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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/module.h> |
17 | #include <linux/sysctl.h> |
18 | |
19 | /* |
20 | * The number of tasks checked: |
21 | */ |
22 | unsigned long __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT; |
23 | |
24 | /* |
25 | * Limit number of tasks checked in a batch. |
26 | * |
27 | * This value controls the preemptibility of khungtaskd since preemption |
28 | * is disabled during the critical section. It also controls the size of |
29 | * the RCU grace period. So it needs to be upper-bound. |
30 | */ |
31 | #define HUNG_TASK_BATCHING 1024 |
32 | |
33 | /* |
34 | * Zero means infinite timeout - no checking done: |
35 | */ |
36 | unsigned long __read_mostly sysctl_hung_task_timeout_secs = 120; |
37 | |
38 | unsigned long __read_mostly sysctl_hung_task_warnings = 10; |
39 | |
40 | static int __read_mostly did_panic; |
41 | |
42 | static struct task_struct *watchdog_task; |
43 | |
44 | /* |
45 | * Should we panic (and reboot, if panic_timeout= is set) when a |
46 | * hung task is detected: |
47 | */ |
48 | unsigned int __read_mostly sysctl_hung_task_panic = |
49 | CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE; |
50 | |
51 | static int __init hung_task_panic_setup(char *str) |
52 | { |
53 | sysctl_hung_task_panic = simple_strtoul(str, NULL, 0); |
54 | |
55 | return 1; |
56 | } |
57 | __setup("hung_task_panic=", hung_task_panic_setup); |
58 | |
59 | static int |
60 | hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr) |
61 | { |
62 | did_panic = 1; |
63 | |
64 | return NOTIFY_DONE; |
65 | } |
66 | |
67 | static struct notifier_block panic_block = { |
68 | .notifier_call = hung_task_panic, |
69 | }; |
70 | |
71 | static void check_hung_task(struct task_struct *t, unsigned long timeout) |
72 | { |
73 | unsigned long switch_count = t->nvcsw + t->nivcsw; |
74 | |
75 | /* |
76 | * Ensure the task is not frozen. |
77 | * Also, when a freshly created task is scheduled once, changes |
78 | * its state to TASK_UNINTERRUPTIBLE without having ever been |
79 | * switched out once, it musn't be checked. |
80 | */ |
81 | if (unlikely(t->flags & PF_FROZEN || !switch_count)) |
82 | return; |
83 | |
84 | if (switch_count != t->last_switch_count) { |
85 | t->last_switch_count = switch_count; |
86 | return; |
87 | } |
88 | if (!sysctl_hung_task_warnings) |
89 | return; |
90 | sysctl_hung_task_warnings--; |
91 | |
92 | /* |
93 | * Ok, the task did not get scheduled for more than 2 minutes, |
94 | * complain: |
95 | */ |
96 | printk(KERN_ERR "INFO: task %s:%d blocked for more than " |
97 | "%ld seconds.\n", t->comm, t->pid, timeout); |
98 | printk(KERN_ERR "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\"" |
99 | " disables this message.\n"); |
100 | sched_show_task(t); |
101 | debug_show_held_locks(t); |
102 | |
103 | touch_nmi_watchdog(); |
104 | |
105 | if (sysctl_hung_task_panic) |
106 | panic("hung_task: blocked tasks"); |
107 | } |
108 | |
109 | /* |
110 | * To avoid extending the RCU grace period for an unbounded amount of time, |
111 | * periodically exit the critical section and enter a new one. |
112 | * |
113 | * For preemptible RCU it is sufficient to call rcu_read_unlock in order |
114 | * to exit the grace period. For classic RCU, a reschedule is required. |
115 | */ |
116 | static void rcu_lock_break(struct task_struct *g, struct task_struct *t) |
117 | { |
118 | get_task_struct(g); |
119 | get_task_struct(t); |
120 | rcu_read_unlock(); |
121 | cond_resched(); |
122 | rcu_read_lock(); |
123 | put_task_struct(t); |
124 | put_task_struct(g); |
125 | } |
126 | |
127 | /* |
128 | * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for |
129 | * a really long time (120 seconds). If that happens, print out |
130 | * a warning. |
131 | */ |
132 | static void check_hung_uninterruptible_tasks(unsigned long timeout) |
133 | { |
134 | int max_count = sysctl_hung_task_check_count; |
135 | int batch_count = HUNG_TASK_BATCHING; |
136 | struct task_struct *g, *t; |
137 | |
138 | /* |
139 | * If the system crashed already then all bets are off, |
140 | * do not report extra hung tasks: |
141 | */ |
142 | if (test_taint(TAINT_DIE) || did_panic) |
143 | return; |
144 | |
145 | rcu_read_lock(); |
146 | do_each_thread(g, t) { |
147 | if (!max_count--) |
148 | goto unlock; |
149 | if (!--batch_count) { |
150 | batch_count = HUNG_TASK_BATCHING; |
151 | rcu_lock_break(g, t); |
152 | /* Exit if t or g was unhashed during refresh. */ |
153 | if (t->state == TASK_DEAD || g->state == TASK_DEAD) |
154 | goto unlock; |
155 | } |
156 | /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */ |
157 | if (t->state == TASK_UNINTERRUPTIBLE) |
158 | check_hung_task(t, timeout); |
159 | } while_each_thread(g, t); |
160 | unlock: |
161 | rcu_read_unlock(); |
162 | } |
163 | |
164 | static unsigned long timeout_jiffies(unsigned long timeout) |
165 | { |
166 | /* timeout of 0 will disable the watchdog */ |
167 | return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT; |
168 | } |
169 | |
170 | /* |
171 | * Process updating of timeout sysctl |
172 | */ |
173 | int proc_dohung_task_timeout_secs(struct ctl_table *table, int write, |
174 | void __user *buffer, |
175 | size_t *lenp, loff_t *ppos) |
176 | { |
177 | int ret; |
178 | |
179 | ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); |
180 | |
181 | if (ret || !write) |
182 | goto out; |
183 | |
184 | wake_up_process(watchdog_task); |
185 | |
186 | out: |
187 | return ret; |
188 | } |
189 | |
190 | /* |
191 | * kthread which checks for tasks stuck in D state |
192 | */ |
193 | static int watchdog(void *dummy) |
194 | { |
195 | set_user_nice(current, 0); |
196 | |
197 | for ( ; ; ) { |
198 | unsigned long timeout = sysctl_hung_task_timeout_secs; |
199 | |
200 | while (schedule_timeout_interruptible(timeout_jiffies(timeout))) |
201 | timeout = sysctl_hung_task_timeout_secs; |
202 | |
203 | check_hung_uninterruptible_tasks(timeout); |
204 | } |
205 | |
206 | return 0; |
207 | } |
208 | |
209 | static int __init hung_task_init(void) |
210 | { |
211 | atomic_notifier_chain_register(&panic_notifier_list, &panic_block); |
212 | watchdog_task = kthread_run(watchdog, NULL, "khungtaskd"); |
213 | |
214 | return 0; |
215 | } |
216 | |
217 | module_init(hung_task_init); |
218 |
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