1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Detect Hung Task
4 *
5 * kernel/hung_task.c - kernel thread for detecting tasks stuck in D state
6 *
7 */
8
9 #include <linux/mm.h>
10 #include <linux/cpu.h>
11 #include <linux/nmi.h>
12 #include <linux/init.h>
13 #include <linux/delay.h>
14 #include <linux/freezer.h>
15 #include <linux/kthread.h>
16 #include <linux/lockdep.h>
17 #include <linux/export.h>
18 #include <linux/panic_notifier.h>
19 #include <linux/sysctl.h>
20 #include <linux/suspend.h>
21 #include <linux/utsname.h>
22 #include <linux/sched/signal.h>
23 #include <linux/sched/debug.h>
24 #include <linux/sched/sysctl.h>
25
26 #include <trace/events/sched.h>
27
28 /*
29 * The number of tasks checked:
30 */
31 int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
32
33 /*
34 * Limit number of tasks checked in a batch.
35 *
36 * This value controls the preemptibility of khungtaskd since preemption
37 * is disabled during the critical section. It also controls the size of
38 * the RCU grace period. So it needs to be upper-bound.
39 */
40 #define HUNG_TASK_LOCK_BREAK (HZ / 10)
41
42 /*
43 * Zero means infinite timeout - no checking done:
44 */
45 unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
46
47 /*
48 * Zero (default value) means use sysctl_hung_task_timeout_secs:
49 */
50 unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
51
52 int __read_mostly sysctl_hung_task_warnings = 10;
53
54 static int __read_mostly did_panic;
55 static bool hung_task_show_lock;
56 static bool hung_task_call_panic;
57 static bool hung_task_show_all_bt;
58
59 static struct task_struct *watchdog_task;
60
61 #ifdef CONFIG_SMP
62 /*
63 * Should we dump all CPUs backtraces in a hung task event?
64 * Defaults to 0, can be changed via sysctl.
65 */
66 static unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace;
67 #else
68 #define sysctl_hung_task_all_cpu_backtrace 0
69 #endif /* CONFIG_SMP */
70
71 /*
72 * Should we panic (and reboot, if panic_timeout= is set) when a
73 * hung task is detected:
74 */
75 unsigned int __read_mostly sysctl_hung_task_panic =
76 IS_ENABLED(CONFIG_BOOTPARAM_HUNG_TASK_PANIC);
77
78 static int
hung_task_panic(struct notifier_block * this,unsigned long event,void * ptr)79 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
80 {
81 did_panic = 1;
82
83 return NOTIFY_DONE;
84 }
85
86 static struct notifier_block panic_block = {
87 .notifier_call = hung_task_panic,
88 };
89
check_hung_task(struct task_struct * t,unsigned long timeout)90 static void check_hung_task(struct task_struct *t, unsigned long timeout)
91 {
92 unsigned long switch_count = t->nvcsw + t->nivcsw;
93
94 /*
95 * Ensure the task is not frozen.
96 * Also, skip vfork and any other user process that freezer should skip.
97 */
98 if (unlikely(READ_ONCE(t->__state) & TASK_FROZEN))
99 return;
100
101 /*
102 * When a freshly created task is scheduled once, changes its state to
103 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
104 * musn't be checked.
105 */
106 if (unlikely(!switch_count))
107 return;
108
109 if (switch_count != t->last_switch_count) {
110 t->last_switch_count = switch_count;
111 t->last_switch_time = jiffies;
112 return;
113 }
114 if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
115 return;
116
117 trace_sched_process_hang(t);
118
119 if (sysctl_hung_task_panic) {
120 console_verbose();
121 hung_task_show_lock = true;
122 hung_task_call_panic = true;
123 }
124
125 /*
126 * Ok, the task did not get scheduled for more than 2 minutes,
127 * complain:
128 */
129 if (sysctl_hung_task_warnings) {
130 if (sysctl_hung_task_warnings > 0)
131 sysctl_hung_task_warnings--;
132 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
133 t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
134 pr_err(" %s %s %.*s\n",
135 print_tainted(), init_utsname()->release,
136 (int)strcspn(init_utsname()->version, " "),
137 init_utsname()->version);
138 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
139 " disables this message.\n");
140 sched_show_task(t);
141 hung_task_show_lock = true;
142
143 if (sysctl_hung_task_all_cpu_backtrace)
144 hung_task_show_all_bt = true;
145 }
146
147 touch_nmi_watchdog();
148 }
149
150 /*
151 * To avoid extending the RCU grace period for an unbounded amount of time,
152 * periodically exit the critical section and enter a new one.
153 *
154 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
155 * to exit the grace period. For classic RCU, a reschedule is required.
156 */
rcu_lock_break(struct task_struct * g,struct task_struct * t)157 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
158 {
159 bool can_cont;
160
161 get_task_struct(g);
162 get_task_struct(t);
163 rcu_read_unlock();
164 cond_resched();
165 rcu_read_lock();
166 can_cont = pid_alive(g) && pid_alive(t);
167 put_task_struct(t);
168 put_task_struct(g);
169
170 return can_cont;
171 }
172
173 /*
174 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
175 * a really long time (120 seconds). If that happens, print out
176 * a warning.
177 */
check_hung_uninterruptible_tasks(unsigned long timeout)178 static void check_hung_uninterruptible_tasks(unsigned long timeout)
179 {
180 int max_count = sysctl_hung_task_check_count;
181 unsigned long last_break = jiffies;
182 struct task_struct *g, *t;
183
184 /*
185 * If the system crashed already then all bets are off,
186 * do not report extra hung tasks:
187 */
188 if (test_taint(TAINT_DIE) || did_panic)
189 return;
190
191 hung_task_show_lock = false;
192 rcu_read_lock();
193 for_each_process_thread(g, t) {
194 unsigned int state;
195
196 if (!max_count--)
197 goto unlock;
198 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
199 if (!rcu_lock_break(g, t))
200 goto unlock;
201 last_break = jiffies;
202 }
203 /*
204 * skip the TASK_KILLABLE tasks -- these can be killed
205 * skip the TASK_IDLE tasks -- those are genuinely idle
206 */
207 state = READ_ONCE(t->__state);
208 if ((state & TASK_UNINTERRUPTIBLE) &&
209 !(state & TASK_WAKEKILL) &&
210 !(state & TASK_NOLOAD))
211 check_hung_task(t, timeout);
212 }
213 unlock:
214 rcu_read_unlock();
215 if (hung_task_show_lock)
216 debug_show_all_locks();
217
218 if (hung_task_show_all_bt) {
219 hung_task_show_all_bt = false;
220 trigger_all_cpu_backtrace();
221 }
222
223 if (hung_task_call_panic)
224 panic("hung_task: blocked tasks");
225 }
226
hung_timeout_jiffies(unsigned long last_checked,unsigned long timeout)227 static long hung_timeout_jiffies(unsigned long last_checked,
228 unsigned long timeout)
229 {
230 /* timeout of 0 will disable the watchdog */
231 return timeout ? last_checked - jiffies + timeout * HZ :
232 MAX_SCHEDULE_TIMEOUT;
233 }
234
235 #ifdef CONFIG_SYSCTL
236 /*
237 * Process updating of timeout sysctl
238 */
proc_dohung_task_timeout_secs(struct ctl_table * table,int write,void * buffer,size_t * lenp,loff_t * ppos)239 static int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
240 void *buffer,
241 size_t *lenp, loff_t *ppos)
242 {
243 int ret;
244
245 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
246
247 if (ret || !write)
248 goto out;
249
250 wake_up_process(watchdog_task);
251
252 out:
253 return ret;
254 }
255
256 /*
257 * This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs
258 * and hung_task_check_interval_secs
259 */
260 static const unsigned long hung_task_timeout_max = (LONG_MAX / HZ);
261 static struct ctl_table hung_task_sysctls[] = {
262 #ifdef CONFIG_SMP
263 {
264 .procname = "hung_task_all_cpu_backtrace",
265 .data = &sysctl_hung_task_all_cpu_backtrace,
266 .maxlen = sizeof(int),
267 .mode = 0644,
268 .proc_handler = proc_dointvec_minmax,
269 .extra1 = SYSCTL_ZERO,
270 .extra2 = SYSCTL_ONE,
271 },
272 #endif /* CONFIG_SMP */
273 {
274 .procname = "hung_task_panic",
275 .data = &sysctl_hung_task_panic,
276 .maxlen = sizeof(int),
277 .mode = 0644,
278 .proc_handler = proc_dointvec_minmax,
279 .extra1 = SYSCTL_ZERO,
280 .extra2 = SYSCTL_ONE,
281 },
282 {
283 .procname = "hung_task_check_count",
284 .data = &sysctl_hung_task_check_count,
285 .maxlen = sizeof(int),
286 .mode = 0644,
287 .proc_handler = proc_dointvec_minmax,
288 .extra1 = SYSCTL_ZERO,
289 },
290 {
291 .procname = "hung_task_timeout_secs",
292 .data = &sysctl_hung_task_timeout_secs,
293 .maxlen = sizeof(unsigned long),
294 .mode = 0644,
295 .proc_handler = proc_dohung_task_timeout_secs,
296 .extra2 = (void *)&hung_task_timeout_max,
297 },
298 {
299 .procname = "hung_task_check_interval_secs",
300 .data = &sysctl_hung_task_check_interval_secs,
301 .maxlen = sizeof(unsigned long),
302 .mode = 0644,
303 .proc_handler = proc_dohung_task_timeout_secs,
304 .extra2 = (void *)&hung_task_timeout_max,
305 },
306 {
307 .procname = "hung_task_warnings",
308 .data = &sysctl_hung_task_warnings,
309 .maxlen = sizeof(int),
310 .mode = 0644,
311 .proc_handler = proc_dointvec_minmax,
312 .extra1 = SYSCTL_NEG_ONE,
313 },
314 {}
315 };
316
hung_task_sysctl_init(void)317 static void __init hung_task_sysctl_init(void)
318 {
319 register_sysctl_init("kernel", hung_task_sysctls);
320 }
321 #else
322 #define hung_task_sysctl_init() do { } while (0)
323 #endif /* CONFIG_SYSCTL */
324
325
326 static atomic_t reset_hung_task = ATOMIC_INIT(0);
327
reset_hung_task_detector(void)328 void reset_hung_task_detector(void)
329 {
330 atomic_set(&reset_hung_task, 1);
331 }
332 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
333
334 static bool hung_detector_suspended;
335
hungtask_pm_notify(struct notifier_block * self,unsigned long action,void * hcpu)336 static int hungtask_pm_notify(struct notifier_block *self,
337 unsigned long action, void *hcpu)
338 {
339 switch (action) {
340 case PM_SUSPEND_PREPARE:
341 case PM_HIBERNATION_PREPARE:
342 case PM_RESTORE_PREPARE:
343 hung_detector_suspended = true;
344 break;
345 case PM_POST_SUSPEND:
346 case PM_POST_HIBERNATION:
347 case PM_POST_RESTORE:
348 hung_detector_suspended = false;
349 break;
350 default:
351 break;
352 }
353 return NOTIFY_OK;
354 }
355
356 /*
357 * kthread which checks for tasks stuck in D state
358 */
watchdog(void * dummy)359 static int watchdog(void *dummy)
360 {
361 unsigned long hung_last_checked = jiffies;
362
363 set_user_nice(current, 0);
364
365 for ( ; ; ) {
366 unsigned long timeout = sysctl_hung_task_timeout_secs;
367 unsigned long interval = sysctl_hung_task_check_interval_secs;
368 long t;
369
370 if (interval == 0)
371 interval = timeout;
372 interval = min_t(unsigned long, interval, timeout);
373 t = hung_timeout_jiffies(hung_last_checked, interval);
374 if (t <= 0) {
375 if (!atomic_xchg(&reset_hung_task, 0) &&
376 !hung_detector_suspended)
377 check_hung_uninterruptible_tasks(timeout);
378 hung_last_checked = jiffies;
379 continue;
380 }
381 schedule_timeout_interruptible(t);
382 }
383
384 return 0;
385 }
386
hung_task_init(void)387 static int __init hung_task_init(void)
388 {
389 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
390
391 /* Disable hung task detector on suspend */
392 pm_notifier(hungtask_pm_notify, 0);
393
394 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
395 hung_task_sysctl_init();
396
397 return 0;
398 }
399 subsys_initcall(hung_task_init);
400
