 335 336 static int hungtask_pm_notify(struct notifier_block *self, 337 unsigned long action, void *hcpu) 338 { 339 switch (action) { 340 case PM_SUSPEND_PREPARE: 341 case PM_HIBERNATION_PREPARE: 342 case PM_RESTORE_PREPARE: 343 hung_detector_suspended = true; 344 break; 345 case PM_POST_SUSPEND: 346 case PM_POST_HIBERNATION: 347 case PM_POST_RESTORE: 348 hung_detector_suspended = false; 349 break; 350 default: 351 break; 352 } 353 return NOTIFY_OK; 354 } 355 356 /* 357 * kthread which checks for tasks stuck in D state 358 */ 359 static int watchdog(void *dummy) 360 { 361 unsigned long hung_last_checked = jiffies; 362 363 set_user_nice(current, 0); 364 365 for ( ; ; ) { 366 unsigned long timeout = sysctl_hung_task_timeout_secs; 367 unsigned long interval = sysctl_hung_task_check_interval_secs; 368 long t; 369 370 if (interval == 0) 371 interval = timeout; 372 interval = min_t(unsigned long, interval, timeout); 373 t = hung_timeout_jiffies(hung_last_checked, interval); 374 if (t <= 0) { 375 if (!atomic_xchg(&reset_hung_task, 0) && 376 !hung_detector_suspended) 377 check_hung_uninterruptible_tasks(timeout); 378 hung_last_checked = jiffies; 379 continue; 380 } 381 schedule_timeout_interruptible(t); 382 } 383 384 return 0; 385 } 386 387 static int __init hung_task_init(void) 388 { 389 atomic_notifier_chain_register(&panic_notifier_list, &panic_block); 390 391 /* Disable hung task detector on suspend */ 392 pm_notifier(hungtask_pm_notify, 0); 393 394 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd"); 395 hung_task_sysctl_init(); 396 397 return 0; 398 } 399 subsys_initcall(hung_task_init); 400