1 /* 2 * Detect Hung Task 3 * 4 * kernel/hung_task.c - kernel thread for detecting tasks stuck in D state 5 * 6 */ 7 8 #include <linux/mm.h> 9 #include <linux/cpu.h> 10 #include <linux/nmi.h> 11 #include <linux/init.h> 12 #include <linux/delay.h> 13 #include <linux/freezer.h> 14 #include <linux/kthread.h> 15 #include <linux/lockdep.h> 16 #include <linux/export.h> 17 #include <linux/sysctl.h> 18 #include <linux/suspend.h> 19 #include <linux/utsname.h> 20 #include <linux/sched/signal.h> 21 #include <linux/sched/debug.h> 22 #include <linux/sched/sysctl.h> 23 24 #include <trace/events/sched.h> 25 26 /* 27 * The number of tasks checked: 28 */ 29 int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT; 30 31 /* 32 * Limit number of tasks checked in a batch. 33 * 34 * This value controls the preemptibility of khungtaskd since preemption 35 * is disabled during the critical section. It also controls the size of 36 * the RCU grace period. So it needs to be upper-bound. 37 */ 38 #define HUNG_TASK_LOCK_BREAK (HZ / 10) 39 40 /* 41 * Zero means infinite timeout - no checking done: 42 */ 43 unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT; 44 45 /* 46 * Zero (default value) means use sysctl_hung_task_timeout_secs: 47 */ 48 unsigned long __read_mostly sysctl_hung_task_check_interval_secs; 49 50 int __read_mostly sysctl_hung_task_warnings = 10; 51 52 static int __read_mostly did_panic; 53 static bool hung_task_show_lock; 54 static bool hung_task_call_panic; 55 56 static struct task_struct *watchdog_task; 57 58 /* 59 * Should we panic (and reboot, if panic_timeout= is set) when a 60 * hung task is detected: 61 */ 62 unsigned int __read_mostly sysctl_hung_task_panic = 63 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE; 64 65 static int __init hung_task_panic_setup(char *str) 66 { 67 int rc = kstrtouint(str, 0, &sysctl_hung_task_panic); 68 69 if (rc) 70 return rc; 71 return 1; 72 } 73 __setup("hung_task_panic=", hung_task_panic_setup); 74 75 static int 76 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr) 77 { 78 did_panic = 1; 79 80 return NOTIFY_DONE; 81 } 82 83 static struct notifier_block panic_block = { 84 .notifier_call = hung_task_panic, 85 }; 86 87 static void check_hung_task(struct task_struct *t, unsigned long timeout) 88 { 89 unsigned long switch_count = t->nvcsw + t->nivcsw; 90 91 /* 92 * Ensure the task is not frozen. 93 * Also, skip vfork and any other user process that freezer should skip. 94 */ 95 if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP))) 96 return; 97 98 /* 99 * When a freshly created task is scheduled once, changes its state to 100 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it 101 * musn't be checked. 102 */ 103 if (unlikely(!switch_count)) 104 return; 105 106 if (switch_count != t->last_switch_count) { 107 t->last_switch_count = switch_count; 108 t->last_switch_time = jiffies; 109 return; 110 } 111 if (time_is_after_jiffies(t->last_switch_time + timeout * HZ)) 112 return; 113 114 trace_sched_process_hang(t); 115 116 if (sysctl_hung_task_panic) { 117 console_verbose(); 118 hung_task_show_lock = true; 119 hung_task_call_panic = true; 120 } 121 122 /* 123 * Ok, the task did not get scheduled for more than 2 minutes, 124 * complain: 125 */ 126 if (sysctl_hung_task_warnings) { 127 if (sysctl_hung_task_warnings > 0) 128 sysctl_hung_task_warnings--; 129 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n", 130 t->comm, t->pid, (jiffies - t->last_switch_time) / HZ); 131 pr_err(" %s %s %.*s\n", 132 print_tainted(), init_utsname()->release, 133 (int)strcspn(init_utsname()->version, " "), 134 init_utsname()->version); 135 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\"" 136 " disables this message.\n"); 137 sched_show_task(t); 138 hung_task_show_lock = true; 139 } 140 141 touch_nmi_watchdog(); 142 } 143 144 /* 145 * To avoid extending the RCU grace period for an unbounded amount of time, 146 * periodically exit the critical section and enter a new one. 147 * 148 * For preemptible RCU it is sufficient to call rcu_read_unlock in order 149 * to exit the grace period. For classic RCU, a reschedule is required. 150 */ 151 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t) 152 { 153 bool can_cont; 154 155 get_task_struct(g); 156 get_task_struct(t); 157 rcu_read_unlock(); 158 cond_resched(); 159 rcu_read_lock(); 160 can_cont = pid_alive(g) && pid_alive(t); 161 put_task_struct(t); 162 put_task_struct(g); 163 164 return can_cont; 165 } 166 167 /* 168 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for 169 * a really long time (120 seconds). If that happens, print out 170 * a warning. 171 */ 172 static void check_hung_uninterruptible_tasks(unsigned long timeout) 173 { 174 int max_count = sysctl_hung_task_check_count; 175 unsigned long last_break = jiffies; 176 struct task_struct *g, *t; 177 178 /* 179 * If the system crashed already then all bets are off, 180 * do not report extra hung tasks: 181 */ 182 if (test_taint(TAINT_DIE) || did_panic) 183 return; 184 185 hung_task_show_lock = false; 186 rcu_read_lock(); 187 for_each_process_thread(g, t) { 188 if (!max_count--) 189 goto unlock; 190 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) { 191 if (!rcu_lock_break(g, t)) 192 goto unlock; 193 last_break = jiffies; 194 } 195 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */ 196 if (t->state == TASK_UNINTERRUPTIBLE) 197 check_hung_task(t, timeout); 198 } 199 unlock: 200 rcu_read_unlock(); 201 if (hung_task_show_lock) 202 debug_show_all_locks(); 203 if (hung_task_call_panic) { 204 trigger_all_cpu_backtrace(); 205 panic("hung_task: blocked tasks"); 206 } 207 } 208 209 static long hung_timeout_jiffies(unsigned long last_checked, 210 unsigned long timeout) 211 { 212 /* timeout of 0 will disable the watchdog */ 213 return timeout ? last_checked - jiffies + timeout * HZ : 214 MAX_SCHEDULE_TIMEOUT; 215 } 216 217 /* 218 * Process updating of timeout sysctl 219 */ 220 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write, 221 void __user *buffer, 222 size_t *lenp, loff_t *ppos) 223 { 224 int ret; 225 226 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); 227 228 if (ret || !write) 229 goto out; 230 231 wake_up_process(watchdog_task); 232 233 out: 234 return ret; 235 } 236 237 static atomic_t reset_hung_task = ATOMIC_INIT(0); 238 239 void reset_hung_task_detector(void) 240 { 241 atomic_set(&reset_hung_task, 1); 242 } 243 EXPORT_SYMBOL_GPL(reset_hung_task_detector); 244 245 static bool hung_detector_suspended; 246 247 static int hungtask_pm_notify(struct notifier_block *self, 248 unsigned long action, void *hcpu) 249 { 250 switch (action) { 251 case PM_SUSPEND_PREPARE: 252 case PM_HIBERNATION_PREPARE: 253 case PM_RESTORE_PREPARE: 254 hung_detector_suspended = true; 255 break; 256 case PM_POST_SUSPEND: 257 case PM_POST_HIBERNATION: 258 case PM_POST_RESTORE: 259 hung_detector_suspended = false; 260 break; 261 default: 262 break; 263 } 264 return NOTIFY_OK; 265 } 266 267 /* 268 * kthread which checks for tasks stuck in D state 269 */ 270 static int watchdog(void *dummy) 271 { 272 unsigned long hung_last_checked = jiffies; 273 274 set_user_nice(current, 0); 275 276 for ( ; ; ) { 277 unsigned long timeout = sysctl_hung_task_timeout_secs; 278 unsigned long interval = sysctl_hung_task_check_interval_secs; 279 long t; 280 281 if (interval == 0) 282 interval = timeout; 283 interval = min_t(unsigned long, interval, timeout); 284 t = hung_timeout_jiffies(hung_last_checked, interval); 285 if (t <= 0) { 286 if (!atomic_xchg(&reset_hung_task, 0) && 287 !hung_detector_suspended) 288 check_hung_uninterruptible_tasks(timeout); 289 hung_last_checked = jiffies; 290 continue; 291 } 292 schedule_timeout_interruptible(t); 293 } 294 295 return 0; 296 } 297 298 static int __init hung_task_init(void) 299 { 300 atomic_notifier_chain_register(&panic_notifier_list, &panic_block); 301 302 /* Disable hung task detector on suspend */ 303 pm_notifier(hungtask_pm_notify, 0); 304 305 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd"); 306 307 return 0; 308 } 309 subsys_initcall(hung_task_init); 310