projects/linux·blob v5.19-rc2 · refs

400 lines · 9.6 KiB

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/panic_notifier.h>
19#include <linux/sysctl.h>
20#include <linux/suspend.h>
21#include <linux/utsname.h>
22#include <linux/sched/signal.h>
23#include <linux/sched/debug.h>
24#include <linux/sched/sysctl.h>
25
26#include <trace/events/sched.h>
27
28/*
29 * The number of tasks checked:
30 */
31int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
32
33/*
34 * Limit number of tasks checked in a batch.
35 *
36 * This value controls the preemptibility of khungtaskd since preemption
37 * is disabled during the critical section. It also controls the size of
38 * the RCU grace period. So it needs to be upper-bound.
39 */
40#define HUNG_TASK_LOCK_BREAK (HZ / 10)
41
42/*
43 * Zero means infinite timeout - no checking done:
44 */
45unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
46
47/*
48 * Zero (default value) means use sysctl_hung_task_timeout_secs:
49 */
50unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
51
52int __read_mostly sysctl_hung_task_warnings = 10;
53
54static int __read_mostly did_panic;
55static bool hung_task_show_lock;
56static bool hung_task_call_panic;
57static bool hung_task_show_all_bt;
58
59static struct task_struct *watchdog_task;
60
61#ifdef CONFIG_SMP
62/*
63 * Should we dump all CPUs backtraces in a hung task event?
64 * Defaults to 0, can be changed via sysctl.
65 */
66static unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace;
67#else
68#define sysctl_hung_task_all_cpu_backtrace 0
69#endif /* CONFIG_SMP */
70
71/*
72 * Should we panic (and reboot, if panic_timeout= is set) when a
73 * hung task is detected:
74 */
75unsigned int __read_mostly sysctl_hung_task_panic =
76 IS_ENABLED(CONFIG_BOOTPARAM_HUNG_TASK_PANIC);
77
78static int
79hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
80{
81 did_panic = 1;
82
83 return NOTIFY_DONE;
84}
85
86static struct notifier_block panic_block = {
87 .notifier_call = hung_task_panic,
88};
89
90static void check_hung_task(struct task_struct *t, unsigned long timeout)
91{
92 unsigned long switch_count = t->nvcsw + t->nivcsw;
93
94 /*
95 * Ensure the task is not frozen.
96 * Also, skip vfork and any other user process that freezer should skip.
97 */
98 if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
99 return;
100
101 /*
102 * When a freshly created task is scheduled once, changes its state to
103 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
104 * musn't be checked.
105 */
106 if (unlikely(!switch_count))
107 return;
108
109 if (switch_count != t->last_switch_count) {
110 t->last_switch_count = switch_count;
111 t->last_switch_time = jiffies;
112 return;
113 }
114 if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
115 return;
116
117 trace_sched_process_hang(t);
118
119 if (sysctl_hung_task_panic) {
120 console_verbose();
121 hung_task_show_lock = true;
122 hung_task_call_panic = true;
123 }
124
125 /*
126 * Ok, the task did not get scheduled for more than 2 minutes,
127 * complain:
128 */
129 if (sysctl_hung_task_warnings) {
130 printk_prefer_direct_enter();
131
132 if (sysctl_hung_task_warnings > 0)
133 sysctl_hung_task_warnings--;
134 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
135 t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
136 pr_err(" %s %s %.*s\n",
137 print_tainted(), init_utsname()->release,
138 (int)strcspn(init_utsname()->version, " "),
139 init_utsname()->version);
140 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
141 " disables this message.\n");
142 sched_show_task(t);
143 hung_task_show_lock = true;
144
145 if (sysctl_hung_task_all_cpu_backtrace)
146 hung_task_show_all_bt = true;
147
148 printk_prefer_direct_exit();
149 }
150
151 touch_nmi_watchdog();
152}
153
154/*
155 * To avoid extending the RCU grace period for an unbounded amount of time,
156 * periodically exit the critical section and enter a new one.
157 *
158 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
159 * to exit the grace period. For classic RCU, a reschedule is required.
160 */
161static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
162{
163 bool can_cont;
164
165 get_task_struct(g);
166 get_task_struct(t);
167 rcu_read_unlock();
168 cond_resched();
169 rcu_read_lock();
170 can_cont = pid_alive(g) && pid_alive(t);
171 put_task_struct(t);
172 put_task_struct(g);
173
174 return can_cont;
175}
176
177/*
178 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
179 * a really long time (120 seconds). If that happens, print out
180 * a warning.
181 */
182static void check_hung_uninterruptible_tasks(unsigned long timeout)
183{
184 int max_count = sysctl_hung_task_check_count;
185 unsigned long last_break = jiffies;
186 struct task_struct *g, *t;
187
188 /*
189 * If the system crashed already then all bets are off,
190 * do not report extra hung tasks:
191 */
192 if (test_taint(TAINT_DIE) || did_panic)
193 return;
194
195 hung_task_show_lock = false;
196 rcu_read_lock();
197 for_each_process_thread(g, t) {
198 if (!max_count--)
199 goto unlock;
200 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
201 if (!rcu_lock_break(g, t))
202 goto unlock;
203 last_break = jiffies;
204 }
205 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
206 if (READ_ONCE(t->__state) == TASK_UNINTERRUPTIBLE)
207 check_hung_task(t, timeout);
208 }
209 unlock:
210 rcu_read_unlock();
211 if (hung_task_show_lock) {
212 printk_prefer_direct_enter();
213 debug_show_all_locks();
214 printk_prefer_direct_exit();
215 }
216
217 if (hung_task_show_all_bt) {
218 hung_task_show_all_bt = false;
219 printk_prefer_direct_enter();
220 trigger_all_cpu_backtrace();
221 printk_prefer_direct_exit();
222 }
223
224 if (hung_task_call_panic)
225 panic("hung_task: blocked tasks");
226}
227
228static long hung_timeout_jiffies(unsigned long last_checked,
229 unsigned long timeout)
230{
231 /* timeout of 0 will disable the watchdog */
232 return timeout ? last_checked - jiffies + timeout * HZ :
233 MAX_SCHEDULE_TIMEOUT;
234}
235
236#ifdef CONFIG_SYSCTL
237/*
238 * Process updating of timeout sysctl
239 */
240static int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
241 void __user *buffer,
242 size_t *lenp, loff_t *ppos)
243{
244 int ret;
245
246 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
247
248 if (ret || !write)
249 goto out;
250
251 wake_up_process(watchdog_task);
252
253 out:
254 return ret;
255}
256
257/*
258 * This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs
259 * and hung_task_check_interval_secs
260 */
261static const unsigned long hung_task_timeout_max = (LONG_MAX / HZ);
262static struct ctl_table hung_task_sysctls[] = {
263#ifdef CONFIG_SMP
264 {
265 .procname = "hung_task_all_cpu_backtrace",
266 .data = &sysctl_hung_task_all_cpu_backtrace,
267 .maxlen = sizeof(int),
268 .mode = 0644,
269 .proc_handler = proc_dointvec_minmax,
270 .extra1 = SYSCTL_ZERO,
271 .extra2 = SYSCTL_ONE,
272 },
273#endif /* CONFIG_SMP */
274 {
275 .procname = "hung_task_panic",
276 .data = &sysctl_hung_task_panic,
277 .maxlen = sizeof(int),
278 .mode = 0644,
279 .proc_handler = proc_dointvec_minmax,
280 .extra1 = SYSCTL_ZERO,
281 .extra2 = SYSCTL_ONE,
282 },
283 {
284 .procname = "hung_task_check_count",
285 .data = &sysctl_hung_task_check_count,
286 .maxlen = sizeof(int),
287 .mode = 0644,
288 .proc_handler = proc_dointvec_minmax,
289 .extra1 = SYSCTL_ZERO,
290 },
291 {
292 .procname = "hung_task_timeout_secs",
293 .data = &sysctl_hung_task_timeout_secs,
294 .maxlen = sizeof(unsigned long),
295 .mode = 0644,
296 .proc_handler = proc_dohung_task_timeout_secs,
297 .extra2 = (void *)&hung_task_timeout_max,
298 },
299 {
300 .procname = "hung_task_check_interval_secs",
301 .data = &sysctl_hung_task_check_interval_secs,
302 .maxlen = sizeof(unsigned long),
303 .mode = 0644,
304 .proc_handler = proc_dohung_task_timeout_secs,
305 .extra2 = (void *)&hung_task_timeout_max,
306 },
307 {
308 .procname = "hung_task_warnings",
309 .data = &sysctl_hung_task_warnings,
310 .maxlen = sizeof(int),
311 .mode = 0644,
312 .proc_handler = proc_dointvec_minmax,
313 .extra1 = SYSCTL_NEG_ONE,
314 },
315 {}
316};
317
318static void __init hung_task_sysctl_init(void)
319{
320 register_sysctl_init("kernel", hung_task_sysctls);
321}
322#else
323#define hung_task_sysctl_init() do { } while (0)
324#endif /* CONFIG_SYSCTL */
325
326
327static atomic_t reset_hung_task = ATOMIC_INIT(0);
328
329void reset_hung_task_detector(void)
330{
331 atomic_set(&reset_hung_task, 1);
332}
333EXPORT_SYMBOL_GPL(reset_hung_task_detector);
334
335static bool hung_detector_suspended;
336
337static int hungtask_pm_notify(struct notifier_block *self,
338 unsigned long action, void *hcpu)
339{
340 switch (action) {
341 case PM_SUSPEND_PREPARE:
342 case PM_HIBERNATION_PREPARE:
343 case PM_RESTORE_PREPARE:
344 hung_detector_suspended = true;
345 break;
346 case PM_POST_SUSPEND:
347 case PM_POST_HIBERNATION:
348 case PM_POST_RESTORE:
349 hung_detector_suspended = false;
350 break;
351 default:
352 break;
353 }
354 return NOTIFY_OK;
355}
356
357/*
358 * kthread which checks for tasks stuck in D state
359 */
360static int watchdog(void *dummy)
361{
362 unsigned long hung_last_checked = jiffies;
363
364 set_user_nice(current, 0);
365
366 for ( ; ; ) {
367 unsigned long timeout = sysctl_hung_task_timeout_secs;
368 unsigned long interval = sysctl_hung_task_check_interval_secs;
369 long t;
370
371 if (interval == 0)
372 interval = timeout;
373 interval = min_t(unsigned long, interval, timeout);
374 t = hung_timeout_jiffies(hung_last_checked, interval);
375 if (t <= 0) {
376 if (!atomic_xchg(&reset_hung_task, 0) &&
377 !hung_detector_suspended)
378 check_hung_uninterruptible_tasks(timeout);
379 hung_last_checked = jiffies;
380 continue;
381 }
382 schedule_timeout_interruptible(t);
383 }
384
385 return 0;
386}
387
388static int __init hung_task_init(void)
389{
390 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
391
392 /* Disable hung task detector on suspend */
393 pm_notifier(hungtask_pm_notify, 0);
394
395 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
396 hung_task_sysctl_init();
397
398 return 0;
399}
400subsys_initcall(hung_task_init);