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/sysctl.h>
19 #include <linux/suspend.h>
20 #include <linux/utsname.h>
21 #include <linux/sched/signal.h>
22 #include <linux/sched/debug.h>
23 #include <linux/sched/sysctl.h>
24
25 #include <trace/events/sched.h>
26
27 /*
28 * The number of tasks checked:
29 */
30 int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
31
32 /*
33 * Limit number of tasks checked in a batch.
34 *
35 * This value controls the preemptibility of khungtaskd since preemption
36 * is disabled during the critical section. It also controls the size of
37 * the RCU grace period. So it needs to be upper-bound.
38 */
39 #define HUNG_TASK_LOCK_BREAK (HZ / 10)
40
41 /*
42 * Zero means infinite timeout - no checking done:
43 */
44 unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
45
46 /*
47 * Zero (default value) means use sysctl_hung_task_timeout_secs:
48 */
49 unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
50
51 int __read_mostly sysctl_hung_task_warnings = 10;
52
53 static int __read_mostly did_panic;
54 static bool hung_task_show_lock;
55 static bool hung_task_call_panic;
56
57 static struct task_struct *watchdog_task;
58
59 /*
60 * Should we panic (and reboot, if panic_timeout= is set) when a
61 * hung task is detected:
62 */
63 unsigned int __read_mostly sysctl_hung_task_panic =
64 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
65
hung_task_panic_setup(char * str)66 static int __init hung_task_panic_setup(char *str)
67 {
68 int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
69
70 if (rc)
71 return rc;
72 return 1;
73 }
74 __setup("hung_task_panic=", hung_task_panic_setup);
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
142 touch_nmi_watchdog();
143 }
144
145 /*
146 * To avoid extending the RCU grace period for an unbounded amount of time,
147 * periodically exit the critical section and enter a new one.
148 *
149 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
150 * to exit the grace period. For classic RCU, a reschedule is required.
151 */
rcu_lock_break(struct task_struct * g,struct task_struct * t)152 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
153 {
154 bool can_cont;
155
156 get_task_struct(g);
157 get_task_struct(t);
158 rcu_read_unlock();
159 cond_resched();
160 rcu_read_lock();
161 can_cont = pid_alive(g) && pid_alive(t);
162 put_task_struct(t);
163 put_task_struct(g);
164
165 return can_cont;
166 }
167
168 /*
169 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
170 * a really long time (120 seconds). If that happens, print out
171 * a warning.
172 */
check_hung_uninterruptible_tasks(unsigned long timeout)173 static void check_hung_uninterruptible_tasks(unsigned long timeout)
174 {
175 int max_count = sysctl_hung_task_check_count;
176 unsigned long last_break = jiffies;
177 struct task_struct *g, *t;
178
179 /*
180 * If the system crashed already then all bets are off,
181 * do not report extra hung tasks:
182 */
183 if (test_taint(TAINT_DIE) || did_panic)
184 return;
185
186 hung_task_show_lock = false;
187 rcu_read_lock();
188 for_each_process_thread(g, t) {
189 if (!max_count--)
190 goto unlock;
191 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
192 if (!rcu_lock_break(g, t))
193 goto unlock;
194 last_break = jiffies;
195 }
196 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
197 if (t->state == TASK_UNINTERRUPTIBLE)
198 check_hung_task(t, timeout);
199 }
200 unlock:
201 rcu_read_unlock();
202 if (hung_task_show_lock)
203 debug_show_all_locks();
204 if (hung_task_call_panic) {
205 trigger_all_cpu_backtrace();
206 panic("hung_task: blocked tasks");
207 }
208 }
209
hung_timeout_jiffies(unsigned long last_checked,unsigned long timeout)210 static long hung_timeout_jiffies(unsigned long last_checked,
211 unsigned long timeout)
212 {
213 /* timeout of 0 will disable the watchdog */
214 return timeout ? last_checked - jiffies + timeout * HZ :
215 MAX_SCHEDULE_TIMEOUT;
216 }
217
218 /*
219 * Process updating of timeout sysctl
220 */
proc_dohung_task_timeout_secs(struct ctl_table * table,int write,void __user * buffer,size_t * lenp,loff_t * ppos)221 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
222 void __user *buffer,
223 size_t *lenp, loff_t *ppos)
224 {
225 int ret;
226
227 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
228
229 if (ret || !write)
230 goto out;
231
232 wake_up_process(watchdog_task);
233
234 out:
235 return ret;
236 }
237
238 static atomic_t reset_hung_task = ATOMIC_INIT(0);
239
reset_hung_task_detector(void)240 void reset_hung_task_detector(void)
241 {
242 atomic_set(&reset_hung_task, 1);
243 }
244 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
245
246 static bool hung_detector_suspended;
247
hungtask_pm_notify(struct notifier_block * self,unsigned long action,void * hcpu)248 static int hungtask_pm_notify(struct notifier_block *self,
249 unsigned long action, void *hcpu)
250 {
251 switch (action) {
252 case PM_SUSPEND_PREPARE:
253 case PM_HIBERNATION_PREPARE:
254 case PM_RESTORE_PREPARE:
255 hung_detector_suspended = true;
256 break;
257 case PM_POST_SUSPEND:
258 case PM_POST_HIBERNATION:
259 case PM_POST_RESTORE:
260 hung_detector_suspended = false;
261 break;
262 default:
263 break;
264 }
265 return NOTIFY_OK;
266 }
267
268 /*
269 * kthread which checks for tasks stuck in D state
270 */
watchdog(void * dummy)271 static int watchdog(void *dummy)
272 {
273 unsigned long hung_last_checked = jiffies;
274
275 set_user_nice(current, 0);
276
277 for ( ; ; ) {
278 unsigned long timeout = sysctl_hung_task_timeout_secs;
279 unsigned long interval = sysctl_hung_task_check_interval_secs;
280 long t;
281
282 if (interval == 0)
283 interval = timeout;
284 interval = min_t(unsigned long, interval, timeout);
285 t = hung_timeout_jiffies(hung_last_checked, interval);
286 if (t <= 0) {
287 if (!atomic_xchg(&reset_hung_task, 0) &&
288 !hung_detector_suspended)
289 check_hung_uninterruptible_tasks(timeout);
290 hung_last_checked = jiffies;
291 continue;
292 }
293 schedule_timeout_interruptible(t);
294 }
295
296 return 0;
297 }
298
hung_task_init(void)299 static int __init hung_task_init(void)
300 {
301 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
302
303 /* Disable hung task detector on suspend */
304 pm_notifier(hungtask_pm_notify, 0);
305
306 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
307
308 return 0;
309 }
310 subsys_initcall(hung_task_init);
311
