Commit | Line | Data |
---|---|---|
e162b39a MSB |
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 | /* | |
ce9dbe24 | 20 | * The number of tasks checked: |
e162b39a | 21 | */ |
ce9dbe24 MSB |
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 | |
e162b39a MSB |
32 | |
33 | /* | |
34 | * Zero means infinite timeout - no checking done: | |
35 | */ | |
36 | unsigned long __read_mostly sysctl_hung_task_timeout_secs = 120; | |
37 | static unsigned long __read_mostly hung_task_poll_jiffies; | |
38 | ||
39 | unsigned long __read_mostly sysctl_hung_task_warnings = 10; | |
40 | ||
41 | static int __read_mostly did_panic; | |
42 | ||
43 | static struct task_struct *watchdog_task; | |
44 | ||
45 | /* | |
46 | * Should we panic (and reboot, if panic_timeout= is set) when a | |
47 | * hung task is detected: | |
48 | */ | |
49 | unsigned int __read_mostly sysctl_hung_task_panic = | |
50 | CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE; | |
51 | ||
52 | static int __init hung_task_panic_setup(char *str) | |
53 | { | |
54 | sysctl_hung_task_panic = simple_strtoul(str, NULL, 0); | |
55 | ||
56 | return 1; | |
57 | } | |
58 | __setup("hung_task_panic=", hung_task_panic_setup); | |
59 | ||
60 | static int | |
61 | hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr) | |
62 | { | |
63 | did_panic = 1; | |
64 | ||
65 | return NOTIFY_DONE; | |
66 | } | |
67 | ||
68 | static struct notifier_block panic_block = { | |
69 | .notifier_call = hung_task_panic, | |
70 | }; | |
71 | ||
72 | /* | |
73 | * Returns seconds, approximately. We don't need nanosecond | |
74 | * resolution, and we don't need to waste time with a big divide when | |
75 | * 2^30ns == 1.074s. | |
76 | */ | |
77 | static unsigned long get_timestamp(void) | |
78 | { | |
79 | int this_cpu = raw_smp_processor_id(); | |
80 | ||
81 | return cpu_clock(this_cpu) >> 30LL; /* 2^30 ~= 10^9 */ | |
82 | } | |
83 | ||
603a148f MSB |
84 | static void check_hung_task(struct task_struct *t, unsigned long now, |
85 | unsigned long timeout) | |
e162b39a MSB |
86 | { |
87 | unsigned long switch_count = t->nvcsw + t->nivcsw; | |
88 | ||
89 | if (t->flags & PF_FROZEN) | |
90 | return; | |
91 | ||
92 | if (switch_count != t->last_switch_count || !t->last_switch_timestamp) { | |
93 | t->last_switch_count = switch_count; | |
94 | t->last_switch_timestamp = now; | |
95 | return; | |
96 | } | |
603a148f | 97 | if ((long)(now - t->last_switch_timestamp) < timeout) |
e162b39a MSB |
98 | return; |
99 | if (!sysctl_hung_task_warnings) | |
100 | return; | |
101 | sysctl_hung_task_warnings--; | |
102 | ||
103 | /* | |
104 | * Ok, the task did not get scheduled for more than 2 minutes, | |
105 | * complain: | |
106 | */ | |
107 | printk(KERN_ERR "INFO: task %s:%d blocked for more than " | |
603a148f | 108 | "%ld seconds.\n", t->comm, t->pid, timeout); |
e162b39a MSB |
109 | printk(KERN_ERR "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\"" |
110 | " disables this message.\n"); | |
111 | sched_show_task(t); | |
112 | __debug_show_held_locks(t); | |
113 | ||
114 | t->last_switch_timestamp = now; | |
115 | touch_nmi_watchdog(); | |
116 | ||
117 | if (sysctl_hung_task_panic) | |
118 | panic("hung_task: blocked tasks"); | |
119 | } | |
120 | ||
ce9dbe24 MSB |
121 | /* |
122 | * To avoid extending the RCU grace period for an unbounded amount of time, | |
123 | * periodically exit the critical section and enter a new one. | |
124 | * | |
125 | * For preemptible RCU it is sufficient to call rcu_read_unlock in order | |
126 | * exit the grace period. For classic RCU, a reschedule is required. | |
127 | */ | |
128 | static void rcu_lock_break(struct task_struct *g, struct task_struct *t) | |
129 | { | |
130 | get_task_struct(g); | |
131 | get_task_struct(t); | |
132 | rcu_read_unlock(); | |
133 | cond_resched(); | |
134 | rcu_read_lock(); | |
135 | put_task_struct(t); | |
136 | put_task_struct(g); | |
137 | } | |
138 | ||
e162b39a MSB |
139 | /* |
140 | * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for | |
141 | * a really long time (120 seconds). If that happens, print out | |
142 | * a warning. | |
143 | */ | |
603a148f | 144 | static void check_hung_uninterruptible_tasks(unsigned long timeout) |
e162b39a MSB |
145 | { |
146 | int max_count = sysctl_hung_task_check_count; | |
ce9dbe24 | 147 | int batch_count = HUNG_TASK_BATCHING; |
e162b39a MSB |
148 | unsigned long now = get_timestamp(); |
149 | struct task_struct *g, *t; | |
150 | ||
151 | /* | |
152 | * If the system crashed already then all bets are off, | |
153 | * do not report extra hung tasks: | |
154 | */ | |
155 | if (test_taint(TAINT_DIE) || did_panic) | |
156 | return; | |
157 | ||
94be52dc | 158 | rcu_read_lock(); |
e162b39a MSB |
159 | do_each_thread(g, t) { |
160 | if (!--max_count) | |
161 | goto unlock; | |
ce9dbe24 MSB |
162 | if (!--batch_count) { |
163 | batch_count = HUNG_TASK_BATCHING; | |
164 | rcu_lock_break(g, t); | |
165 | /* Exit if t or g was unhashed during refresh. */ | |
166 | if (t->state == TASK_DEAD || g->state == TASK_DEAD) | |
167 | goto unlock; | |
168 | } | |
e162b39a MSB |
169 | /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */ |
170 | if (t->state == TASK_UNINTERRUPTIBLE) | |
603a148f | 171 | check_hung_task(t, now, timeout); |
e162b39a MSB |
172 | } while_each_thread(g, t); |
173 | unlock: | |
94be52dc | 174 | rcu_read_unlock(); |
e162b39a MSB |
175 | } |
176 | ||
177 | static void update_poll_jiffies(void) | |
178 | { | |
179 | /* timeout of 0 will disable the watchdog */ | |
180 | if (sysctl_hung_task_timeout_secs == 0) | |
181 | hung_task_poll_jiffies = MAX_SCHEDULE_TIMEOUT; | |
182 | else | |
183 | hung_task_poll_jiffies = sysctl_hung_task_timeout_secs * HZ / 2; | |
184 | } | |
185 | ||
186 | /* | |
187 | * Process updating of timeout sysctl | |
188 | */ | |
189 | int proc_dohung_task_timeout_secs(struct ctl_table *table, int write, | |
190 | struct file *filp, void __user *buffer, | |
191 | size_t *lenp, loff_t *ppos) | |
192 | { | |
193 | int ret; | |
194 | ||
195 | ret = proc_doulongvec_minmax(table, write, filp, buffer, lenp, ppos); | |
196 | ||
197 | if (ret || !write) | |
198 | goto out; | |
199 | ||
200 | update_poll_jiffies(); | |
201 | ||
202 | wake_up_process(watchdog_task); | |
203 | ||
204 | out: | |
205 | return ret; | |
206 | } | |
207 | ||
208 | /* | |
209 | * kthread which checks for tasks stuck in D state | |
210 | */ | |
211 | static int watchdog(void *dummy) | |
212 | { | |
213 | set_user_nice(current, 0); | |
214 | update_poll_jiffies(); | |
215 | ||
216 | for ( ; ; ) { | |
603a148f MSB |
217 | unsigned long timeout; |
218 | ||
e162b39a | 219 | while (schedule_timeout_interruptible(hung_task_poll_jiffies)); |
603a148f MSB |
220 | |
221 | /* | |
222 | * Need to cache timeout here to avoid timeout being set | |
223 | * to 0 via sysctl while inside check_hung_*_tasks(). | |
224 | */ | |
225 | timeout = sysctl_hung_task_timeout_secs; | |
226 | if (timeout) | |
227 | check_hung_uninterruptible_tasks(timeout); | |
e162b39a MSB |
228 | } |
229 | ||
230 | return 0; | |
231 | } | |
232 | ||
233 | static int __init hung_task_init(void) | |
234 | { | |
235 | atomic_notifier_chain_register(&panic_notifier_list, &panic_block); | |
236 | watchdog_task = kthread_run(watchdog, NULL, "khungtaskd"); | |
237 | ||
238 | return 0; | |
239 | } | |
240 | ||
241 | module_init(hung_task_init); |