Merge branch 'for-next' of git://git.samba.org/sfrench/cifs-2.6
[platform/adaptation/renesas_rcar/renesas_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         sysctl_hung_task_panic = simple_strtoul(str, NULL, 0);
56
57         return 1;
58 }
59 __setup("hung_task_panic=", hung_task_panic_setup);
60
61 static int
62 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
63 {
64         did_panic = 1;
65
66         return NOTIFY_DONE;
67 }
68
69 static struct notifier_block panic_block = {
70         .notifier_call = hung_task_panic,
71 };
72
73 static void check_hung_task(struct task_struct *t, unsigned long timeout)
74 {
75         unsigned long switch_count = t->nvcsw + t->nivcsw;
76
77         /*
78          * Ensure the task is not frozen.
79          * Also, skip vfork and any other user process that freezer should skip.
80          */
81         if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
82             return;
83
84         /*
85          * When a freshly created task is scheduled once, changes its state to
86          * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
87          * musn't be checked.
88          */
89         if (unlikely(!switch_count))
90                 return;
91
92         if (switch_count != t->last_switch_count) {
93                 t->last_switch_count = switch_count;
94                 return;
95         }
96
97         trace_sched_process_hang(t);
98
99         if (!sysctl_hung_task_warnings)
100                 return;
101
102         if (sysctl_hung_task_warnings > 0)
103                 sysctl_hung_task_warnings--;
104
105         /*
106          * Ok, the task did not get scheduled for more than 2 minutes,
107          * complain:
108          */
109         pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
110                 t->comm, t->pid, timeout);
111         pr_err("      %s %s %.*s\n",
112                 print_tainted(), init_utsname()->release,
113                 (int)strcspn(init_utsname()->version, " "),
114                 init_utsname()->version);
115         pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
116                 " disables this message.\n");
117         sched_show_task(t);
118         debug_show_held_locks(t);
119
120         touch_nmi_watchdog();
121
122         if (sysctl_hung_task_panic) {
123                 trigger_all_cpu_backtrace();
124                 panic("hung_task: blocked tasks");
125         }
126 }
127
128 /*
129  * To avoid extending the RCU grace period for an unbounded amount of time,
130  * periodically exit the critical section and enter a new one.
131  *
132  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
133  * to exit the grace period. For classic RCU, a reschedule is required.
134  */
135 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
136 {
137         bool can_cont;
138
139         get_task_struct(g);
140         get_task_struct(t);
141         rcu_read_unlock();
142         cond_resched();
143         rcu_read_lock();
144         can_cont = pid_alive(g) && pid_alive(t);
145         put_task_struct(t);
146         put_task_struct(g);
147
148         return can_cont;
149 }
150
151 /*
152  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
153  * a really long time (120 seconds). If that happens, print out
154  * a warning.
155  */
156 static void check_hung_uninterruptible_tasks(unsigned long timeout)
157 {
158         int max_count = sysctl_hung_task_check_count;
159         int batch_count = HUNG_TASK_BATCHING;
160         struct task_struct *g, *t;
161
162         /*
163          * If the system crashed already then all bets are off,
164          * do not report extra hung tasks:
165          */
166         if (test_taint(TAINT_DIE) || did_panic)
167                 return;
168
169         rcu_read_lock();
170         do_each_thread(g, t) {
171                 if (!max_count--)
172                         goto unlock;
173                 if (!--batch_count) {
174                         batch_count = HUNG_TASK_BATCHING;
175                         if (!rcu_lock_break(g, t))
176                                 goto unlock;
177                 }
178                 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
179                 if (t->state == TASK_UNINTERRUPTIBLE)
180                         check_hung_task(t, timeout);
181         } while_each_thread(g, t);
182  unlock:
183         rcu_read_unlock();
184 }
185
186 static unsigned long timeout_jiffies(unsigned long timeout)
187 {
188         /* timeout of 0 will disable the watchdog */
189         return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT;
190 }
191
192 /*
193  * Process updating of timeout sysctl
194  */
195 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
196                                   void __user *buffer,
197                                   size_t *lenp, loff_t *ppos)
198 {
199         int ret;
200
201         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
202
203         if (ret || !write)
204                 goto out;
205
206         wake_up_process(watchdog_task);
207
208  out:
209         return ret;
210 }
211
212 static atomic_t reset_hung_task = ATOMIC_INIT(0);
213
214 void reset_hung_task_detector(void)
215 {
216         atomic_set(&reset_hung_task, 1);
217 }
218 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
219
220 /*
221  * kthread which checks for tasks stuck in D state
222  */
223 static int watchdog(void *dummy)
224 {
225         set_user_nice(current, 0);
226
227         for ( ; ; ) {
228                 unsigned long timeout = sysctl_hung_task_timeout_secs;
229
230                 while (schedule_timeout_interruptible(timeout_jiffies(timeout)))
231                         timeout = sysctl_hung_task_timeout_secs;
232
233                 if (atomic_xchg(&reset_hung_task, 0))
234                         continue;
235
236                 check_hung_uninterruptible_tasks(timeout);
237         }
238
239         return 0;
240 }
241
242 static int __init hung_task_init(void)
243 {
244         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
245         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
246
247         return 0;
248 }
249
250 module_init(hung_task_init);