projects/linux·blob v4.20 · refs

310 lines · 7.2 KiB

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/suspend.h>
19#include <linux/utsname.h>
20#include <linux/sched/signal.h>
21#include <linux/sched/debug.h>
22
23#include <trace/events/sched.h>
24
25/*
26 * The number of tasks checked:
27 */
28int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
29
30/*
31 * Limit number of tasks checked in a batch.
32 *
33 * This value controls the preemptibility of khungtaskd since preemption
34 * is disabled during the critical section. It also controls the size of
35 * the RCU grace period. So it needs to be upper-bound.
36 */
37#define HUNG_TASK_BATCHING 1024
38
39/*
40 * Zero means infinite timeout - no checking done:
41 */
42unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
43
44/*
45 * Zero (default value) means use sysctl_hung_task_timeout_secs:
46 */
47unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
48
49int __read_mostly sysctl_hung_task_warnings = 10;
50
51static int __read_mostly did_panic;
52static bool hung_task_show_lock;
53static bool hung_task_call_panic;
54
55static struct task_struct *watchdog_task;
56
57/*
58 * Should we panic (and reboot, if panic_timeout= is set) when a
59 * hung task is detected:
60 */
61unsigned int __read_mostly sysctl_hung_task_panic =
62 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
63
64static int __init hung_task_panic_setup(char *str)
65{
66 int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
67
68 if (rc)
69 return rc;
70 return 1;
71}
72__setup("hung_task_panic=", hung_task_panic_setup);
73
74static int
75hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
76{
77 did_panic = 1;
78
79 return NOTIFY_DONE;
80}
81
82static struct notifier_block panic_block = {
83 .notifier_call = hung_task_panic,
84};
85
86static void check_hung_task(struct task_struct *t, unsigned long timeout)
87{
88 unsigned long switch_count = t->nvcsw + t->nivcsw;
89
90 /*
91 * Ensure the task is not frozen.
92 * Also, skip vfork and any other user process that freezer should skip.
93 */
94 if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
95 return;
96
97 /*
98 * When a freshly created task is scheduled once, changes its state to
99 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
100 * musn't be checked.
101 */
102 if (unlikely(!switch_count))
103 return;
104
105 if (switch_count != t->last_switch_count) {
106 t->last_switch_count = switch_count;
107 t->last_switch_time = jiffies;
108 return;
109 }
110 if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
111 return;
112
113 trace_sched_process_hang(t);
114
115 if (!sysctl_hung_task_warnings && !sysctl_hung_task_panic)
116 return;
117
118 /*
119 * Ok, the task did not get scheduled for more than 2 minutes,
120 * complain:
121 */
122 if (sysctl_hung_task_warnings) {
123 if (sysctl_hung_task_warnings > 0)
124 sysctl_hung_task_warnings--;
125 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
126 t->comm, t->pid, timeout);
127 pr_err(" %s %s %.*s\n",
128 print_tainted(), init_utsname()->release,
129 (int)strcspn(init_utsname()->version, " "),
130 init_utsname()->version);
131 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
132 " disables this message.\n");
133 sched_show_task(t);
134 hung_task_show_lock = true;
135 }
136
137 touch_nmi_watchdog();
138
139 if (sysctl_hung_task_panic) {
140 hung_task_show_lock = true;
141 hung_task_call_panic = true;
142 }
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 */
152static 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 */
173static void check_hung_uninterruptible_tasks(unsigned long timeout)
174{
175 int max_count = sysctl_hung_task_check_count;
176 int batch_count = HUNG_TASK_BATCHING;
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 (!--batch_count) {
192 batch_count = HUNG_TASK_BATCHING;
193 if (!rcu_lock_break(g, t))
194 goto unlock;
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
210static 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 */
221int 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
238static atomic_t reset_hung_task = ATOMIC_INIT(0);
239
240void reset_hung_task_detector(void)
241{
242 atomic_set(&reset_hung_task, 1);
243}
244EXPORT_SYMBOL_GPL(reset_hung_task_detector);
245
246static bool hung_detector_suspended;
247
248static 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 */
271static 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
299static 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}
310subsys_initcall(hung_task_init);