Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi...
[pandora-kernel.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_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);