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 unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace;
67 #endif /* CONFIG_SMP */
68
69 /*
70 * Should we panic (and reboot, if panic_timeout= is set) when a
71 * hung task is detected:
72 */
73 unsigned int __read_mostly sysctl_hung_task_panic =
74 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
75
76 static int
hung_task_panic(struct notifier_block * this,unsigned long event,void * ptr)77 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
78 {
79 did_panic = 1;
80
81 return NOTIFY_DONE;
82 }
83
84 static struct notifier_block panic_block = {
85 .notifier_call = hung_task_panic,
86 };
87
check_hung_task(struct task_struct * t,unsigned long timeout)88 static void check_hung_task(struct task_struct *t, unsigned long timeout)
89 {
90 unsigned long switch_count = t->nvcsw + t->nivcsw;
91
92 /*
93 * Ensure the task is not frozen.
94 * Also, skip vfork and any other user process that freezer should skip.
95 */
96 if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
97 return;
98
99 /*
100 * When a freshly created task is scheduled once, changes its state to
101 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
102 * musn't be checked.
103 */
104 if (unlikely(!switch_count))
105 return;
106
107 if (switch_count != t->last_switch_count) {
108 t->last_switch_count = switch_count;
109 t->last_switch_time = jiffies;
110 return;
111 }
112 if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
113 return;
114
115 trace_sched_process_hang(t);
116
117 if (sysctl_hung_task_panic) {
118 console_verbose();
119 hung_task_show_lock = true;
120 hung_task_call_panic = true;
121 }
122
123 /*
124 * Ok, the task did not get scheduled for more than 2 minutes,
125 * complain:
126 */
127 if (sysctl_hung_task_warnings) {
128 if (sysctl_hung_task_warnings > 0)
129 sysctl_hung_task_warnings--;
130 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
131 t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
132 pr_err(" %s %s %.*s\n",
133 print_tainted(), init_utsname()->release,
134 (int)strcspn(init_utsname()->version, " "),
135 init_utsname()->version);
136 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
137 " disables this message.\n");
138 sched_show_task(t);
139 hung_task_show_lock = true;
140
141 if (sysctl_hung_task_all_cpu_backtrace)
142 hung_task_show_all_bt = true;
143 }
144
145 touch_nmi_watchdog();
146 }
147
148 /*
149 * To avoid extending the RCU grace period for an unbounded amount of time,
150 * periodically exit the critical section and enter a new one.
151 *
152 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
153 * to exit the grace period. For classic RCU, a reschedule is required.
154 */
rcu_lock_break(struct task_struct * g,struct task_struct * t)155 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
156 {
157 bool can_cont;
158
159 get_task_struct(g);
160 get_task_struct(t);
161 rcu_read_unlock();
162 cond_resched();
163 rcu_read_lock();
164 can_cont = pid_alive(g) && pid_alive(t);
165 put_task_struct(t);
166 put_task_struct(g);
167
168 return can_cont;
169 }
170
171 /*
172 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
173 * a really long time (120 seconds). If that happens, print out
174 * a warning.
175 */
check_hung_uninterruptible_tasks(unsigned long timeout)176 static void check_hung_uninterruptible_tasks(unsigned long timeout)
177 {
178 int max_count = sysctl_hung_task_check_count;
179 unsigned long last_break = jiffies;
180 struct task_struct *g, *t;
181
182 /*
183 * If the system crashed already then all bets are off,
184 * do not report extra hung tasks:
185 */
186 if (test_taint(TAINT_DIE) || did_panic)
187 return;
188
189 hung_task_show_lock = false;
190 rcu_read_lock();
191 for_each_process_thread(g, t) {
192 if (!max_count--)
193 goto unlock;
194 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
195 if (!rcu_lock_break(g, t))
196 goto unlock;
197 last_break = jiffies;
198 }
199 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
200 if (READ_ONCE(t->__state) == TASK_UNINTERRUPTIBLE)
201 check_hung_task(t, timeout);
202 }
203 unlock:
204 rcu_read_unlock();
205 if (hung_task_show_lock)
206 debug_show_all_locks();
207
208 if (hung_task_show_all_bt) {
209 hung_task_show_all_bt = false;
210 trigger_all_cpu_backtrace();
211 }
212
213 if (hung_task_call_panic)
214 panic("hung_task: blocked tasks");
215 }
216
hung_timeout_jiffies(unsigned long last_checked,unsigned long timeout)217 static long hung_timeout_jiffies(unsigned long last_checked,
218 unsigned long timeout)
219 {
220 /* timeout of 0 will disable the watchdog */
221 return timeout ? last_checked - jiffies + timeout * HZ :
222 MAX_SCHEDULE_TIMEOUT;
223 }
224
225 /*
226 * Process updating of timeout sysctl
227 */
proc_dohung_task_timeout_secs(struct ctl_table * table,int write,void * buffer,size_t * lenp,loff_t * ppos)228 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
229 void *buffer, size_t *lenp, loff_t *ppos)
230 {
231 int ret;
232
233 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
234
235 if (ret || !write)
236 goto out;
237
238 wake_up_process(watchdog_task);
239
240 out:
241 return ret;
242 }
243
244 static atomic_t reset_hung_task = ATOMIC_INIT(0);
245
reset_hung_task_detector(void)246 void reset_hung_task_detector(void)
247 {
248 atomic_set(&reset_hung_task, 1);
249 }
250 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
251
252 static bool hung_detector_suspended;
253
hungtask_pm_notify(struct notifier_block * self,unsigned long action,void * hcpu)254 static int hungtask_pm_notify(struct notifier_block *self,
255 unsigned long action, void *hcpu)
256 {
257 switch (action) {
258 case PM_SUSPEND_PREPARE:
259 case PM_HIBERNATION_PREPARE:
260 case PM_RESTORE_PREPARE:
261 hung_detector_suspended = true;
262 break;
263 case PM_POST_SUSPEND:
264 case PM_POST_HIBERNATION:
265 case PM_POST_RESTORE:
266 hung_detector_suspended = false;
267 break;
268 default:
269 break;
270 }
271 return NOTIFY_OK;
272 }
273
274 /*
275 * kthread which checks for tasks stuck in D state
276 */
watchdog(void * dummy)277 static int watchdog(void *dummy)
278 {
279 unsigned long hung_last_checked = jiffies;
280
281 set_user_nice(current, 0);
282
283 for ( ; ; ) {
284 unsigned long timeout = sysctl_hung_task_timeout_secs;
285 unsigned long interval = sysctl_hung_task_check_interval_secs;
286 long t;
287
288 if (interval == 0)
289 interval = timeout;
290 interval = min_t(unsigned long, interval, timeout);
291 t = hung_timeout_jiffies(hung_last_checked, interval);
292 if (t <= 0) {
293 if (!atomic_xchg(&reset_hung_task, 0) &&
294 !hung_detector_suspended)
295 check_hung_uninterruptible_tasks(timeout);
296 hung_last_checked = jiffies;
297 continue;
298 }
299 schedule_timeout_interruptible(t);
300 }
301
302 return 0;
303 }
304
hung_task_init(void)305 static int __init hung_task_init(void)
306 {
307 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
308
309 /* Disable hung task detector on suspend */
310 pm_notifier(hungtask_pm_notify, 0);
311
312 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
313
314 return 0;
315 }
316 subsys_initcall(hung_task_init);
317