Root/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/module.h>
17#include <linux/sysctl.h>
18
19/*
20 * The number of tasks checked:
21 */
22unsigned 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
32
33/*
34 * Zero means infinite timeout - no checking done:
35 */
36unsigned long __read_mostly sysctl_hung_task_timeout_secs = 120;
37
38unsigned long __read_mostly sysctl_hung_task_warnings = 10;
39
40static int __read_mostly did_panic;
41
42static struct task_struct *watchdog_task;
43
44/*
45 * Should we panic (and reboot, if panic_timeout= is set) when a
46 * hung task is detected:
47 */
48unsigned int __read_mostly sysctl_hung_task_panic =
49                CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
50
51static int __init hung_task_panic_setup(char *str)
52{
53    sysctl_hung_task_panic = simple_strtoul(str, NULL, 0);
54
55    return 1;
56}
57__setup("hung_task_panic=", hung_task_panic_setup);
58
59static int
60hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
61{
62    did_panic = 1;
63
64    return NOTIFY_DONE;
65}
66
67static struct notifier_block panic_block = {
68    .notifier_call = hung_task_panic,
69};
70
71static void check_hung_task(struct task_struct *t, unsigned long timeout)
72{
73    unsigned long switch_count = t->nvcsw + t->nivcsw;
74
75    /*
76     * Ensure the task is not frozen.
77     * Also, when a freshly created task is scheduled once, changes
78     * its state to TASK_UNINTERRUPTIBLE without having ever been
79     * switched out once, it musn't be checked.
80     */
81    if (unlikely(t->flags & PF_FROZEN || !switch_count))
82        return;
83
84    if (switch_count != t->last_switch_count) {
85        t->last_switch_count = switch_count;
86        return;
87    }
88    if (!sysctl_hung_task_warnings)
89        return;
90    sysctl_hung_task_warnings--;
91
92    /*
93     * Ok, the task did not get scheduled for more than 2 minutes,
94     * complain:
95     */
96    printk(KERN_ERR "INFO: task %s:%d blocked for more than "
97            "%ld seconds.\n", t->comm, t->pid, timeout);
98    printk(KERN_ERR "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
99            " disables this message.\n");
100    sched_show_task(t);
101    debug_show_held_locks(t);
102
103    touch_nmi_watchdog();
104
105    if (sysctl_hung_task_panic)
106        panic("hung_task: blocked tasks");
107}
108
109/*
110 * To avoid extending the RCU grace period for an unbounded amount of time,
111 * periodically exit the critical section and enter a new one.
112 *
113 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
114 * to exit the grace period. For classic RCU, a reschedule is required.
115 */
116static void rcu_lock_break(struct task_struct *g, struct task_struct *t)
117{
118    get_task_struct(g);
119    get_task_struct(t);
120    rcu_read_unlock();
121    cond_resched();
122    rcu_read_lock();
123    put_task_struct(t);
124    put_task_struct(g);
125}
126
127/*
128 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
129 * a really long time (120 seconds). If that happens, print out
130 * a warning.
131 */
132static void check_hung_uninterruptible_tasks(unsigned long timeout)
133{
134    int max_count = sysctl_hung_task_check_count;
135    int batch_count = HUNG_TASK_BATCHING;
136    struct task_struct *g, *t;
137
138    /*
139     * If the system crashed already then all bets are off,
140     * do not report extra hung tasks:
141     */
142    if (test_taint(TAINT_DIE) || did_panic)
143        return;
144
145    rcu_read_lock();
146    do_each_thread(g, t) {
147        if (!max_count--)
148            goto unlock;
149        if (!--batch_count) {
150            batch_count = HUNG_TASK_BATCHING;
151            rcu_lock_break(g, t);
152            /* Exit if t or g was unhashed during refresh. */
153            if (t->state == TASK_DEAD || g->state == TASK_DEAD)
154                goto unlock;
155        }
156        /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
157        if (t->state == TASK_UNINTERRUPTIBLE)
158            check_hung_task(t, timeout);
159    } while_each_thread(g, t);
160 unlock:
161    rcu_read_unlock();
162}
163
164static unsigned long timeout_jiffies(unsigned long timeout)
165{
166    /* timeout of 0 will disable the watchdog */
167    return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT;
168}
169
170/*
171 * Process updating of timeout sysctl
172 */
173int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
174                  void __user *buffer,
175                  size_t *lenp, loff_t *ppos)
176{
177    int ret;
178
179    ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
180
181    if (ret || !write)
182        goto out;
183
184    wake_up_process(watchdog_task);
185
186 out:
187    return ret;
188}
189
190/*
191 * kthread which checks for tasks stuck in D state
192 */
193static int watchdog(void *dummy)
194{
195    set_user_nice(current, 0);
196
197    for ( ; ; ) {
198        unsigned long timeout = sysctl_hung_task_timeout_secs;
199
200        while (schedule_timeout_interruptible(timeout_jiffies(timeout)))
201            timeout = sysctl_hung_task_timeout_secs;
202
203        check_hung_uninterruptible_tasks(timeout);
204    }
205
206    return 0;
207}
208
209static int __init hung_task_init(void)
210{
211    atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
212    watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
213
214    return 0;
215}
216
217module_init(hung_task_init);
218

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