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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
48 static struct task_struct *watchdog_task;
49
50 /*
51  * Should we panic (and reboot, if panic_timeout= is set) when a
52  * hung task is detected:
53  */
54 unsigned int __read_mostly sysctl_hung_task_panic =
55                                 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
56
57 static int __init hung_task_panic_setup(char *str)
58 {
59         int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
60
61         if (rc)
62                 return rc;
63         return 1;
64 }
65 __setup("hung_task_panic=", hung_task_panic_setup);
66
67 static int
68 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
69 {
70         did_panic = 1;
71
72         return NOTIFY_DONE;
73 }
74
75 static struct notifier_block panic_block = {
76         .notifier_call = hung_task_panic,
77 };
78
79 static void check_hung_task(struct task_struct *t, unsigned long timeout)
80 {
81         unsigned long switch_count = t->nvcsw + t->nivcsw;
82
83         /*
84          * Ensure the task is not frozen.
85          * Also, skip vfork and any other user process that freezer should skip.
86          */
87         if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
88             return;
89
90         /*
91          * When a freshly created task is scheduled once, changes its state to
92          * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
93          * musn't be checked.
94          */
95         if (unlikely(!switch_count))
96                 return;
97
98         if (switch_count != t->last_switch_count) {
99                 t->last_switch_count = switch_count;
100                 return;
101         }
102
103         trace_sched_process_hang(t);
104
105         if (!sysctl_hung_task_warnings && !sysctl_hung_task_panic)
106                 return;
107
108         /*
109          * Ok, the task did not get scheduled for more than 2 minutes,
110          * complain:
111          */
112         if (sysctl_hung_task_warnings) {
113                 if (sysctl_hung_task_warnings > 0)
114                         sysctl_hung_task_warnings--;
115                 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
116                         t->comm, t->pid, timeout);
117                 pr_err("      %s %s %.*s\n",
118                         print_tainted(), init_utsname()->release,
119                         (int)strcspn(init_utsname()->version, " "),
120                         init_utsname()->version);
121                 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
122                         " disables this message.\n");
123                 sched_show_task(t);
124                 hung_task_show_lock = true;
125         }
126
127         touch_nmi_watchdog();
128
129         if (sysctl_hung_task_panic) {
130                 if (hung_task_show_lock)
131                         debug_show_all_locks();
132                 trigger_all_cpu_backtrace();
133                 panic("hung_task: blocked tasks");
134         }
135 }
136
137 /*
138  * To avoid extending the RCU grace period for an unbounded amount of time,
139  * periodically exit the critical section and enter a new one.
140  *
141  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
142  * to exit the grace period. For classic RCU, a reschedule is required.
143  */
144 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
145 {
146         bool can_cont;
147
148         get_task_struct(g);
149         get_task_struct(t);
150         rcu_read_unlock();
151         cond_resched();
152         rcu_read_lock();
153         can_cont = pid_alive(g) && pid_alive(t);
154         put_task_struct(t);
155         put_task_struct(g);
156
157         return can_cont;
158 }
159
160 /*
161  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
162  * a really long time (120 seconds). If that happens, print out
163  * a warning.
164  */
165 static void check_hung_uninterruptible_tasks(unsigned long timeout)
166 {
167         int max_count = sysctl_hung_task_check_count;
168         int batch_count = HUNG_TASK_BATCHING;
169         struct task_struct *g, *t;
170
171         /*
172          * If the system crashed already then all bets are off,
173          * do not report extra hung tasks:
174          */
175         if (test_taint(TAINT_DIE) || did_panic)
176                 return;
177
178         hung_task_show_lock = false;
179         rcu_read_lock();
180         for_each_process_thread(g, t) {
181                 if (!max_count--)
182                         goto unlock;
183                 if (!--batch_count) {
184                         batch_count = HUNG_TASK_BATCHING;
185                         if (!rcu_lock_break(g, t))
186                                 goto unlock;
187                 }
188                 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
189                 if (t->state == TASK_UNINTERRUPTIBLE)
190                         check_hung_task(t, timeout);
191         }
192  unlock:
193         rcu_read_unlock();
194         if (hung_task_show_lock)
195                 debug_show_all_locks();
196 }
197
198 static long hung_timeout_jiffies(unsigned long last_checked,
199                                  unsigned long timeout)
200 {
201         /* timeout of 0 will disable the watchdog */
202         return timeout ? last_checked - jiffies + timeout * HZ :
203                 MAX_SCHEDULE_TIMEOUT;
204 }
205
206 /*
207  * Process updating of timeout sysctl
208  */
209 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
210                                   void __user *buffer,
211                                   size_t *lenp, loff_t *ppos)
212 {
213         int ret;
214
215         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
216
217         if (ret || !write)
218                 goto out;
219
220         wake_up_process(watchdog_task);
221
222  out:
223         return ret;
224 }
225
226 static atomic_t reset_hung_task = ATOMIC_INIT(0);
227
228 void reset_hung_task_detector(void)
229 {
230         atomic_set(&reset_hung_task, 1);
231 }
232 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
233
234 /*
235  * kthread which checks for tasks stuck in D state
236  */
237 static int watchdog(void *dummy)
238 {
239         unsigned long hung_last_checked = jiffies;
240
241         set_user_nice(current, 0);
242
243         for ( ; ; ) {
244                 unsigned long timeout = sysctl_hung_task_timeout_secs;
245                 long t = hung_timeout_jiffies(hung_last_checked, timeout);
246
247                 if (t <= 0) {
248                         if (!atomic_xchg(&reset_hung_task, 0))
249                                 check_hung_uninterruptible_tasks(timeout);
250                         hung_last_checked = jiffies;
251                         continue;
252                 }
253                 schedule_timeout_interruptible(t);
254         }
255
256         return 0;
257 }
258
259 static int __init hung_task_init(void)
260 {
261         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
262         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
263
264         return 0;
265 }
266 subsys_initcall(hung_task_init);