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/utsname.h> 19 #include <linux/sched/signal.h> 20 #include <linux/sched/debug.h> 21 22 #include <trace/events/sched.h> 23 24 /* 25 * The number of tasks checked: 26 */ 27 int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT; 28 29 /* 30 * Limit number of tasks checked in a batch. 31 * 32 * This value controls the preemptibility of khungtaskd since preemption 33 * is disabled during the critical section. It also controls the size of 34 * the RCU grace period. So it needs to be upper-bound. 35 */ 36 #define HUNG_TASK_BATCHING 1024 37 38 /* 39 * Zero means infinite timeout - no checking done: 40 */ 41 unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT; 42 43 int __read_mostly sysctl_hung_task_warnings = 10; 44 45 static int __read_mostly did_panic; 46 static bool hung_task_show_lock; 47 static bool hung_task_call_panic; 48 49 static struct task_struct *watchdog_task; 50 51 /* 52 * Should we panic (and reboot, if panic_timeout= is set) when a 53 * hung task is detected: 54 */ 55 unsigned int __read_mostly sysctl_hung_task_panic = 56 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE; 57 58 static int __init hung_task_panic_setup(char *str) 59 { 60 int rc = kstrtouint(str, 0, &sysctl_hung_task_panic); 61 62 if (rc) 63 return rc; 64 return 1; 65 } 66 __setup("hung_task_panic=", hung_task_panic_setup); 67 68 static int 69 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr) 70 { 71 did_panic = 1; 72 73 return NOTIFY_DONE; 74 } 75 76 static struct notifier_block panic_block = { 77 .notifier_call = hung_task_panic, 78 }; 79 80 static void check_hung_task(struct task_struct *t, unsigned long timeout) 81 { 82 unsigned long switch_count = t->nvcsw + t->nivcsw; 83 84 /* 85 * Ensure the task is not frozen. 86 * Also, skip vfork and any other user process that freezer should skip. 87 */ 88 if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP))) 89 return; 90 91 /* 92 * When a freshly created task is scheduled once, changes its state to 93 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it 94 * musn't be checked. 95 */ 96 if (unlikely(!switch_count)) 97 return; 98 99 if (switch_count != t->last_switch_count) { 100 t->last_switch_count = switch_count; 101 return; 102 } 103 104 trace_sched_process_hang(t); 105 106 if (!sysctl_hung_task_warnings && !sysctl_hung_task_panic) 107 return; 108 109 /* 110 * Ok, the task did not get scheduled for more than 2 minutes, 111 * complain: 112 */ 113 if (sysctl_hung_task_warnings) { 114 if (sysctl_hung_task_warnings > 0) 115 sysctl_hung_task_warnings--; 116 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n", 117 t->comm, t->pid, timeout); 118 pr_err(" %s %s %.*s\n", 119 print_tainted(), init_utsname()->release, 120 (int)strcspn(init_utsname()->version, " "), 121 init_utsname()->version); 122 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\"" 123 " disables this message.\n"); 124 sched_show_task(t); 125 hung_task_show_lock = true; 126 } 127 128 touch_nmi_watchdog(); 129 130 if (sysctl_hung_task_panic) { 131 hung_task_show_lock = true; 132 hung_task_call_panic = true; 133 } 134 } 135 136 /* 137 * To avoid extending the RCU grace period for an unbounded amount of time, 138 * periodically exit the critical section and enter a new one. 139 * 140 * For preemptible RCU it is sufficient to call rcu_read_unlock in order 141 * to exit the grace period. For classic RCU, a reschedule is required. 142 */ 143 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t) 144 { 145 bool can_cont; 146 147 get_task_struct(g); 148 get_task_struct(t); 149 rcu_read_unlock(); 150 cond_resched(); 151 rcu_read_lock(); 152 can_cont = pid_alive(g) && pid_alive(t); 153 put_task_struct(t); 154 put_task_struct(g); 155 156 return can_cont; 157 } 158 159 /* 160 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for 161 * a really long time (120 seconds). If that happens, print out 162 * a warning. 163 */ 164 static void check_hung_uninterruptible_tasks(unsigned long timeout) 165 { 166 int max_count = sysctl_hung_task_check_count; 167 int batch_count = HUNG_TASK_BATCHING; 168 struct task_struct *g, *t; 169 170 /* 171 * If the system crashed already then all bets are off, 172 * do not report extra hung tasks: 173 */ 174 if (test_taint(TAINT_DIE) || did_panic) 175 return; 176 177 hung_task_show_lock = false; 178 rcu_read_lock(); 179 for_each_process_thread(g, t) { 180 if (!max_count--) 181 goto unlock; 182 if (!--batch_count) { 183 batch_count = HUNG_TASK_BATCHING; 184 if (!rcu_lock_break(g, t)) 185 goto unlock; 186 } 187 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */ 188 if (t->state == TASK_UNINTERRUPTIBLE) 189 check_hung_task(t, timeout); 190 } 191 unlock: 192 rcu_read_unlock(); 193 if (hung_task_show_lock) 194 debug_show_all_locks(); 195 if (hung_task_call_panic) { 196 trigger_all_cpu_backtrace(); 197 panic("hung_task: blocked tasks"); 198 } 199 } 200 201 static long hung_timeout_jiffies(unsigned long last_checked, 202 unsigned long timeout) 203 { 204 /* timeout of 0 will disable the watchdog */ 205 return timeout ? last_checked - jiffies + timeout * HZ : 206 MAX_SCHEDULE_TIMEOUT; 207 } 208 209 /* 210 * Process updating of timeout sysctl 211 */ 212 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write, 213 void __user *buffer, 214 size_t *lenp, loff_t *ppos) 215 { 216 int ret; 217 218 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); 219 220 if (ret || !write) 221 goto out; 222 223 wake_up_process(watchdog_task); 224 225 out: 226 return ret; 227 } 228 229 static atomic_t reset_hung_task = ATOMIC_INIT(0); 230 231 void reset_hung_task_detector(void) 232 { 233 atomic_set(&reset_hung_task, 1); 234 } 235 EXPORT_SYMBOL_GPL(reset_hung_task_detector); 236 237 /* 238 * kthread which checks for tasks stuck in D state 239 */ 240 static int watchdog(void *dummy) 241 { 242 unsigned long hung_last_checked = jiffies; 243 244 set_user_nice(current, 0); 245 246 for ( ; ; ) { 247 unsigned long timeout = sysctl_hung_task_timeout_secs; 248 long t = hung_timeout_jiffies(hung_last_checked, timeout); 249 250 if (t <= 0) { 251 if (!atomic_xchg(&reset_hung_task, 0)) 252 check_hung_uninterruptible_tasks(timeout); 253 hung_last_checked = jiffies; 254 continue; 255 } 256 schedule_timeout_interruptible(t); 257 } 258 259 return 0; 260 } 261 262 static int __init hung_task_init(void) 263 { 264 atomic_notifier_chain_register(&panic_notifier_list, &panic_block); 265 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd"); 266 267 return 0; 268 } 269 subsys_initcall(hung_task_init); 270