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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 | */ | |
27 | int __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 | */ | |
41 | unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT; | |
42 | ||
43 | int __read_mostly sysctl_hung_task_warnings = 10; | |
44 | ||
45 | static int __read_mostly did_panic; | |
46 | static bool hung_task_show_lock; | |
47 | ||
48 | static struct task_struct *watchdog_task; | |
49 | ||
50 | /* | |
51 | * Should we panic (and reboot, if panic_timeout= is set) when a | |
52 | * hung task is detected: | |
53 | */ | |
54 | unsigned int __read_mostly sysctl_hung_task_panic = | |
55 | CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE; | |
56 | ||
57 | static int __init hung_task_panic_setup(char *str) | |
58 | { | |
59 | int rc = kstrtouint(str, 0, &sysctl_hung_task_panic); | |
60 | ||
61 | if (rc) | |
62 | return rc; | |
63 | return 1; | |
64 | } | |
65 | __setup("hung_task_panic=", hung_task_panic_setup); | |
66 | ||
67 | static int | |
68 | hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr) | |
69 | { | |
70 | did_panic = 1; | |
71 | ||
72 | return NOTIFY_DONE; | |
73 | } | |
74 | ||
75 | static struct notifier_block panic_block = { | |
76 | .notifier_call = hung_task_panic, | |
77 | }; | |
78 | ||
79 | static void check_hung_task(struct task_struct *t, unsigned long timeout) | |
80 | { | |
81 | unsigned long switch_count = t->nvcsw + t->nivcsw; | |
82 | ||
83 | /* | |
84 | * Ensure the task is not frozen. | |
85 | * Also, skip vfork and any other user process that freezer should skip. | |
86 | */ | |
87 | if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP))) | |
88 | return; | |
89 | ||
90 | /* | |
91 | * When a freshly created task is scheduled once, changes its state to | |
92 | * TASK_UNINTERRUPTIBLE without having ever been switched out once, it | |
93 | * musn't be checked. | |
94 | */ | |
95 | if (unlikely(!switch_count)) | |
96 | return; | |
97 | ||
98 | if (switch_count != t->last_switch_count) { | |
99 | t->last_switch_count = switch_count; | |
100 | return; | |
101 | } | |
102 | ||
103 | trace_sched_process_hang(t); | |
104 | ||
105 | if (!sysctl_hung_task_warnings && !sysctl_hung_task_panic) | |
106 | return; | |
107 | ||
108 | /* | |
109 | * Ok, the task did not get scheduled for more than 2 minutes, | |
110 | * complain: | |
111 | */ | |
112 | if (sysctl_hung_task_warnings) { | |
113 | if (sysctl_hung_task_warnings > 0) | |
114 | sysctl_hung_task_warnings--; | |
115 | pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n", | |
116 | t->comm, t->pid, timeout); | |
117 | pr_err(" %s %s %.*s\n", | |
118 | print_tainted(), init_utsname()->release, | |
119 | (int)strcspn(init_utsname()->version, " "), | |
120 | init_utsname()->version); | |
121 | pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\"" | |
122 | " disables this message.\n"); | |
123 | sched_show_task(t); | |
124 | hung_task_show_lock = true; | |
125 | } | |
126 | ||
127 | touch_nmi_watchdog(); | |
128 | ||
129 | if (sysctl_hung_task_panic) { | |
130 | if (hung_task_show_lock) | |
131 | debug_show_all_locks(); | |
132 | trigger_all_cpu_backtrace(); | |
133 | panic("hung_task: blocked tasks"); | |
134 | } | |
135 | } | |
136 | ||
137 | /* | |
138 | * To avoid extending the RCU grace period for an unbounded amount of time, | |
139 | * periodically exit the critical section and enter a new one. | |
140 | * | |
141 | * For preemptible RCU it is sufficient to call rcu_read_unlock in order | |
142 | * to exit the grace period. For classic RCU, a reschedule is required. | |
143 | */ | |
144 | static bool rcu_lock_break(struct task_struct *g, struct task_struct *t) | |
145 | { | |
146 | bool can_cont; | |
147 | ||
148 | get_task_struct(g); | |
149 | get_task_struct(t); | |
150 | rcu_read_unlock(); | |
151 | cond_resched(); | |
152 | rcu_read_lock(); | |
153 | can_cont = pid_alive(g) && pid_alive(t); | |
154 | put_task_struct(t); | |
155 | put_task_struct(g); | |
156 | ||
157 | return can_cont; | |
158 | } | |
159 | ||
160 | /* | |
161 | * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for | |
162 | * a really long time (120 seconds). If that happens, print out | |
163 | * a warning. | |
164 | */ | |
165 | static void check_hung_uninterruptible_tasks(unsigned long timeout) | |
166 | { | |
167 | int max_count = sysctl_hung_task_check_count; | |
168 | int batch_count = HUNG_TASK_BATCHING; | |
169 | struct task_struct *g, *t; | |
170 | ||
171 | /* | |
172 | * If the system crashed already then all bets are off, | |
173 | * do not report extra hung tasks: | |
174 | */ | |
175 | if (test_taint(TAINT_DIE) || did_panic) | |
176 | return; | |
177 | ||
178 | hung_task_show_lock = false; | |
179 | rcu_read_lock(); | |
180 | for_each_process_thread(g, t) { | |
181 | if (!max_count--) | |
182 | goto unlock; | |
183 | if (!--batch_count) { | |
184 | batch_count = HUNG_TASK_BATCHING; | |
185 | if (!rcu_lock_break(g, t)) | |
186 | goto unlock; | |
187 | } | |
188 | /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */ | |
189 | if (t->state == TASK_UNINTERRUPTIBLE) | |
190 | check_hung_task(t, timeout); | |
191 | } | |
192 | unlock: | |
193 | rcu_read_unlock(); | |
194 | if (hung_task_show_lock) | |
195 | debug_show_all_locks(); | |
196 | } | |
197 | ||
198 | static long hung_timeout_jiffies(unsigned long last_checked, | |
199 | unsigned long timeout) | |
200 | { | |
201 | /* timeout of 0 will disable the watchdog */ | |
202 | return timeout ? last_checked - jiffies + timeout * HZ : | |
203 | MAX_SCHEDULE_TIMEOUT; | |
204 | } | |
205 | ||
206 | /* | |
207 | * Process updating of timeout sysctl | |
208 | */ | |
209 | int proc_dohung_task_timeout_secs(struct ctl_table *table, int write, | |
210 | void __user *buffer, | |
211 | size_t *lenp, loff_t *ppos) | |
212 | { | |
213 | int ret; | |
214 | ||
215 | ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); | |
216 | ||
217 | if (ret || !write) | |
218 | goto out; | |
219 | ||
220 | wake_up_process(watchdog_task); | |
221 | ||
222 | out: | |
223 | return ret; | |
224 | } | |
225 | ||
226 | static atomic_t reset_hung_task = ATOMIC_INIT(0); | |
227 | ||
228 | void reset_hung_task_detector(void) | |
229 | { | |
230 | atomic_set(&reset_hung_task, 1); | |
231 | } | |
232 | EXPORT_SYMBOL_GPL(reset_hung_task_detector); | |
233 | ||
234 | /* | |
235 | * kthread which checks for tasks stuck in D state | |
236 | */ | |
237 | static int watchdog(void *dummy) | |
238 | { | |
239 | unsigned long hung_last_checked = jiffies; | |
240 | ||
241 | set_user_nice(current, 0); | |
242 | ||
243 | for ( ; ; ) { | |
244 | unsigned long timeout = sysctl_hung_task_timeout_secs; | |
245 | long t = hung_timeout_jiffies(hung_last_checked, timeout); | |
246 | ||
247 | if (t <= 0) { | |
248 | if (!atomic_xchg(&reset_hung_task, 0)) | |
249 | check_hung_uninterruptible_tasks(timeout); | |
250 | hung_last_checked = jiffies; | |
251 | continue; | |
252 | } | |
253 | schedule_timeout_interruptible(t); | |
254 | } | |
255 | ||
256 | return 0; | |
257 | } | |
258 | ||
259 | static int __init hung_task_init(void) | |
260 | { | |
261 | atomic_notifier_chain_register(&panic_notifier_list, &panic_block); | |
262 | watchdog_task = kthread_run(watchdog, NULL, "khungtaskd"); | |
263 | ||
264 | return 0; | |
265 | } | |
266 | subsys_initcall(hung_task_init); |