1/*
2 * Detect Hung Task
3 *
4 * kernel/hung_task.c - kernel thread for detecting tasks stuck in D state
5 *
6 */
7
8#include <linux/mm.h>
9#include <linux/cpu.h>
10#include <linux/nmi.h>
11#include <linux/init.h>
12#include <linux/delay.h>
13#include <linux/freezer.h>
14#include <linux/kthread.h>
15#include <linux/lockdep.h>
16#include <linux/export.h>
17#include <linux/sysctl.h>
18#include <linux/utsname.h>
19#include <linux/sched/signal.h>
20#include <linux/sched/debug.h>
21
22#include <trace/events/sched.h>
23
24/*
25 * The number of tasks checked:
26 */
27int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
28
29/*
30 * Limit number of tasks checked in a batch.
31 *
32 * This value controls the preemptibility of khungtaskd since preemption
33 * is disabled during the critical section. It also controls the size of
34 * the RCU grace period. So it needs to be upper-bound.
35 */
36#define HUNG_TASK_BATCHING 1024
37
38/*
39 * Zero means infinite timeout - no checking done:
40 */
41unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
42
43int __read_mostly sysctl_hung_task_warnings = 10;
44
45static int __read_mostly did_panic;
46static bool hung_task_show_lock;
47static bool hung_task_call_panic;
48
49static struct task_struct *watchdog_task;
50
51/*
52 * Should we panic (and reboot, if panic_timeout= is set) when a
53 * hung task is detected:
54 */
55unsigned int __read_mostly sysctl_hung_task_panic =
56 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
57
58static int __init hung_task_panic_setup(char *str)
59{
60 int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
61
62 if (rc)
63 return rc;
64 return 1;
65}
66__setup("hung_task_panic=", hung_task_panic_setup);
67
68static int
69hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
70{
71 did_panic = 1;
72
73 return NOTIFY_DONE;
74}
75
76static struct notifier_block panic_block = {
77 .notifier_call = hung_task_panic,
78};
79
80static void check_hung_task(struct task_struct *t, unsigned long timeout)
81{
82 unsigned long switch_count = t->nvcsw + t->nivcsw;
83
84 /*
85 * Ensure the task is not frozen.
86 * Also, skip vfork and any other user process that freezer should skip.
87 */
88 if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
89 return;
90
91 /*
92 * When a freshly created task is scheduled once, changes its state to
93 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
94 * musn't be checked.
95 */
96 if (unlikely(!switch_count))
97 return;
98
99 if (switch_count != t->last_switch_count) {
100 t->last_switch_count = switch_count;
101 return;
102 }
103
104 trace_sched_process_hang(t);
105
106 if (!sysctl_hung_task_warnings && !sysctl_hung_task_panic)
107 return;
108
109 /*
110 * Ok, the task did not get scheduled for more than 2 minutes,
111 * complain:
112 */
113 if (sysctl_hung_task_warnings) {
114 if (sysctl_hung_task_warnings > 0)
115 sysctl_hung_task_warnings--;
116 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
117 t->comm, t->pid, timeout);
118 pr_err(" %s %s %.*s\n",
119 print_tainted(), init_utsname()->release,
120 (int)strcspn(init_utsname()->version, " "),
121 init_utsname()->version);
122 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
123 " disables this message.\n");
124 sched_show_task(t);
125 hung_task_show_lock = true;
126 }
127
128 touch_nmi_watchdog();
129
130 if (sysctl_hung_task_panic) {
131 hung_task_show_lock = true;
132 hung_task_call_panic = true;
133 }
134}
135
136/*
137 * To avoid extending the RCU grace period for an unbounded amount of time,
138 * periodically exit the critical section and enter a new one.
139 *
140 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
141 * to exit the grace period. For classic RCU, a reschedule is required.
142 */
143static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
144{
145 bool can_cont;
146
147 get_task_struct(g);
148 get_task_struct(t);
149 rcu_read_unlock();
150 cond_resched();
151 rcu_read_lock();
152 can_cont = pid_alive(g) && pid_alive(t);
153 put_task_struct(t);
154 put_task_struct(g);
155
156 return can_cont;
157}
158
159/*
160 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
161 * a really long time (120 seconds). If that happens, print out
162 * a warning.
163 */
164static void check_hung_uninterruptible_tasks(unsigned long timeout)
165{
166 int max_count = sysctl_hung_task_check_count;
167 int batch_count = HUNG_TASK_BATCHING;
168 struct task_struct *g, *t;
169
170 /*
171 * If the system crashed already then all bets are off,
172 * do not report extra hung tasks:
173 */
174 if (test_taint(TAINT_DIE) || did_panic)
175 return;
176
177 hung_task_show_lock = false;
178 rcu_read_lock();
179 for_each_process_thread(g, t) {
180 if (!max_count--)
181 goto unlock;
182 if (!--batch_count) {
183 batch_count = HUNG_TASK_BATCHING;
184 if (!rcu_lock_break(g, t))
185 goto unlock;
186 }
187 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
188 if (t->state == TASK_UNINTERRUPTIBLE)
189 check_hung_task(t, timeout);
190 }
191 unlock:
192 rcu_read_unlock();
193 if (hung_task_show_lock)
194 debug_show_all_locks();
195 if (hung_task_call_panic) {
196 trigger_all_cpu_backtrace();
197 panic("hung_task: blocked tasks");
198 }
199}
200
201static long hung_timeout_jiffies(unsigned long last_checked,
202 unsigned long timeout)
203{
204 /* timeout of 0 will disable the watchdog */
205 return timeout ? last_checked - jiffies + timeout * HZ :
206 MAX_SCHEDULE_TIMEOUT;
207}
208
209/*
210 * Process updating of timeout sysctl
211 */
212int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
213 void __user *buffer,
214 size_t *lenp, loff_t *ppos)
215{
216 int ret;
217
218 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
219
220 if (ret || !write)
221 goto out;
222
223 wake_up_process(watchdog_task);
224
225 out:
226 return ret;
227}
228
229static atomic_t reset_hung_task = ATOMIC_INIT(0);
230
231void reset_hung_task_detector(void)
232{
233 atomic_set(&reset_hung_task, 1);
234}
235EXPORT_SYMBOL_GPL(reset_hung_task_detector);
236
237/*
238 * kthread which checks for tasks stuck in D state
239 */
240static int watchdog(void *dummy)
241{
242 unsigned long hung_last_checked = jiffies;
243
244 set_user_nice(current, 0);
245
246 for ( ; ; ) {
247 unsigned long timeout = sysctl_hung_task_timeout_secs;
248 long t = hung_timeout_jiffies(hung_last_checked, timeout);
249
250 if (t <= 0) {
251 if (!atomic_xchg(&reset_hung_task, 0))
252 check_hung_uninterruptible_tasks(timeout);
253 hung_last_checked = jiffies;
254 continue;
255 }
256 schedule_timeout_interruptible(t);
257 }
258
259 return 0;
260}
261
262static int __init hung_task_init(void)
263{
264 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
265 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
266
267 return 0;
268}
269subsys_initcall(hung_task_init);
270