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 47 static struct task_struct *watchdog_task; 48 49 /* 50 * Should we panic (and reboot, if panic_timeout= is set) when a 51 * hung task is detected: 52 */ 53 unsigned int __read_mostly sysctl_hung_task_panic = 54 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE; 55 56 static int __init hung_task_panic_setup(char *str) 57 { 58 int rc = kstrtouint(str, 0, &sysctl_hung_task_panic); 59 60 if (rc) 61 return rc; 62 return 1; 63 } 64 __setup("hung_task_panic=", hung_task_panic_setup); 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 return; 100 } 101 102 trace_sched_process_hang(t); 103 104 if (!sysctl_hung_task_warnings && !sysctl_hung_task_panic) 105 return; 106 107 /* 108 * Ok, the task did not get scheduled for more than 2 minutes, 109 * complain: 110 */ 111 if (sysctl_hung_task_warnings) { 112 if (sysctl_hung_task_warnings > 0) 113 sysctl_hung_task_warnings--; 114 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n", 115 t->comm, t->pid, timeout); 116 pr_err(" %s %s %.*s\n", 117 print_tainted(), init_utsname()->release, 118 (int)strcspn(init_utsname()->version, " "), 119 init_utsname()->version); 120 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\"" 121 " disables this message.\n"); 122 sched_show_task(t); 123 debug_show_all_locks(); 124 } 125 126 touch_nmi_watchdog(); 127 128 if (sysctl_hung_task_panic) { 129 trigger_all_cpu_backtrace(); 130 panic("hung_task: blocked tasks"); 131 } 132 } 133 134 /* 135 * To avoid extending the RCU grace period for an unbounded amount of time, 136 * periodically exit the critical section and enter a new one. 137 * 138 * For preemptible RCU it is sufficient to call rcu_read_unlock in order 139 * to exit the grace period. For classic RCU, a reschedule is required. 140 */ 141 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t) 142 { 143 bool can_cont; 144 145 get_task_struct(g); 146 get_task_struct(t); 147 rcu_read_unlock(); 148 cond_resched(); 149 rcu_read_lock(); 150 can_cont = pid_alive(g) && pid_alive(t); 151 put_task_struct(t); 152 put_task_struct(g); 153 154 return can_cont; 155 } 156 157 /* 158 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for 159 * a really long time (120 seconds). If that happens, print out 160 * a warning. 161 */ 162 static void check_hung_uninterruptible_tasks(unsigned long timeout) 163 { 164 int max_count = sysctl_hung_task_check_count; 165 int batch_count = HUNG_TASK_BATCHING; 166 struct task_struct *g, *t; 167 168 /* 169 * If the system crashed already then all bets are off, 170 * do not report extra hung tasks: 171 */ 172 if (test_taint(TAINT_DIE) || did_panic) 173 return; 174 175 rcu_read_lock(); 176 for_each_process_thread(g, t) { 177 if (!max_count--) 178 goto unlock; 179 if (!--batch_count) { 180 batch_count = HUNG_TASK_BATCHING; 181 if (!rcu_lock_break(g, t)) 182 goto unlock; 183 } 184 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */ 185 if (t->state == TASK_UNINTERRUPTIBLE) 186 check_hung_task(t, timeout); 187 } 188 unlock: 189 rcu_read_unlock(); 190 } 191 192 static long hung_timeout_jiffies(unsigned long last_checked, 193 unsigned long timeout) 194 { 195 /* timeout of 0 will disable the watchdog */ 196 return timeout ? last_checked - jiffies + timeout * HZ : 197 MAX_SCHEDULE_TIMEOUT; 198 } 199 200 /* 201 * Process updating of timeout sysctl 202 */ 203 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write, 204 void __user *buffer, 205 size_t *lenp, loff_t *ppos) 206 { 207 int ret; 208 209 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); 210 211 if (ret || !write) 212 goto out; 213 214 wake_up_process(watchdog_task); 215 216 out: 217 return ret; 218 } 219 220 static atomic_t reset_hung_task = ATOMIC_INIT(0); 221 222 void reset_hung_task_detector(void) 223 { 224 atomic_set(&reset_hung_task, 1); 225 } 226 EXPORT_SYMBOL_GPL(reset_hung_task_detector); 227 228 /* 229 * kthread which checks for tasks stuck in D state 230 */ 231 static int watchdog(void *dummy) 232 { 233 unsigned long hung_last_checked = jiffies; 234 235 set_user_nice(current, 0); 236 237 for ( ; ; ) { 238 unsigned long timeout = sysctl_hung_task_timeout_secs; 239 long t = hung_timeout_jiffies(hung_last_checked, timeout); 240 241 if (t <= 0) { 242 if (!atomic_xchg(&reset_hung_task, 0)) 243 check_hung_uninterruptible_tasks(timeout); 244 hung_last_checked = jiffies; 245 continue; 246 } 247 schedule_timeout_interruptible(t); 248 } 249 250 return 0; 251 } 252 253 static int __init hung_task_init(void) 254 { 255 atomic_notifier_chain_register(&panic_notifier_list, &panic_block); 256 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd"); 257 258 return 0; 259 } 260 subsys_initcall(hung_task_init); 261