Merge branch 'for-5.11/i2c-hid' into for-linus
[linux-2.6-microblaze.git] / kernel / hung_task.c
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 static bool hung_task_show_all_bt;
57
58 static struct task_struct *watchdog_task;
59
60 #ifdef CONFIG_SMP
61 /*
62  * Should we dump all CPUs backtraces in a hung task event?
63  * Defaults to 0, can be changed via sysctl.
64  */
65 unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace;
66 #endif /* CONFIG_SMP */
67
68 /*
69  * Should we panic (and reboot, if panic_timeout= is set) when a
70  * hung task is detected:
71  */
72 unsigned int __read_mostly sysctl_hung_task_panic =
73                                 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
74
75 static int
76 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
77 {
78         did_panic = 1;
79
80         return NOTIFY_DONE;
81 }
82
83 static struct notifier_block panic_block = {
84         .notifier_call = hung_task_panic,
85 };
86
87 static void check_hung_task(struct task_struct *t, unsigned long timeout)
88 {
89         unsigned long switch_count = t->nvcsw + t->nivcsw;
90
91         /*
92          * Ensure the task is not frozen.
93          * Also, skip vfork and any other user process that freezer should skip.
94          */
95         if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
96             return;
97
98         /*
99          * When a freshly created task is scheduled once, changes its state to
100          * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
101          * musn't be checked.
102          */
103         if (unlikely(!switch_count))
104                 return;
105
106         if (switch_count != t->last_switch_count) {
107                 t->last_switch_count = switch_count;
108                 t->last_switch_time = jiffies;
109                 return;
110         }
111         if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
112                 return;
113
114         trace_sched_process_hang(t);
115
116         if (sysctl_hung_task_panic) {
117                 console_verbose();
118                 hung_task_show_lock = true;
119                 hung_task_call_panic = true;
120         }
121
122         /*
123          * Ok, the task did not get scheduled for more than 2 minutes,
124          * complain:
125          */
126         if (sysctl_hung_task_warnings) {
127                 if (sysctl_hung_task_warnings > 0)
128                         sysctl_hung_task_warnings--;
129                 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
130                        t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
131                 pr_err("      %s %s %.*s\n",
132                         print_tainted(), init_utsname()->release,
133                         (int)strcspn(init_utsname()->version, " "),
134                         init_utsname()->version);
135                 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
136                         " disables this message.\n");
137                 sched_show_task(t);
138                 hung_task_show_lock = true;
139
140                 if (sysctl_hung_task_all_cpu_backtrace)
141                         hung_task_show_all_bt = true;
142         }
143
144         touch_nmi_watchdog();
145 }
146
147 /*
148  * To avoid extending the RCU grace period for an unbounded amount of time,
149  * periodically exit the critical section and enter a new one.
150  *
151  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
152  * to exit the grace period. For classic RCU, a reschedule is required.
153  */
154 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
155 {
156         bool can_cont;
157
158         get_task_struct(g);
159         get_task_struct(t);
160         rcu_read_unlock();
161         cond_resched();
162         rcu_read_lock();
163         can_cont = pid_alive(g) && pid_alive(t);
164         put_task_struct(t);
165         put_task_struct(g);
166
167         return can_cont;
168 }
169
170 /*
171  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
172  * a really long time (120 seconds). If that happens, print out
173  * a warning.
174  */
175 static void check_hung_uninterruptible_tasks(unsigned long timeout)
176 {
177         int max_count = sysctl_hung_task_check_count;
178         unsigned long last_break = jiffies;
179         struct task_struct *g, *t;
180
181         /*
182          * If the system crashed already then all bets are off,
183          * do not report extra hung tasks:
184          */
185         if (test_taint(TAINT_DIE) || did_panic)
186                 return;
187
188         hung_task_show_lock = false;
189         rcu_read_lock();
190         for_each_process_thread(g, t) {
191                 if (!max_count--)
192                         goto unlock;
193                 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
194                         if (!rcu_lock_break(g, t))
195                                 goto unlock;
196                         last_break = jiffies;
197                 }
198                 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
199                 if (t->state == TASK_UNINTERRUPTIBLE)
200                         check_hung_task(t, timeout);
201         }
202  unlock:
203         rcu_read_unlock();
204         if (hung_task_show_lock)
205                 debug_show_all_locks();
206
207         if (hung_task_show_all_bt) {
208                 hung_task_show_all_bt = false;
209                 trigger_all_cpu_backtrace();
210         }
211
212         if (hung_task_call_panic)
213                 panic("hung_task: blocked tasks");
214 }
215
216 static long hung_timeout_jiffies(unsigned long last_checked,
217                                  unsigned long timeout)
218 {
219         /* timeout of 0 will disable the watchdog */
220         return timeout ? last_checked - jiffies + timeout * HZ :
221                 MAX_SCHEDULE_TIMEOUT;
222 }
223
224 /*
225  * Process updating of timeout sysctl
226  */
227 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
228                                   void *buffer, size_t *lenp, loff_t *ppos)
229 {
230         int ret;
231
232         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
233
234         if (ret || !write)
235                 goto out;
236
237         wake_up_process(watchdog_task);
238
239  out:
240         return ret;
241 }
242
243 static atomic_t reset_hung_task = ATOMIC_INIT(0);
244
245 void reset_hung_task_detector(void)
246 {
247         atomic_set(&reset_hung_task, 1);
248 }
249 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
250
251 static bool hung_detector_suspended;
252
253 static int hungtask_pm_notify(struct notifier_block *self,
254                               unsigned long action, void *hcpu)
255 {
256         switch (action) {
257         case PM_SUSPEND_PREPARE:
258         case PM_HIBERNATION_PREPARE:
259         case PM_RESTORE_PREPARE:
260                 hung_detector_suspended = true;
261                 break;
262         case PM_POST_SUSPEND:
263         case PM_POST_HIBERNATION:
264         case PM_POST_RESTORE:
265                 hung_detector_suspended = false;
266                 break;
267         default:
268                 break;
269         }
270         return NOTIFY_OK;
271 }
272
273 /*
274  * kthread which checks for tasks stuck in D state
275  */
276 static int watchdog(void *dummy)
277 {
278         unsigned long hung_last_checked = jiffies;
279
280         set_user_nice(current, 0);
281
282         for ( ; ; ) {
283                 unsigned long timeout = sysctl_hung_task_timeout_secs;
284                 unsigned long interval = sysctl_hung_task_check_interval_secs;
285                 long t;
286
287                 if (interval == 0)
288                         interval = timeout;
289                 interval = min_t(unsigned long, interval, timeout);
290                 t = hung_timeout_jiffies(hung_last_checked, interval);
291                 if (t <= 0) {
292                         if (!atomic_xchg(&reset_hung_task, 0) &&
293                             !hung_detector_suspended)
294                                 check_hung_uninterruptible_tasks(timeout);
295                         hung_last_checked = jiffies;
296                         continue;
297                 }
298                 schedule_timeout_interruptible(t);
299         }
300
301         return 0;
302 }
303
304 static int __init hung_task_init(void)
305 {
306         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
307
308         /* Disable hung task detector on suspend */
309         pm_notifier(hungtask_pm_notify, 0);
310
311         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
312
313         return 0;
314 }
315 subsys_initcall(hung_task_init);