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 #include <trace/hooks/hung_task.h>
28
29 /*
30 * The number of tasks checked:
31 */
32 static int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
33
34 /*
35 * Limit number of tasks checked in a batch.
36 *
37 * This value controls the preemptibility of khungtaskd since preemption
38 * is disabled during the critical section. It also controls the size of
39 * the RCU grace period. So it needs to be upper-bound.
40 */
41 #define HUNG_TASK_LOCK_BREAK (HZ / 10)
42
43 /*
44 * Zero means infinite timeout - no checking done:
45 */
46 unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
47
48 /*
49 * Zero (default value) means use sysctl_hung_task_timeout_secs:
50 */
51 static unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
52
53 static int __read_mostly sysctl_hung_task_warnings = 10;
54
55 static int __read_mostly did_panic;
56 static bool hung_task_show_lock;
57 static bool hung_task_call_panic;
58 static bool hung_task_show_all_bt;
59
60 static struct task_struct *watchdog_task;
61
62 #ifdef CONFIG_SMP
63 /*
64 * Should we dump all CPUs backtraces in a hung task event?
65 * Defaults to 0, can be changed via sysctl.
66 */
67 static unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace;
68 #else
69 #define sysctl_hung_task_all_cpu_backtrace 0
70 #endif /* CONFIG_SMP */
71
72 /*
73 * Should we panic (and reboot, if panic_timeout= is set) when a
74 * hung task is detected:
75 */
76 static unsigned int __read_mostly sysctl_hung_task_panic =
77 IS_ENABLED(CONFIG_BOOTPARAM_HUNG_TASK_PANIC);
78
79 static int
hung_task_panic(struct notifier_block * this,unsigned long event,void * ptr)80 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
81 {
82 did_panic = 1;
83
84 return NOTIFY_DONE;
85 }
86
87 static struct notifier_block panic_block = {
88 .notifier_call = hung_task_panic,
89 };
90
check_hung_task(struct task_struct * t,unsigned long timeout)91 static void check_hung_task(struct task_struct *t, unsigned long timeout)
92 {
93 unsigned long switch_count = t->nvcsw + t->nivcsw;
94
95 /*
96 * Ensure the task is not frozen.
97 * Also, skip vfork and any other user process that freezer should skip.
98 */
99 if (unlikely(READ_ONCE(t->__state) & TASK_FROZEN))
100 return;
101
102 /*
103 * When a freshly created task is scheduled once, changes its state to
104 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
105 * musn't be checked.
106 */
107 if (unlikely(!switch_count))
108 return;
109
110 if (switch_count != t->last_switch_count) {
111 t->last_switch_count = switch_count;
112 t->last_switch_time = jiffies;
113 return;
114 }
115 if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
116 return;
117
118 trace_sched_process_hang(t);
119
120 if (sysctl_hung_task_panic) {
121 console_verbose();
122 hung_task_show_lock = true;
123 hung_task_call_panic = true;
124 }
125
126 /*
127 * Ok, the task did not get scheduled for more than 2 minutes,
128 * complain:
129 */
130 if (sysctl_hung_task_warnings) {
131 if (sysctl_hung_task_warnings > 0)
132 sysctl_hung_task_warnings--;
133 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
134 t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
135 pr_err(" %s %s %.*s\n",
136 print_tainted(), init_utsname()->release,
137 (int)strcspn(init_utsname()->version, " "),
138 init_utsname()->version);
139 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
140 " disables this message.\n");
141 sched_show_task(t);
142 hung_task_show_lock = true;
143
144 if (sysctl_hung_task_all_cpu_backtrace)
145 hung_task_show_all_bt = true;
146 if (!sysctl_hung_task_warnings)
147 pr_info("Future hung task reports are suppressed, see sysctl kernel.hung_task_warnings\n");
148 }
149
150 touch_nmi_watchdog();
151 }
152
153 /*
154 * To avoid extending the RCU grace period for an unbounded amount of time,
155 * periodically exit the critical section and enter a new one.
156 *
157 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
158 * to exit the grace period. For classic RCU, a reschedule is required.
159 */
rcu_lock_break(struct task_struct * g,struct task_struct * t)160 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
161 {
162 bool can_cont;
163
164 get_task_struct(g);
165 get_task_struct(t);
166 rcu_read_unlock();
167 cond_resched();
168 rcu_read_lock();
169 can_cont = pid_alive(g) && pid_alive(t);
170 put_task_struct(t);
171 put_task_struct(g);
172
173 return can_cont;
174 }
175
176 /*
177 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
178 * a really long time (120 seconds). If that happens, print out
179 * a warning.
180 */
check_hung_uninterruptible_tasks(unsigned long timeout)181 static void check_hung_uninterruptible_tasks(unsigned long timeout)
182 {
183 int max_count = sysctl_hung_task_check_count;
184 unsigned long last_break = jiffies;
185 struct task_struct *g, *t;
186 bool need_check = true;
187
188 /*
189 * If the system crashed already then all bets are off,
190 * do not report extra hung tasks:
191 */
192 if (test_taint(TAINT_DIE) || did_panic)
193 return;
194
195 hung_task_show_lock = false;
196 rcu_read_lock();
197 for_each_process_thread(g, t) {
198 unsigned int state;
199
200 if (!max_count--)
201 goto unlock;
202 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
203 if (!rcu_lock_break(g, t))
204 goto unlock;
205 last_break = jiffies;
206 }
207 /*
208 * skip the TASK_KILLABLE tasks -- these can be killed
209 * skip the TASK_IDLE tasks -- those are genuinely idle
210 */
211 trace_android_vh_check_uninterruptible_tasks(t, timeout, &need_check);
212 if (need_check) {
213 state = READ_ONCE(t->__state);
214 if ((state & TASK_UNINTERRUPTIBLE) &&
215 !(state & TASK_WAKEKILL) &&
216 !(state & TASK_NOLOAD))
217 check_hung_task(t, timeout);
218 }
219 }
220 trace_android_vh_check_uninterruptible_tasks_dn(NULL);
221 unlock:
222 rcu_read_unlock();
223 if (hung_task_show_lock)
224 debug_show_all_locks();
225
226 if (hung_task_show_all_bt) {
227 hung_task_show_all_bt = false;
228 trigger_all_cpu_backtrace();
229 }
230
231 if (hung_task_call_panic)
232 panic("hung_task: blocked tasks");
233 }
234
hung_timeout_jiffies(unsigned long last_checked,unsigned long timeout)235 static long hung_timeout_jiffies(unsigned long last_checked,
236 unsigned long timeout)
237 {
238 /* timeout of 0 will disable the watchdog */
239 return timeout ? last_checked - jiffies + timeout * HZ :
240 MAX_SCHEDULE_TIMEOUT;
241 }
242
243 #ifdef CONFIG_SYSCTL
244 /*
245 * Process updating of timeout sysctl
246 */
proc_dohung_task_timeout_secs(struct ctl_table * table,int write,void * buffer,size_t * lenp,loff_t * ppos)247 static int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
248 void *buffer,
249 size_t *lenp, loff_t *ppos)
250 {
251 int ret;
252
253 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
254
255 if (ret || !write)
256 goto out;
257
258 wake_up_process(watchdog_task);
259
260 out:
261 return ret;
262 }
263
264 /*
265 * This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs
266 * and hung_task_check_interval_secs
267 */
268 static const unsigned long hung_task_timeout_max = (LONG_MAX / HZ);
269 static struct ctl_table hung_task_sysctls[] = {
270 #ifdef CONFIG_SMP
271 {
272 .procname = "hung_task_all_cpu_backtrace",
273 .data = &sysctl_hung_task_all_cpu_backtrace,
274 .maxlen = sizeof(int),
275 .mode = 0644,
276 .proc_handler = proc_dointvec_minmax,
277 .extra1 = SYSCTL_ZERO,
278 .extra2 = SYSCTL_ONE,
279 },
280 #endif /* CONFIG_SMP */
281 {
282 .procname = "hung_task_panic",
283 .data = &sysctl_hung_task_panic,
284 .maxlen = sizeof(int),
285 .mode = 0644,
286 .proc_handler = proc_dointvec_minmax,
287 .extra1 = SYSCTL_ZERO,
288 .extra2 = SYSCTL_ONE,
289 },
290 {
291 .procname = "hung_task_check_count",
292 .data = &sysctl_hung_task_check_count,
293 .maxlen = sizeof(int),
294 .mode = 0644,
295 .proc_handler = proc_dointvec_minmax,
296 .extra1 = SYSCTL_ZERO,
297 },
298 {
299 .procname = "hung_task_timeout_secs",
300 .data = &sysctl_hung_task_timeout_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_check_interval_secs",
308 .data = &sysctl_hung_task_check_interval_secs,
309 .maxlen = sizeof(unsigned long),
310 .mode = 0644,
311 .proc_handler = proc_dohung_task_timeout_secs,
312 .extra2 = (void *)&hung_task_timeout_max,
313 },
314 {
315 .procname = "hung_task_warnings",
316 .data = &sysctl_hung_task_warnings,
317 .maxlen = sizeof(int),
318 .mode = 0644,
319 .proc_handler = proc_dointvec_minmax,
320 .extra1 = SYSCTL_NEG_ONE,
321 },
322 {}
323 };
324
hung_task_sysctl_init(void)325 static void __init hung_task_sysctl_init(void)
326 {
327 register_sysctl_init("kernel", hung_task_sysctls);
328 }
329 #else
330 #define hung_task_sysctl_init() do { } while (0)
331 #endif /* CONFIG_SYSCTL */
332
333
334 static atomic_t reset_hung_task = ATOMIC_INIT(0);
335
reset_hung_task_detector(void)336 void reset_hung_task_detector(void)
337 {
338 atomic_set(&reset_hung_task, 1);
339 }
340 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
341
342 static bool hung_detector_suspended;
343
hungtask_pm_notify(struct notifier_block * self,unsigned long action,void * hcpu)344 static int hungtask_pm_notify(struct notifier_block *self,
345 unsigned long action, void *hcpu)
346 {
347 switch (action) {
348 case PM_SUSPEND_PREPARE:
349 case PM_HIBERNATION_PREPARE:
350 case PM_RESTORE_PREPARE:
351 hung_detector_suspended = true;
352 break;
353 case PM_POST_SUSPEND:
354 case PM_POST_HIBERNATION:
355 case PM_POST_RESTORE:
356 hung_detector_suspended = false;
357 break;
358 default:
359 break;
360 }
361 return NOTIFY_OK;
362 }
363
364 /*
365 * kthread which checks for tasks stuck in D state
366 */
watchdog(void * dummy)367 static int watchdog(void *dummy)
368 {
369 unsigned long hung_last_checked = jiffies;
370
371 set_user_nice(current, 0);
372
373 for ( ; ; ) {
374 unsigned long timeout = sysctl_hung_task_timeout_secs;
375 unsigned long interval = sysctl_hung_task_check_interval_secs;
376 long t;
377
378 if (interval == 0)
379 interval = timeout;
380 interval = min_t(unsigned long, interval, timeout);
381 t = hung_timeout_jiffies(hung_last_checked, interval);
382 if (t <= 0) {
383 if (!atomic_xchg(&reset_hung_task, 0) &&
384 !hung_detector_suspended)
385 check_hung_uninterruptible_tasks(timeout);
386 hung_last_checked = jiffies;
387 continue;
388 }
389 schedule_timeout_interruptible(t);
390 }
391
392 return 0;
393 }
394
hung_task_init(void)395 static int __init hung_task_init(void)
396 {
397 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
398
399 /* Disable hung task detector on suspend */
400 pm_notifier(hungtask_pm_notify, 0);
401
402 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
403 hung_task_sysctl_init();
404
405 return 0;
406 }
407 subsys_initcall(hung_task_init);
408