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