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/sysctl.h> 19 #include <linux/suspend.h> 20 #include <linux/utsname.h> 21 #include <linux/sched/signal.h> 22 #include <linux/sched/debug.h> 23 #include <linux/sched/sysctl.h> 24 25 #include <trace/events/sched.h> 26 27 /* 28 * The number of tasks checked: 29 */ 30 int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT; 31 32 /* 33 * Limit number of tasks checked in a batch. 34 * 35 * This value controls the preemptibility of khungtaskd since preemption 36 * is disabled during the critical section. It also controls the size of 37 * the RCU grace period. So it needs to be upper-bound. 38 */ 39 #define HUNG_TASK_LOCK_BREAK (HZ / 10) 40 41 /* 42 * Zero means infinite timeout - no checking done: 43 */ 44 unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT; 45 46 /* 47 * Zero (default value) means use sysctl_hung_task_timeout_secs: 48 */ 49 unsigned long __read_mostly sysctl_hung_task_check_interval_secs; 50 51 int __read_mostly sysctl_hung_task_warnings = 10; 52 53 static int __read_mostly did_panic; 54 static bool hung_task_show_lock; 55 static bool hung_task_call_panic; 56 57 static struct task_struct *watchdog_task; 58 59 /* 60 * Should we panic (and reboot, if panic_timeout= is set) when a 61 * hung task is detected: 62 */ 63 unsigned int __read_mostly sysctl_hung_task_panic = 64 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE; 65 66 static int __init hung_task_panic_setup(char *str) 67 { 68 int rc = kstrtouint(str, 0, &sysctl_hung_task_panic); 69 70 if (rc) 71 return rc; 72 return 1; 73 } 74 __setup("hung_task_panic=", hung_task_panic_setup); 75 76 static int 77 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr) 78 { 79 did_panic = 1; 80 81 return NOTIFY_DONE; 82 } 83 84 static struct notifier_block panic_block = { 85 .notifier_call = hung_task_panic, 86 }; 87 88 static void check_hung_task(struct task_struct *t, unsigned long timeout) 89 { 90 unsigned long switch_count = t->nvcsw + t->nivcsw; 91 92 /* 93 * Ensure the task is not frozen. 94 * Also, skip vfork and any other user process that freezer should skip. 95 */ 96 if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP))) 97 return; 98 99 /* 100 * When a freshly created task is scheduled once, changes its state to 101 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it 102 * musn't be checked. 103 */ 104 if (unlikely(!switch_count)) 105 return; 106 107 if (switch_count != t->last_switch_count) { 108 t->last_switch_count = switch_count; 109 t->last_switch_time = jiffies; 110 return; 111 } 112 if (time_is_after_jiffies(t->last_switch_time + timeout * HZ)) 113 return; 114 115 trace_sched_process_hang(t); 116 117 if (sysctl_hung_task_panic) { 118 console_verbose(); 119 hung_task_show_lock = true; 120 hung_task_call_panic = true; 121 } 122 123 /* 124 * Ok, the task did not get scheduled for more than 2 minutes, 125 * complain: 126 */ 127 if (sysctl_hung_task_warnings) { 128 if (sysctl_hung_task_warnings > 0) 129 sysctl_hung_task_warnings--; 130 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n", 131 t->comm, t->pid, (jiffies - t->last_switch_time) / HZ); 132 pr_err(" %s %s %.*s\n", 133 print_tainted(), init_utsname()->release, 134 (int)strcspn(init_utsname()->version, " "), 135 init_utsname()->version); 136 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\"" 137 " disables this message.\n"); 138 sched_show_task(t); 139 hung_task_show_lock = true; 140 } 141 142 touch_nmi_watchdog(); 143 } 144 145 /* 146 * To avoid extending the RCU grace period for an unbounded amount of time, 147 * periodically exit the critical section and enter a new one. 148 * 149 * For preemptible RCU it is sufficient to call rcu_read_unlock in order 150 * to exit the grace period. For classic RCU, a reschedule is required. 151 */ 152 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t) 153 { 154 bool can_cont; 155 156 get_task_struct(g); 157 get_task_struct(t); 158 rcu_read_unlock(); 159 cond_resched(); 160 rcu_read_lock(); 161 can_cont = pid_alive(g) && pid_alive(t); 162 put_task_struct(t); 163 put_task_struct(g); 164 165 return can_cont; 166 } 167 168 /* 169 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for 170 * a really long time (120 seconds). If that happens, print out 171 * a warning. 172 */ 173 static void check_hung_uninterruptible_tasks(unsigned long timeout) 174 { 175 int max_count = sysctl_hung_task_check_count; 176 unsigned long last_break = jiffies; 177 struct task_struct *g, *t; 178 179 /* 180 * If the system crashed already then all bets are off, 181 * do not report extra hung tasks: 182 */ 183 if (test_taint(TAINT_DIE) || did_panic) 184 return; 185 186 hung_task_show_lock = false; 187 rcu_read_lock(); 188 for_each_process_thread(g, t) { 189 if (!max_count--) 190 goto unlock; 191 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) { 192 if (!rcu_lock_break(g, t)) 193 goto unlock; 194 last_break = jiffies; 195 } 196 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */ 197 if (t->state == TASK_UNINTERRUPTIBLE) 198 check_hung_task(t, timeout); 199 } 200 unlock: 201 rcu_read_unlock(); 202 if (hung_task_show_lock) 203 debug_show_all_locks(); 204 if (hung_task_call_panic) { 205 trigger_all_cpu_backtrace(); 206 panic("hung_task: blocked tasks"); 207 } 208 } 209 210 static long hung_timeout_jiffies(unsigned long last_checked, 211 unsigned long timeout) 212 { 213 /* timeout of 0 will disable the watchdog */ 214 return timeout ? last_checked - jiffies + timeout * HZ : 215 MAX_SCHEDULE_TIMEOUT; 216 } 217 218 /* 219 * Process updating of timeout sysctl 220 */ 221 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write, 222 void __user *buffer, 223 size_t *lenp, loff_t *ppos) 224 { 225 int ret; 226 227 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); 228 229 if (ret || !write) 230 goto out; 231 232 wake_up_process(watchdog_task); 233 234 out: 235 return ret; 236 } 237 238 static atomic_t reset_hung_task = ATOMIC_INIT(0); 239 240 void reset_hung_task_detector(void) 241 { 242 atomic_set(&reset_hung_task, 1); 243 } 244 EXPORT_SYMBOL_GPL(reset_hung_task_detector); 245 246 static bool hung_detector_suspended; 247 248 static int hungtask_pm_notify(struct notifier_block *self, 249 unsigned long action, void *hcpu) 250 { 251 switch (action) { 252 case PM_SUSPEND_PREPARE: 253 case PM_HIBERNATION_PREPARE: 254 case PM_RESTORE_PREPARE: 255 hung_detector_suspended = true; 256 break; 257 case PM_POST_SUSPEND: 258 case PM_POST_HIBERNATION: 259 case PM_POST_RESTORE: 260 hung_detector_suspended = false; 261 break; 262 default: 263 break; 264 } 265 return NOTIFY_OK; 266 } 267 268 /* 269 * kthread which checks for tasks stuck in D state 270 */ 271 static int watchdog(void *dummy) 272 { 273 unsigned long hung_last_checked = jiffies; 274 275 set_user_nice(current, 0); 276 277 for ( ; ; ) { 278 unsigned long timeout = sysctl_hung_task_timeout_secs; 279 unsigned long interval = sysctl_hung_task_check_interval_secs; 280 long t; 281 282 if (interval == 0) 283 interval = timeout; 284 interval = min_t(unsigned long, interval, timeout); 285 t = hung_timeout_jiffies(hung_last_checked, interval); 286 if (t <= 0) { 287 if (!atomic_xchg(&reset_hung_task, 0) && 288 !hung_detector_suspended) 289 check_hung_uninterruptible_tasks(timeout); 290 hung_last_checked = jiffies; 291 continue; 292 } 293 schedule_timeout_interruptible(t); 294 } 295 296 return 0; 297 } 298 299 static int __init hung_task_init(void) 300 { 301 atomic_notifier_chain_register(&panic_notifier_list, &panic_block); 302 303 /* Disable hung task detector on suspend */ 304 pm_notifier(hungtask_pm_notify, 0); 305 306 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd"); 307 308 return 0; 309 } 310 subsys_initcall(hung_task_init); 311