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/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 */
24int __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 */
38unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
39
40int __read_mostly sysctl_hung_task_warnings = 10;
41
42static int __read_mostly did_panic;
43
44static 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 */
50unsigned int __read_mostly sysctl_hung_task_panic =
51                CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
52
53static 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
61static int
62hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
63{
64    did_panic = 1;
65
66    return NOTIFY_DONE;
67}
68
69static struct notifier_block panic_block = {
70    .notifier_call = hung_task_panic,
71};
72
73static 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 */
135static 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 */
156static 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
186static 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 */
195int 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
212static atomic_t reset_hung_task = ATOMIC_INIT(0);
213
214void reset_hung_task_detector(void)
215{
216    atomic_set(&reset_hung_task, 1);
217}
218EXPORT_SYMBOL_GPL(reset_hung_task_detector);
219
220/*
221 * kthread which checks for tasks stuck in D state
222 */
223static 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
242static 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}
249subsys_initcall(hung_task_init);
250

Archive Download this file



interactive