projects/linux·blob v3.12-rc6 · refs

233 lines · 5.4 KiB

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
20/*
21 * The number of tasks checked:
22 */
23unsigned long __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
24
25/*
26 * Limit number of tasks checked in a batch.
27 *
28 * This value controls the preemptibility of khungtaskd since preemption
29 * is disabled during the critical section. It also controls the size of
30 * the RCU grace period. So it needs to be upper-bound.
31 */
32#define HUNG_TASK_BATCHING 1024
33
34/*
35 * Zero means infinite timeout - no checking done:
36 */
37unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
38
39unsigned long __read_mostly sysctl_hung_task_warnings = 10;
40
41static int __read_mostly did_panic;
42
43static 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 */
49unsigned int __read_mostly sysctl_hung_task_panic =
50 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
51
52static 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
60static int
61hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
62{
63 did_panic = 1;
64
65 return NOTIFY_DONE;
66}
67
68static struct notifier_block panic_block = {
69 .notifier_call = hung_task_panic,
70};
71
72static void check_hung_task(struct task_struct *t, unsigned long timeout)
73{
74 unsigned long switch_count = t->nvcsw + t->nivcsw;
75
76 /*
77 * Ensure the task is not frozen.
78 * Also, skip vfork and any other user process that freezer should skip.
79 */
80 if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
81 return;
82
83 /*
84 * When a freshly created task is scheduled once, changes its state to
85 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
86 * musn't be checked.
87 */
88 if (unlikely(!switch_count))
89 return;
90
91 if (switch_count != t->last_switch_count) {
92 t->last_switch_count = switch_count;
93 return;
94 }
95 if (!sysctl_hung_task_warnings)
96 return;
97 sysctl_hung_task_warnings--;
98
99 /*
100 * Ok, the task did not get scheduled for more than 2 minutes,
101 * complain:
102 */
103 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
104 t->comm, t->pid, timeout);
105 pr_err(" %s %s %.*s\n",
106 print_tainted(), init_utsname()->release,
107 (int)strcspn(init_utsname()->version, " "),
108 init_utsname()->version);
109 pr_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 touch_nmi_watchdog();
115
116 if (sysctl_hung_task_panic) {
117 trigger_all_cpu_backtrace();
118 panic("hung_task: blocked tasks");
119 }
120}
121
122/*
123 * To avoid extending the RCU grace period for an unbounded amount of time,
124 * periodically exit the critical section and enter a new one.
125 *
126 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
127 * to exit the grace period. For classic RCU, a reschedule is required.
128 */
129static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
130{
131 bool can_cont;
132
133 get_task_struct(g);
134 get_task_struct(t);
135 rcu_read_unlock();
136 cond_resched();
137 rcu_read_lock();
138 can_cont = pid_alive(g) && pid_alive(t);
139 put_task_struct(t);
140 put_task_struct(g);
141
142 return can_cont;
143}
144
145/*
146 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
147 * a really long time (120 seconds). If that happens, print out
148 * a warning.
149 */
150static void check_hung_uninterruptible_tasks(unsigned long timeout)
151{
152 int max_count = sysctl_hung_task_check_count;
153 int batch_count = HUNG_TASK_BATCHING;
154 struct task_struct *g, *t;
155
156 /*
157 * If the system crashed already then all bets are off,
158 * do not report extra hung tasks:
159 */
160 if (test_taint(TAINT_DIE) || did_panic)
161 return;
162
163 rcu_read_lock();
164 do_each_thread(g, t) {
165 if (!max_count--)
166 goto unlock;
167 if (!--batch_count) {
168 batch_count = HUNG_TASK_BATCHING;
169 if (!rcu_lock_break(g, t))
170 goto unlock;
171 }
172 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
173 if (t->state == TASK_UNINTERRUPTIBLE)
174 check_hung_task(t, timeout);
175 } while_each_thread(g, t);
176 unlock:
177 rcu_read_unlock();
178}
179
180static unsigned long timeout_jiffies(unsigned long timeout)
181{
182 /* timeout of 0 will disable the watchdog */
183 return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT;
184}
185
186/*
187 * Process updating of timeout sysctl
188 */
189int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
190 void __user *buffer,
191 size_t *lenp, loff_t *ppos)
192{
193 int ret;
194
195 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
196
197 if (ret || !write)
198 goto out;
199
200 wake_up_process(watchdog_task);
201
202 out:
203 return ret;
204}
205
206/*
207 * kthread which checks for tasks stuck in D state
208 */
209static int watchdog(void *dummy)
210{
211 set_user_nice(current, 0);
212
213 for ( ; ; ) {
214 unsigned long timeout = sysctl_hung_task_timeout_secs;
215
216 while (schedule_timeout_interruptible(timeout_jiffies(timeout)))
217 timeout = sysctl_hung_task_timeout_secs;
218
219 check_hung_uninterruptible_tasks(timeout);
220 }
221
222 return 0;
223}
224
225static int __init hung_task_init(void)
226{
227 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
228 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
229
230 return 0;
231}
232
233module_init(hung_task_init);