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 /*
44 * Zero (default value) means use sysctl_hung_task_timeout_secs:
45 */
46 unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
47
48 int __read_mostly sysctl_hung_task_warnings = 10;
49
50 static int __read_mostly did_panic;
51 static bool hung_task_show_lock;
52 static bool hung_task_call_panic;
53
54 static struct task_struct *watchdog_task;
55
56 /*
57 * Should we panic (and reboot, if panic_timeout= is set) when a
58 * hung task is detected:
59 */
60 unsigned int __read_mostly sysctl_hung_task_panic =
61 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
62
hung_task_panic_setup(char * str)63 static int __init hung_task_panic_setup(char *str)
64 {
65 int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
66
67 if (rc)
68 return rc;
69 return 1;
70 }
71 __setup("hung_task_panic=", hung_task_panic_setup);
72
73 static int
hung_task_panic(struct notifier_block * this,unsigned long event,void * ptr)74 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
75 {
76 did_panic = 1;
77
78 return NOTIFY_DONE;
79 }
80
81 static struct notifier_block panic_block = {
82 .notifier_call = hung_task_panic,
83 };
84
check_hung_task(struct task_struct * t,unsigned long timeout)85 static void check_hung_task(struct task_struct *t, unsigned long timeout)
86 {
87 unsigned long switch_count = t->nvcsw + t->nivcsw;
88
89 /*
90 * Ensure the task is not frozen.
91 * Also, skip vfork and any other user process that freezer should skip.
92 */
93 if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
94 return;
95
96 /*
97 * When a freshly created task is scheduled once, changes its state to
98 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
99 * musn't be checked.
100 */
101 if (unlikely(!switch_count))
102 return;
103
104 if (switch_count != t->last_switch_count) {
105 t->last_switch_count = switch_count;
106 t->last_switch_time = jiffies;
107 return;
108 }
109 if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
110 return;
111
112 trace_sched_process_hang(t);
113
114 if (!sysctl_hung_task_warnings && !sysctl_hung_task_panic)
115 return;
116
117 /*
118 * Ok, the task did not get scheduled for more than 2 minutes,
119 * complain:
120 */
121 if (sysctl_hung_task_warnings) {
122 if (sysctl_hung_task_warnings > 0)
123 sysctl_hung_task_warnings--;
124 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
125 t->comm, t->pid, timeout);
126 pr_err(" %s %s %.*s\n",
127 print_tainted(), init_utsname()->release,
128 (int)strcspn(init_utsname()->version, " "),
129 init_utsname()->version);
130 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
131 " disables this message.\n");
132 sched_show_task(t);
133 hung_task_show_lock = true;
134 }
135
136 touch_nmi_watchdog();
137
138 if (sysctl_hung_task_panic) {
139 hung_task_show_lock = true;
140 hung_task_call_panic = true;
141 }
142 }
143
144 /*
145 * To avoid extending the RCU grace period for an unbounded amount of time,
146 * periodically exit the critical section and enter a new one.
147 *
148 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
149 * to exit the grace period. For classic RCU, a reschedule is required.
150 */
rcu_lock_break(struct task_struct * g,struct task_struct * t)151 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
152 {
153 bool can_cont;
154
155 get_task_struct(g);
156 get_task_struct(t);
157 rcu_read_unlock();
158 cond_resched();
159 rcu_read_lock();
160 can_cont = pid_alive(g) && pid_alive(t);
161 put_task_struct(t);
162 put_task_struct(g);
163
164 return can_cont;
165 }
166
167 /*
168 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
169 * a really long time (120 seconds). If that happens, print out
170 * a warning.
171 */
check_hung_uninterruptible_tasks(unsigned long timeout)172 static void check_hung_uninterruptible_tasks(unsigned long timeout)
173 {
174 int max_count = sysctl_hung_task_check_count;
175 int batch_count = HUNG_TASK_BATCHING;
176 struct task_struct *g, *t;
177
178 /*
179 * If the system crashed already then all bets are off,
180 * do not report extra hung tasks:
181 */
182 if (test_taint(TAINT_DIE) || did_panic)
183 return;
184
185 hung_task_show_lock = false;
186 rcu_read_lock();
187 for_each_process_thread(g, t) {
188 if (!max_count--)
189 goto unlock;
190 if (!--batch_count) {
191 batch_count = HUNG_TASK_BATCHING;
192 if (!rcu_lock_break(g, t))
193 goto unlock;
194 }
195 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
196 if (t->state == TASK_UNINTERRUPTIBLE)
197 check_hung_task(t, timeout);
198 }
199 unlock:
200 rcu_read_unlock();
201 if (hung_task_show_lock)
202 debug_show_all_locks();
203 if (hung_task_call_panic) {
204 trigger_all_cpu_backtrace();
205 panic("hung_task: blocked tasks");
206 }
207 }
208
hung_timeout_jiffies(unsigned long last_checked,unsigned long timeout)209 static long hung_timeout_jiffies(unsigned long last_checked,
210 unsigned long timeout)
211 {
212 /* timeout of 0 will disable the watchdog */
213 return timeout ? last_checked - jiffies + timeout * HZ :
214 MAX_SCHEDULE_TIMEOUT;
215 }
216
217 /*
218 * Process updating of timeout sysctl
219 */
proc_dohung_task_timeout_secs(struct ctl_table * table,int write,void __user * buffer,size_t * lenp,loff_t * ppos)220 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
221 void __user *buffer,
222 size_t *lenp, loff_t *ppos)
223 {
224 int ret;
225
226 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
227
228 if (ret || !write)
229 goto out;
230
231 wake_up_process(watchdog_task);
232
233 out:
234 return ret;
235 }
236
237 static atomic_t reset_hung_task = ATOMIC_INIT(0);
238
reset_hung_task_detector(void)239 void reset_hung_task_detector(void)
240 {
241 atomic_set(&reset_hung_task, 1);
242 }
243 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
244
245 /*
246 * kthread which checks for tasks stuck in D state
247 */
watchdog(void * dummy)248 static int watchdog(void *dummy)
249 {
250 unsigned long hung_last_checked = jiffies;
251
252 set_user_nice(current, 0);
253
254 for ( ; ; ) {
255 unsigned long timeout = sysctl_hung_task_timeout_secs;
256 unsigned long interval = sysctl_hung_task_check_interval_secs;
257 long t;
258
259 if (interval == 0)
260 interval = timeout;
261 interval = min_t(unsigned long, interval, timeout);
262 t = hung_timeout_jiffies(hung_last_checked, interval);
263 if (t <= 0) {
264 if (!atomic_xchg(&reset_hung_task, 0))
265 check_hung_uninterruptible_tasks(timeout);
266 hung_last_checked = jiffies;
267 continue;
268 }
269 schedule_timeout_interruptible(t);
270 }
271
272 return 0;
273 }
274
hung_task_init(void)275 static int __init hung_task_init(void)
276 {
277 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
278 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
279
280 return 0;
281 }
282 subsys_initcall(hung_task_init);
283
