Merge remote-tracking branch 'rcu/rcu/next'
[deliverable/linux.git] / kernel / hung_task.c
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_all_locks();
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 for_each_process_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 }
184 unlock:
185 rcu_read_unlock();
186 }
187
188 static long hung_timeout_jiffies(unsigned long last_checked,
189 unsigned long timeout)
190 {
191 /* timeout of 0 will disable the watchdog */
192 return timeout ? last_checked - jiffies + timeout * HZ :
193 MAX_SCHEDULE_TIMEOUT;
194 }
195
196 /*
197 * Process updating of timeout sysctl
198 */
199 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
200 void __user *buffer,
201 size_t *lenp, loff_t *ppos)
202 {
203 int ret;
204
205 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
206
207 if (ret || !write)
208 goto out;
209
210 wake_up_process(watchdog_task);
211
212 out:
213 return ret;
214 }
215
216 static atomic_t reset_hung_task = ATOMIC_INIT(0);
217
218 void reset_hung_task_detector(void)
219 {
220 atomic_set(&reset_hung_task, 1);
221 }
222 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
223
224 /*
225 * kthread which checks for tasks stuck in D state
226 */
227 static int watchdog(void *dummy)
228 {
229 unsigned long hung_last_checked = jiffies;
230
231 set_user_nice(current, 0);
232
233 for ( ; ; ) {
234 unsigned long timeout = sysctl_hung_task_timeout_secs;
235 long t = hung_timeout_jiffies(hung_last_checked, timeout);
236
237 if (t <= 0) {
238 if (!atomic_xchg(&reset_hung_task, 0))
239 check_hung_uninterruptible_tasks(timeout);
240 hung_last_checked = jiffies;
241 continue;
242 }
243 schedule_timeout_interruptible(t);
244 }
245
246 return 0;
247 }
248
249 static int __init hung_task_init(void)
250 {
251 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
252 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
253
254 return 0;
255 }
256 subsys_initcall(hung_task_init);
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