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 | static 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 | static unsigned long __read_mostly sysctl_hung_task_check_interval_secs; |
51 | |
52 | static 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 | static unsigned int __read_mostly sysctl_hung_task_panic = |
76 | IS_ENABLED(CONFIG_BOOTPARAM_HUNG_TASK_PANIC); |
77 | |
78 | static int |
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 | |
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(tsk: 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(p: t); |
141 | hung_task_show_lock = true; |
142 | |
143 | if (sysctl_hung_task_all_cpu_backtrace) |
144 | hung_task_show_all_bt = true; |
145 | if (!sysctl_hung_task_warnings) |
146 | pr_info("Future hung task reports are suppressed, see sysctl kernel.hung_task_warnings\n" ); |
147 | } |
148 | |
149 | touch_nmi_watchdog(); |
150 | } |
151 | |
152 | /* |
153 | * To avoid extending the RCU grace period for an unbounded amount of time, |
154 | * periodically exit the critical section and enter a new one. |
155 | * |
156 | * For preemptible RCU it is sufficient to call rcu_read_unlock in order |
157 | * to exit the grace period. For classic RCU, a reschedule is required. |
158 | */ |
159 | static bool rcu_lock_break(struct task_struct *g, struct task_struct *t) |
160 | { |
161 | bool can_cont; |
162 | |
163 | get_task_struct(t: g); |
164 | get_task_struct(t); |
165 | rcu_read_unlock(); |
166 | cond_resched(); |
167 | rcu_read_lock(); |
168 | can_cont = pid_alive(p: g) && pid_alive(p: t); |
169 | put_task_struct(t); |
170 | put_task_struct(t: g); |
171 | |
172 | return can_cont; |
173 | } |
174 | |
175 | /* |
176 | * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for |
177 | * a really long time (120 seconds). If that happens, print out |
178 | * a warning. |
179 | */ |
180 | static void check_hung_uninterruptible_tasks(unsigned long timeout) |
181 | { |
182 | int max_count = sysctl_hung_task_check_count; |
183 | unsigned long last_break = jiffies; |
184 | struct task_struct *g, *t; |
185 | |
186 | /* |
187 | * If the system crashed already then all bets are off, |
188 | * do not report extra hung tasks: |
189 | */ |
190 | if (test_taint(TAINT_DIE) || did_panic) |
191 | return; |
192 | |
193 | hung_task_show_lock = false; |
194 | rcu_read_lock(); |
195 | for_each_process_thread(g, t) { |
196 | unsigned int state; |
197 | |
198 | if (!max_count--) |
199 | goto unlock; |
200 | if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) { |
201 | if (!rcu_lock_break(g, t)) |
202 | goto unlock; |
203 | last_break = jiffies; |
204 | } |
205 | /* |
206 | * skip the TASK_KILLABLE tasks -- these can be killed |
207 | * skip the TASK_IDLE tasks -- those are genuinely idle |
208 | */ |
209 | state = READ_ONCE(t->__state); |
210 | if ((state & TASK_UNINTERRUPTIBLE) && |
211 | !(state & TASK_WAKEKILL) && |
212 | !(state & TASK_NOLOAD)) |
213 | check_hung_task(t, timeout); |
214 | } |
215 | unlock: |
216 | rcu_read_unlock(); |
217 | if (hung_task_show_lock) |
218 | debug_show_all_locks(); |
219 | |
220 | if (hung_task_show_all_bt) { |
221 | hung_task_show_all_bt = false; |
222 | trigger_all_cpu_backtrace(); |
223 | } |
224 | |
225 | if (hung_task_call_panic) |
226 | panic(fmt: "hung_task: blocked tasks" ); |
227 | } |
228 | |
229 | static long hung_timeout_jiffies(unsigned long last_checked, |
230 | unsigned long timeout) |
231 | { |
232 | /* timeout of 0 will disable the watchdog */ |
233 | return timeout ? last_checked - jiffies + timeout * HZ : |
234 | MAX_SCHEDULE_TIMEOUT; |
235 | } |
236 | |
237 | #ifdef CONFIG_SYSCTL |
238 | /* |
239 | * Process updating of timeout sysctl |
240 | */ |
241 | static int proc_dohung_task_timeout_secs(struct ctl_table *table, int write, |
242 | void *buffer, |
243 | size_t *lenp, loff_t *ppos) |
244 | { |
245 | int ret; |
246 | |
247 | ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); |
248 | |
249 | if (ret || !write) |
250 | goto out; |
251 | |
252 | wake_up_process(tsk: watchdog_task); |
253 | |
254 | out: |
255 | return ret; |
256 | } |
257 | |
258 | /* |
259 | * This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs |
260 | * and hung_task_check_interval_secs |
261 | */ |
262 | static const unsigned long hung_task_timeout_max = (LONG_MAX / HZ); |
263 | static struct ctl_table hung_task_sysctls[] = { |
264 | #ifdef CONFIG_SMP |
265 | { |
266 | .procname = "hung_task_all_cpu_backtrace" , |
267 | .data = &sysctl_hung_task_all_cpu_backtrace, |
268 | .maxlen = sizeof(int), |
269 | .mode = 0644, |
270 | .proc_handler = proc_dointvec_minmax, |
271 | .extra1 = SYSCTL_ZERO, |
272 | .extra2 = SYSCTL_ONE, |
273 | }, |
274 | #endif /* CONFIG_SMP */ |
275 | { |
276 | .procname = "hung_task_panic" , |
277 | .data = &sysctl_hung_task_panic, |
278 | .maxlen = sizeof(int), |
279 | .mode = 0644, |
280 | .proc_handler = proc_dointvec_minmax, |
281 | .extra1 = SYSCTL_ZERO, |
282 | .extra2 = SYSCTL_ONE, |
283 | }, |
284 | { |
285 | .procname = "hung_task_check_count" , |
286 | .data = &sysctl_hung_task_check_count, |
287 | .maxlen = sizeof(int), |
288 | .mode = 0644, |
289 | .proc_handler = proc_dointvec_minmax, |
290 | .extra1 = SYSCTL_ZERO, |
291 | }, |
292 | { |
293 | .procname = "hung_task_timeout_secs" , |
294 | .data = &sysctl_hung_task_timeout_secs, |
295 | .maxlen = sizeof(unsigned long), |
296 | .mode = 0644, |
297 | .proc_handler = proc_dohung_task_timeout_secs, |
298 | .extra2 = (void *)&hung_task_timeout_max, |
299 | }, |
300 | { |
301 | .procname = "hung_task_check_interval_secs" , |
302 | .data = &sysctl_hung_task_check_interval_secs, |
303 | .maxlen = sizeof(unsigned long), |
304 | .mode = 0644, |
305 | .proc_handler = proc_dohung_task_timeout_secs, |
306 | .extra2 = (void *)&hung_task_timeout_max, |
307 | }, |
308 | { |
309 | .procname = "hung_task_warnings" , |
310 | .data = &sysctl_hung_task_warnings, |
311 | .maxlen = sizeof(int), |
312 | .mode = 0644, |
313 | .proc_handler = proc_dointvec_minmax, |
314 | .extra1 = SYSCTL_NEG_ONE, |
315 | }, |
316 | {} |
317 | }; |
318 | |
319 | static void __init hung_task_sysctl_init(void) |
320 | { |
321 | register_sysctl_init("kernel" , hung_task_sysctls); |
322 | } |
323 | #else |
324 | #define hung_task_sysctl_init() do { } while (0) |
325 | #endif /* CONFIG_SYSCTL */ |
326 | |
327 | |
328 | static atomic_t reset_hung_task = ATOMIC_INIT(0); |
329 | |
330 | void reset_hung_task_detector(void) |
331 | { |
332 | atomic_set(v: &reset_hung_task, i: 1); |
333 | } |
334 | EXPORT_SYMBOL_GPL(reset_hung_task_detector); |
335 | |
336 | static bool hung_detector_suspended; |
337 | |
338 | static int hungtask_pm_notify(struct notifier_block *self, |
339 | unsigned long action, void *hcpu) |
340 | { |
341 | switch (action) { |
342 | case PM_SUSPEND_PREPARE: |
343 | case PM_HIBERNATION_PREPARE: |
344 | case PM_RESTORE_PREPARE: |
345 | hung_detector_suspended = true; |
346 | break; |
347 | case PM_POST_SUSPEND: |
348 | case PM_POST_HIBERNATION: |
349 | case PM_POST_RESTORE: |
350 | hung_detector_suspended = false; |
351 | break; |
352 | default: |
353 | break; |
354 | } |
355 | return NOTIFY_OK; |
356 | } |
357 | |
358 | /* |
359 | * kthread which checks for tasks stuck in D state |
360 | */ |
361 | static int watchdog(void *dummy) |
362 | { |
363 | unsigned long hung_last_checked = jiffies; |
364 | |
365 | set_user_nice(current, nice: 0); |
366 | |
367 | for ( ; ; ) { |
368 | unsigned long timeout = sysctl_hung_task_timeout_secs; |
369 | unsigned long interval = sysctl_hung_task_check_interval_secs; |
370 | long t; |
371 | |
372 | if (interval == 0) |
373 | interval = timeout; |
374 | interval = min_t(unsigned long, interval, timeout); |
375 | t = hung_timeout_jiffies(last_checked: hung_last_checked, timeout: interval); |
376 | if (t <= 0) { |
377 | if (!atomic_xchg(v: &reset_hung_task, new: 0) && |
378 | !hung_detector_suspended) |
379 | check_hung_uninterruptible_tasks(timeout); |
380 | hung_last_checked = jiffies; |
381 | continue; |
382 | } |
383 | schedule_timeout_interruptible(timeout: t); |
384 | } |
385 | |
386 | return 0; |
387 | } |
388 | |
389 | static int __init hung_task_init(void) |
390 | { |
391 | atomic_notifier_chain_register(nh: &panic_notifier_list, nb: &panic_block); |
392 | |
393 | /* Disable hung task detector on suspend */ |
394 | pm_notifier(hungtask_pm_notify, 0); |
395 | |
396 | watchdog_task = kthread_run(watchdog, NULL, "khungtaskd" ); |
397 | hung_task_sysctl_init(); |
398 | |
399 | return 0; |
400 | } |
401 | subsys_initcall(hung_task_init); |
402 | |