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 67 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr) 68 { 69 did_panic = 1; 70 71 return NOTIFY_DONE; 72 } 73 74 static struct notifier_block panic_block = { 75 .notifier_call = hung_task_panic, 76 }; 77 78 static void check_hung_task(struct task_struct *t, unsigned long timeout) 79 { 80 unsigned long switch_count = t->nvcsw + t->nivcsw; 81 82 /* 83 * Ensure the task is not frozen. 84 * Also, skip vfork and any other user process that freezer should skip. 85 */ 86 if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP))) 87 return; 88 89 /* 90 * When a freshly created task is scheduled once, changes its state to 91 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it 92 * musn't be checked. 93 */ 94 if (unlikely(!switch_count)) 95 return; 96 97 if (switch_count != t->last_switch_count) { 98 t->last_switch_count = switch_count; 99 t->last_switch_time = jiffies; 100 return; 101 } 102 if (time_is_after_jiffies(t->last_switch_time + timeout * HZ)) 103 return; 104 105 trace_sched_process_hang(t); 106 107 if (sysctl_hung_task_panic) { 108 console_verbose(); 109 hung_task_show_lock = true; 110 hung_task_call_panic = true; 111 } 112 113 /* 114 * Ok, the task did not get scheduled for more than 2 minutes, 115 * complain: 116 */ 117 if (sysctl_hung_task_warnings) { 118 if (sysctl_hung_task_warnings > 0) 119 sysctl_hung_task_warnings--; 120 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n", 121 t->comm, t->pid, (jiffies - t->last_switch_time) / HZ); 122 pr_err(" %s %s %.*s\n", 123 print_tainted(), init_utsname()->release, 124 (int)strcspn(init_utsname()->version, " "), 125 init_utsname()->version); 126 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\"" 127 " disables this message.\n"); 128 sched_show_task(t); 129 hung_task_show_lock = true; 130 } 131 132 touch_nmi_watchdog(); 133 } 134 135 /* 136 * To avoid extending the RCU grace period for an unbounded amount of time, 137 * periodically exit the critical section and enter a new one. 138 * 139 * For preemptible RCU it is sufficient to call rcu_read_unlock in order 140 * to exit the grace period. For classic RCU, a reschedule is required. 141 */ 142 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t) 143 { 144 bool can_cont; 145 146 get_task_struct(g); 147 get_task_struct(t); 148 rcu_read_unlock(); 149 cond_resched(); 150 rcu_read_lock(); 151 can_cont = pid_alive(g) && pid_alive(t); 152 put_task_struct(t); 153 put_task_struct(g); 154 155 return can_cont; 156 } 157 158 /* 159 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for 160 * a really long time (120 seconds). If that happens, print out 161 * a warning. 162 */ 163 static void check_hung_uninterruptible_tasks(unsigned long timeout) 164 { 165 int max_count = sysctl_hung_task_check_count; 166 unsigned long last_break = jiffies; 167 struct task_struct *g, *t; 168 169 /* 170 * If the system crashed already then all bets are off, 171 * do not report extra hung tasks: 172 */ 173 if (test_taint(TAINT_DIE) || did_panic) 174 return; 175 176 hung_task_show_lock = false; 177 rcu_read_lock(); 178 for_each_process_thread(g, t) { 179 if (!max_count--) 180 goto unlock; 181 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) { 182 if (!rcu_lock_break(g, t)) 183 goto unlock; 184 last_break = jiffies; 185 } 186 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */ 187 if (t->state == TASK_UNINTERRUPTIBLE) 188 check_hung_task(t, timeout); 189 } 190 unlock: 191 rcu_read_unlock(); 192 if (hung_task_show_lock) 193 debug_show_all_locks(); 194 if (hung_task_call_panic) { 195 trigger_all_cpu_backtrace(); 196 panic("hung_task: blocked tasks"); 197 } 198 } 199 200 static long hung_timeout_jiffies(unsigned long last_checked, 201 unsigned long timeout) 202 { 203 /* timeout of 0 will disable the watchdog */ 204 return timeout ? last_checked - jiffies + timeout * HZ : 205 MAX_SCHEDULE_TIMEOUT; 206 } 207 208 /* 209 * Process updating of timeout sysctl 210 */ 211 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write, 212 void __user *buffer, 213 size_t *lenp, loff_t *ppos) 214 { 215 int ret; 216 217 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); 218 219 if (ret || !write) 220 goto out; 221 222 wake_up_process(watchdog_task); 223 224 out: 225 return ret; 226 } 227 228 static atomic_t reset_hung_task = ATOMIC_INIT(0); 229 230 void reset_hung_task_detector(void) 231 { 232 atomic_set(&reset_hung_task, 1); 233 } 234 EXPORT_SYMBOL_GPL(reset_hung_task_detector); 235 236 static bool hung_detector_suspended; 237 238 static int hungtask_pm_notify(struct notifier_block *self, 239 unsigned long action, void *hcpu) 240 { 241 switch (action) { 242 case PM_SUSPEND_PREPARE: 243 case PM_HIBERNATION_PREPARE: 244 case PM_RESTORE_PREPARE: 245 hung_detector_suspended = true; 246 break; 247 case PM_POST_SUSPEND: 248 case PM_POST_HIBERNATION: 249 case PM_POST_RESTORE: 250 hung_detector_suspended = false; 251 break; 252 default: 253 break; 254 } 255 return NOTIFY_OK; 256 } 257 258 /* 259 * kthread which checks for tasks stuck in D state 260 */ 261 static int watchdog(void *dummy) 262 { 263 unsigned long hung_last_checked = jiffies; 264 265 set_user_nice(current, 0); 266 267 for ( ; ; ) { 268 unsigned long timeout = sysctl_hung_task_timeout_secs; 269 unsigned long interval = sysctl_hung_task_check_interval_secs; 270 long t; 271 272 if (interval == 0) 273 interval = timeout; 274 interval = min_t(unsigned long, interval, timeout); 275 t = hung_timeout_jiffies(hung_last_checked, interval); 276 if (t <= 0) { 277 if (!atomic_xchg(&reset_hung_task, 0) && 278 !hung_detector_suspended) 279 check_hung_uninterruptible_tasks(timeout); 280 hung_last_checked = jiffies; 281 continue; 282 } 283 schedule_timeout_interruptible(t); 284 } 285 286 return 0; 287 } 288 289 static int __init hung_task_init(void) 290 { 291 atomic_notifier_chain_register(&panic_notifier_list, &panic_block); 292 293 /* Disable hung task detector on suspend */ 294 pm_notifier(hungtask_pm_notify, 0); 295 296 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd"); 297 298 return 0; 299 } 300 subsys_initcall(hung_task_init); 301