Line data Source code
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 <trace/events/sched.h>
20 :
21 : /*
22 : * The number of tasks checked:
23 : */
24 : int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
25 :
26 : /*
27 : * Limit number of tasks checked in a batch.
28 : *
29 : * This value controls the preemptibility of khungtaskd since preemption
30 : * is disabled during the critical section. It also controls the size of
31 : * the RCU grace period. So it needs to be upper-bound.
32 : */
33 : #define HUNG_TASK_BATCHING 1024
34 :
35 : /*
36 : * Zero means infinite timeout - no checking done:
37 : */
38 : unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
39 :
40 : int __read_mostly sysctl_hung_task_warnings = 10;
41 :
42 : static int __read_mostly did_panic;
43 :
44 : static struct task_struct *watchdog_task;
45 :
46 : /*
47 : * Should we panic (and reboot, if panic_timeout= is set) when a
48 : * hung task is detected:
49 : */
50 : unsigned int __read_mostly sysctl_hung_task_panic =
51 : CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
52 :
53 0 : static int __init hung_task_panic_setup(char *str)
54 : {
55 0 : int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
56 :
57 0 : if (rc)
58 0 : return rc;
59 : return 1;
60 : }
61 : __setup("hung_task_panic=", hung_task_panic_setup);
62 :
63 : static int
64 0 : hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
65 : {
66 0 : did_panic = 1;
67 :
68 0 : return NOTIFY_DONE;
69 : }
70 :
71 : static struct notifier_block panic_block = {
72 : .notifier_call = hung_task_panic,
73 : };
74 :
75 1 : static void check_hung_task(struct task_struct *t, unsigned long timeout)
76 : {
77 1 : unsigned long switch_count = t->nvcsw + t->nivcsw;
78 :
79 : /*
80 : * Ensure the task is not frozen.
81 : * Also, skip vfork and any other user process that freezer should skip.
82 : */
83 1 : if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
84 : return;
85 :
86 : /*
87 : * When a freshly created task is scheduled once, changes its state to
88 : * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
89 : * musn't be checked.
90 : */
91 1 : if (unlikely(!switch_count))
92 : return;
93 :
94 1 : if (switch_count != t->last_switch_count) {
95 1 : t->last_switch_count = switch_count;
96 1 : return;
97 : }
98 :
99 : trace_sched_process_hang(t);
100 :
101 0 : if (!sysctl_hung_task_warnings)
102 : return;
103 :
104 0 : if (sysctl_hung_task_warnings > 0)
105 0 : sysctl_hung_task_warnings--;
106 :
107 : /*
108 : * Ok, the task did not get scheduled for more than 2 minutes,
109 : * complain:
110 : */
111 0 : pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
112 : t->comm, t->pid, timeout);
113 0 : pr_err(" %s %s %.*s\n",
114 : print_tainted(), init_utsname()->release,
115 : (int)strcspn(init_utsname()->version, " "),
116 : init_utsname()->version);
117 0 : pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
118 : " disables this message.\n");
119 0 : sched_show_task(t);
120 : debug_show_held_locks(t);
121 :
122 : touch_nmi_watchdog();
123 :
124 0 : if (sysctl_hung_task_panic) {
125 : trigger_all_cpu_backtrace();
126 0 : panic("hung_task: blocked tasks");
127 : }
128 : }
129 :
130 : /*
131 : * To avoid extending the RCU grace period for an unbounded amount of time,
132 : * periodically exit the critical section and enter a new one.
133 : *
134 : * For preemptible RCU it is sufficient to call rcu_read_unlock in order
135 : * to exit the grace period. For classic RCU, a reschedule is required.
136 : */
137 0 : static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
138 : {
139 : bool can_cont;
140 :
141 0 : get_task_struct(g);
142 0 : get_task_struct(t);
143 : rcu_read_unlock();
144 0 : cond_resched();
145 : rcu_read_lock();
146 0 : can_cont = pid_alive(g) && pid_alive(t);
147 : put_task_struct(t);
148 : put_task_struct(g);
149 :
150 0 : return can_cont;
151 : }
152 :
153 : /*
154 : * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
155 : * a really long time (120 seconds). If that happens, print out
156 : * a warning.
157 : */
158 21 : static void check_hung_uninterruptible_tasks(unsigned long timeout)
159 : {
160 21 : int max_count = sysctl_hung_task_check_count;
161 : int batch_count = HUNG_TASK_BATCHING;
162 : struct task_struct *g, *t;
163 :
164 : /*
165 : * If the system crashed already then all bets are off,
166 : * do not report extra hung tasks:
167 : */
168 21 : if (test_taint(TAINT_DIE) || did_panic)
169 21 : return;
170 :
171 : rcu_read_lock();
172 1491 : do_each_thread(g, t) {
173 1575 : if (!max_count--)
174 : goto unlock;
175 1575 : if (!--batch_count) {
176 : batch_count = HUNG_TASK_BATCHING;
177 0 : if (!rcu_lock_break(g, t))
178 : goto unlock;
179 : }
180 : /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
181 1575 : if (t->state == TASK_UNINTERRUPTIBLE)
182 1 : check_hung_task(t, timeout);
183 1575 : } while_each_thread(g, t);
184 : unlock:
185 : rcu_read_unlock();
186 : }
187 :
188 : static unsigned long timeout_jiffies(unsigned long timeout)
189 : {
190 : /* timeout of 0 will disable the watchdog */
191 22 : return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT;
192 : }
193 :
194 : /*
195 : * Process updating of timeout sysctl
196 : */
197 0 : int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
198 : void __user *buffer,
199 : size_t *lenp, loff_t *ppos)
200 : {
201 : int ret;
202 :
203 0 : ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
204 :
205 0 : if (ret || !write)
206 : goto out;
207 :
208 0 : wake_up_process(watchdog_task);
209 :
210 : out:
211 0 : return ret;
212 : }
213 :
214 : static atomic_t reset_hung_task = ATOMIC_INIT(0);
215 :
216 0 : void reset_hung_task_detector(void)
217 : {
218 0 : atomic_set(&reset_hung_task, 1);
219 0 : }
220 : EXPORT_SYMBOL_GPL(reset_hung_task_detector);
221 :
222 : /*
223 : * kthread which checks for tasks stuck in D state
224 : */
225 1 : static int watchdog(void *dummy)
226 : {
227 1 : set_user_nice(current, 0);
228 :
229 : for ( ; ; ) {
230 22 : unsigned long timeout = sysctl_hung_task_timeout_secs;
231 :
232 44 : while (schedule_timeout_interruptible(timeout_jiffies(timeout)))
233 0 : timeout = sysctl_hung_task_timeout_secs;
234 :
235 21 : if (atomic_xchg(&reset_hung_task, 0))
236 0 : continue;
237 :
238 21 : check_hung_uninterruptible_tasks(timeout);
239 : }
240 :
241 : return 0;
242 : }
243 :
244 1 : static int __init hung_task_init(void)
245 : {
246 1 : atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
247 2 : watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
248 :
249 1 : return 0;
250 : }
251 : subsys_initcall(hung_task_init);
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