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 #ifdef CONFIG_DFX_HUNGTASK
28 #include <dfx/hungtask_base.h>
29 #endif
30
31 /*
32 * The number of tasks checked:
33 */
34 int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
35
36 /*
37 * Limit number of tasks checked in a batch.
38 *
39 * This value controls the preemptibility of khungtaskd since preemption
40 * is disabled during the critical section. It also controls the size of
41 * the RCU grace period. So it needs to be upper-bound.
42 */
43 #define HUNG_TASK_LOCK_BREAK (HZ / 10)
44
45 /*
46 * Zero means infinite timeout - no checking done:
47 */
48 unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
49
50 /*
51 * Zero (default value) means use sysctl_hung_task_timeout_secs:
52 */
53 unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
54
55 int __read_mostly sysctl_hung_task_warnings = 10;
56
57 static int __read_mostly did_panic;
58 #ifndef CONFIG_DFX_HUNGTASK
59 static bool hung_task_show_lock;
60 static bool hung_task_call_panic;
61 static bool hung_task_show_all_bt;
62 #endif
63
64 static struct task_struct *watchdog_task;
65
66 #ifdef CONFIG_SMP
67 /*
68 * Should we dump all CPUs backtraces in a hung task event?
69 * Defaults to 0, can be changed via sysctl.
70 */
71 unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace;
72 #endif /* CONFIG_SMP */
73
74 /*
75 * Should we panic (and reboot, if panic_timeout= is set) when a
76 * hung task is detected:
77 */
78 unsigned int __read_mostly sysctl_hung_task_panic =
79 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
80
81 static int
hung_task_panic(struct notifier_block * this,unsigned long event,void * ptr)82 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
83 {
84 did_panic = 1;
85 #ifdef CONFIG_DFX_HUNGTASK
86 htbase_set_panic(did_panic);
87 #endif
88 return NOTIFY_DONE;
89 }
90
91 static struct notifier_block panic_block = {
92 .notifier_call = hung_task_panic,
93 };
94
95 #ifndef CONFIG_DFX_HUNGTASK
check_hung_task(struct task_struct * t,unsigned long timeout)96 static void check_hung_task(struct task_struct *t, unsigned long timeout)
97 {
98 unsigned long switch_count = t->nvcsw + t->nivcsw;
99
100 /*
101 * Ensure the task is not frozen.
102 * Also, skip vfork and any other user process that freezer should skip.
103 */
104 if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
105 return;
106
107 /*
108 * When a freshly created task is scheduled once, changes its state to
109 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
110 * musn't be checked.
111 */
112 if (unlikely(!switch_count))
113 return;
114
115 if (switch_count != t->last_switch_count) {
116 t->last_switch_count = switch_count;
117 t->last_switch_time = jiffies;
118 return;
119 }
120 if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
121 return;
122
123 trace_sched_process_hang(t);
124
125 if (sysctl_hung_task_panic) {
126 console_verbose();
127 hung_task_show_lock = true;
128 hung_task_call_panic = true;
129 }
130
131 /*
132 * Ok, the task did not get scheduled for more than 2 minutes,
133 * complain:
134 */
135 if (sysctl_hung_task_warnings) {
136 if (sysctl_hung_task_warnings > 0)
137 sysctl_hung_task_warnings--;
138 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
139 t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
140 pr_err(" %s %s %.*s\n",
141 print_tainted(), init_utsname()->release,
142 (int)strcspn(init_utsname()->version, " "),
143 init_utsname()->version);
144 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
145 " disables this message.\n");
146 sched_show_task(t);
147 hung_task_show_lock = true;
148
149 if (sysctl_hung_task_all_cpu_backtrace)
150 hung_task_show_all_bt = true;
151 }
152
153 touch_nmi_watchdog();
154 }
155
156 /*
157 * To avoid extending the RCU grace period for an unbounded amount of time,
158 * periodically exit the critical section and enter a new one.
159 *
160 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
161 * to exit the grace period. For classic RCU, a reschedule is required.
162 */
rcu_lock_break(struct task_struct * g,struct task_struct * t)163 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
164 {
165 bool can_cont;
166
167 get_task_struct(g);
168 get_task_struct(t);
169 rcu_read_unlock();
170 cond_resched();
171 rcu_read_lock();
172 can_cont = pid_alive(g) && pid_alive(t);
173 put_task_struct(t);
174 put_task_struct(g);
175
176 return can_cont;
177 }
178
179 /*
180 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
181 * a really long time (120 seconds). If that happens, print out
182 * a warning.
183 */
check_hung_uninterruptible_tasks(unsigned long timeout)184 static void check_hung_uninterruptible_tasks(unsigned long timeout)
185 {
186 int max_count = sysctl_hung_task_check_count;
187 unsigned long last_break = jiffies;
188 struct task_struct *g, *t;
189
190 /*
191 * If the system crashed already then all bets are off,
192 * do not report extra hung tasks:
193 */
194 if (test_taint(TAINT_DIE) || did_panic)
195 return;
196
197 hung_task_show_lock = false;
198 rcu_read_lock();
199 for_each_process_thread(g, t) {
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 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
208 if (t->state == TASK_UNINTERRUPTIBLE)
209 check_hung_task(t, timeout);
210 }
211 unlock:
212 rcu_read_unlock();
213 if (hung_task_show_lock)
214 debug_show_all_locks();
215
216 if (hung_task_show_all_bt) {
217 hung_task_show_all_bt = false;
218 trigger_all_cpu_backtrace();
219 }
220
221 if (hung_task_call_panic)
222 panic("hung_task: blocked tasks");
223 }
224 #endif
225
hung_timeout_jiffies(unsigned long last_checked,unsigned long timeout)226 static long hung_timeout_jiffies(unsigned long last_checked,
227 unsigned long timeout)
228 {
229 /* timeout of 0 will disable the watchdog */
230 return timeout ? last_checked - jiffies + timeout * HZ :
231 MAX_SCHEDULE_TIMEOUT;
232 }
233
234 /*
235 * Process updating of timeout sysctl
236 */
proc_dohung_task_timeout_secs(struct ctl_table * table,int write,void * buffer,size_t * lenp,loff_t * ppos)237 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
238 void *buffer, size_t *lenp, loff_t *ppos)
239 {
240 int ret;
241
242 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
243
244 if (ret || !write)
245 goto out;
246
247 wake_up_process(watchdog_task);
248 #ifdef CONFIG_DFX_HUNGTASK
249 htbase_set_timeout_secs(sysctl_hung_task_timeout_secs);
250 #endif
251 out:
252 return ret;
253 }
254
255 static atomic_t reset_hung_task = ATOMIC_INIT(0);
256
reset_hung_task_detector(void)257 void reset_hung_task_detector(void)
258 {
259 atomic_set(&reset_hung_task, 1);
260 }
261 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
262
263 static bool hung_detector_suspended;
264
hungtask_pm_notify(struct notifier_block * self,unsigned long action,void * hcpu)265 static int hungtask_pm_notify(struct notifier_block *self,
266 unsigned long action, void *hcpu)
267 {
268 switch (action) {
269 case PM_SUSPEND_PREPARE:
270 case PM_HIBERNATION_PREPARE:
271 case PM_RESTORE_PREPARE:
272 hung_detector_suspended = true;
273 break;
274 case PM_POST_SUSPEND:
275 case PM_POST_HIBERNATION:
276 case PM_POST_RESTORE:
277 hung_detector_suspended = false;
278 break;
279 default:
280 break;
281 }
282 return NOTIFY_OK;
283 }
284
285 /*
286 * kthread which checks for tasks stuck in D state
287 */
watchdog(void * dummy)288 static int watchdog(void *dummy)
289 {
290 unsigned long hung_last_checked = jiffies;
291
292 set_user_nice(current, 0);
293
294 for ( ; ; ) {
295 #ifdef CONFIG_DFX_HUNGTASK
296 unsigned long timeout = HEARTBEAT_TIME;
297 #else
298 unsigned long timeout = sysctl_hung_task_timeout_secs;
299 #endif
300 unsigned long interval = sysctl_hung_task_check_interval_secs;
301 long t;
302
303 if (interval == 0)
304 interval = timeout;
305 timeout = min_t(unsigned long, interval, timeout);
306 t = hung_timeout_jiffies(hung_last_checked, timeout);
307 if (t <= 0) {
308 if (!atomic_xchg(&reset_hung_task, 0) &&
309 !hung_detector_suspended)
310 #ifdef CONFIG_DFX_HUNGTASK
311 htbase_check_tasks(timeout);
312 #else
313 check_hung_uninterruptible_tasks(timeout);
314 #endif
315 hung_last_checked = jiffies;
316 continue;
317 }
318 schedule_timeout_interruptible(t);
319 }
320
321 return 0;
322 }
323
hung_task_init(void)324 static int __init hung_task_init(void)
325 {
326 #ifdef CONFIG_DFX_HUNGTASK
327 int ret = 0;
328
329 ret = htbase_create_sysfs();
330 if (ret)
331 pr_err("hungtask: create_sysfs_hungtask fail");
332 #endif
333 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
334
335 /* Disable hung task detector on suspend */
336 pm_notifier(hungtask_pm_notify, 0);
337
338 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
339
340 return 0;
341 }
342 subsys_initcall(hung_task_init);
343