projects/linux·blob v5.19-rc8 · refs

391 lines · 9.4 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 if (sysctl_hung_task_warnings > 0)
131 sysctl_hung_task_warnings--;
132 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
133 t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
134 pr_err(" %s %s %.*s\n",
135 print_tainted(), init_utsname()->release,
136 (int)strcspn(init_utsname()->version, " "),
137 init_utsname()->version);
138 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
139 " disables this message.\n");
140 sched_show_task(t);
141 hung_task_show_lock = true;
142
143 if (sysctl_hung_task_all_cpu_backtrace)
144 hung_task_show_all_bt = true;
145 }
146
147 touch_nmi_watchdog();
148}
149
150/*
151 * To avoid extending the RCU grace period for an unbounded amount of time,
152 * periodically exit the critical section and enter a new one.
153 *
154 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
155 * to exit the grace period. For classic RCU, a reschedule is required.
156 */
157static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
158{
159 bool can_cont;
160
161 get_task_struct(g);
162 get_task_struct(t);
163 rcu_read_unlock();
164 cond_resched();
165 rcu_read_lock();
166 can_cont = pid_alive(g) && pid_alive(t);
167 put_task_struct(t);
168 put_task_struct(g);
169
170 return can_cont;
171}
172
173/*
174 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
175 * a really long time (120 seconds). If that happens, print out
176 * a warning.
177 */
178static void check_hung_uninterruptible_tasks(unsigned long timeout)
179{
180 int max_count = sysctl_hung_task_check_count;
181 unsigned long last_break = jiffies;
182 struct task_struct *g, *t;
183
184 /*
185 * If the system crashed already then all bets are off,
186 * do not report extra hung tasks:
187 */
188 if (test_taint(TAINT_DIE) || did_panic)
189 return;
190
191 hung_task_show_lock = false;
192 rcu_read_lock();
193 for_each_process_thread(g, t) {
194 if (!max_count--)
195 goto unlock;
196 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
197 if (!rcu_lock_break(g, t))
198 goto unlock;
199 last_break = jiffies;
200 }
201 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
202 if (READ_ONCE(t->__state) == TASK_UNINTERRUPTIBLE)
203 check_hung_task(t, timeout);
204 }
205 unlock:
206 rcu_read_unlock();
207 if (hung_task_show_lock)
208 debug_show_all_locks();
209
210 if (hung_task_show_all_bt) {
211 hung_task_show_all_bt = false;
212 trigger_all_cpu_backtrace();
213 }
214
215 if (hung_task_call_panic)
216 panic("hung_task: blocked tasks");
217}
218
219static long hung_timeout_jiffies(unsigned long last_checked,
220 unsigned long timeout)
221{
222 /* timeout of 0 will disable the watchdog */
223 return timeout ? last_checked - jiffies + timeout * HZ :
224 MAX_SCHEDULE_TIMEOUT;
225}
226
227#ifdef CONFIG_SYSCTL
228/*
229 * Process updating of timeout sysctl
230 */
231static int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
232 void __user *buffer,
233 size_t *lenp, loff_t *ppos)
234{
235 int ret;
236
237 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
238
239 if (ret || !write)
240 goto out;
241
242 wake_up_process(watchdog_task);
243
244 out:
245 return ret;
246}
247
248/*
249 * This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs
250 * and hung_task_check_interval_secs
251 */
252static const unsigned long hung_task_timeout_max = (LONG_MAX / HZ);
253static struct ctl_table hung_task_sysctls[] = {
254#ifdef CONFIG_SMP
255 {
256 .procname = "hung_task_all_cpu_backtrace",
257 .data = &sysctl_hung_task_all_cpu_backtrace,
258 .maxlen = sizeof(int),
259 .mode = 0644,
260 .proc_handler = proc_dointvec_minmax,
261 .extra1 = SYSCTL_ZERO,
262 .extra2 = SYSCTL_ONE,
263 },
264#endif /* CONFIG_SMP */
265 {
266 .procname = "hung_task_panic",
267 .data = &sysctl_hung_task_panic,
268 .maxlen = sizeof(int),
269 .mode = 0644,
270 .proc_handler = proc_dointvec_minmax,
271 .extra1 = SYSCTL_ZERO,
272 .extra2 = SYSCTL_ONE,
273 },
274 {
275 .procname = "hung_task_check_count",
276 .data = &sysctl_hung_task_check_count,
277 .maxlen = sizeof(int),
278 .mode = 0644,
279 .proc_handler = proc_dointvec_minmax,
280 .extra1 = SYSCTL_ZERO,
281 },
282 {
283 .procname = "hung_task_timeout_secs",
284 .data = &sysctl_hung_task_timeout_secs,
285 .maxlen = sizeof(unsigned long),
286 .mode = 0644,
287 .proc_handler = proc_dohung_task_timeout_secs,
288 .extra2 = (void *)&hung_task_timeout_max,
289 },
290 {
291 .procname = "hung_task_check_interval_secs",
292 .data = &sysctl_hung_task_check_interval_secs,
293 .maxlen = sizeof(unsigned long),
294 .mode = 0644,
295 .proc_handler = proc_dohung_task_timeout_secs,
296 .extra2 = (void *)&hung_task_timeout_max,
297 },
298 {
299 .procname = "hung_task_warnings",
300 .data = &sysctl_hung_task_warnings,
301 .maxlen = sizeof(int),
302 .mode = 0644,
303 .proc_handler = proc_dointvec_minmax,
304 .extra1 = SYSCTL_NEG_ONE,
305 },
306 {}
307};
308
309static void __init hung_task_sysctl_init(void)
310{
311 register_sysctl_init("kernel", hung_task_sysctls);
312}
313#else
314#define hung_task_sysctl_init() do { } while (0)
315#endif /* CONFIG_SYSCTL */
316
317
318static atomic_t reset_hung_task = ATOMIC_INIT(0);
319
320void reset_hung_task_detector(void)
321{
322 atomic_set(&reset_hung_task, 1);
323}
324EXPORT_SYMBOL_GPL(reset_hung_task_detector);
325
326static bool hung_detector_suspended;
327
328static int hungtask_pm_notify(struct notifier_block *self,
329 unsigned long action, void *hcpu)
330{
331 switch (action) {
332 case PM_SUSPEND_PREPARE:
333 case PM_HIBERNATION_PREPARE:
334 case PM_RESTORE_PREPARE:
335 hung_detector_suspended = true;
336 break;
337 case PM_POST_SUSPEND:
338 case PM_POST_HIBERNATION:
339 case PM_POST_RESTORE:
340 hung_detector_suspended = false;
341 break;
342 default:
343 break;
344 }
345 return NOTIFY_OK;
346}
347
348/*
349 * kthread which checks for tasks stuck in D state
350 */
351static int watchdog(void *dummy)
352{
353 unsigned long hung_last_checked = jiffies;
354
355 set_user_nice(current, 0);
356
357 for ( ; ; ) {
358 unsigned long timeout = sysctl_hung_task_timeout_secs;
359 unsigned long interval = sysctl_hung_task_check_interval_secs;
360 long t;
361
362 if (interval == 0)
363 interval = timeout;
364 interval = min_t(unsigned long, interval, timeout);
365 t = hung_timeout_jiffies(hung_last_checked, interval);
366 if (t <= 0) {
367 if (!atomic_xchg(&reset_hung_task, 0) &&
368 !hung_detector_suspended)
369 check_hung_uninterruptible_tasks(timeout);
370 hung_last_checked = jiffies;
371 continue;
372 }
373 schedule_timeout_interruptible(t);
374 }
375
376 return 0;
377}
378
379static int __init hung_task_init(void)
380{
381 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
382
383 /* Disable hung task detector on suspend */
384 pm_notifier(hungtask_pm_notify, 0);
385
386 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
387 hung_task_sysctl_init();
388
389 return 0;
390}
391subsys_initcall(hung_task_init);