xfs: avoid getting stuck during async inode flushes
[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / kernel / hung_task.c
blob53ead174da2f0a7c7849df4ef81b60a96fe7c4f6
1 /*
2 * Detect Hung Task
4 * kernel/hung_task.c - kernel thread for detecting tasks stuck in D state
6 */
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>
20 * The number of tasks checked:
22 unsigned long __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
25 * Limit number of tasks checked in a batch.
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.
31 #define HUNG_TASK_BATCHING 1024
34 * Zero means infinite timeout - no checking done:
36 unsigned long __read_mostly sysctl_hung_task_timeout_secs = 120;
38 unsigned long __read_mostly sysctl_hung_task_warnings = 10;
40 static int __read_mostly did_panic;
42 static struct task_struct *watchdog_task;
45 * Should we panic (and reboot, if panic_timeout= is set) when a
46 * hung task is detected:
48 unsigned int __read_mostly sysctl_hung_task_panic =
49 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
51 static int __init hung_task_panic_setup(char *str)
53 sysctl_hung_task_panic = simple_strtoul(str, NULL, 0);
55 return 1;
57 __setup("hung_task_panic=", hung_task_panic_setup);
59 static int
60 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
62 did_panic = 1;
64 return NOTIFY_DONE;
67 static struct notifier_block panic_block = {
68 .notifier_call = hung_task_panic,
71 static void check_hung_task(struct task_struct *t, unsigned long timeout)
73 unsigned long switch_count = t->nvcsw + t->nivcsw;
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.
81 if (unlikely(t->flags & PF_FROZEN || !switch_count))
82 return;
84 if (switch_count != t->last_switch_count) {
85 t->last_switch_count = switch_count;
86 return;
88 if (!sysctl_hung_task_warnings)
89 return;
90 sysctl_hung_task_warnings--;
93 * Ok, the task did not get scheduled for more than 2 minutes,
94 * complain:
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);
103 touch_nmi_watchdog();
105 if (sysctl_hung_task_panic)
106 panic("hung_task: blocked tasks");
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.
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.
116 static void rcu_lock_break(struct task_struct *g, struct task_struct *t)
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);
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.
132 static void check_hung_uninterruptible_tasks(unsigned long timeout)
134 int max_count = sysctl_hung_task_check_count;
135 int batch_count = HUNG_TASK_BATCHING;
136 struct task_struct *g, *t;
139 * If the system crashed already then all bets are off,
140 * do not report extra hung tasks:
142 if (test_taint(TAINT_DIE) || did_panic)
143 return;
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;
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();
164 static unsigned long timeout_jiffies(unsigned long timeout)
166 /* timeout of 0 will disable the watchdog */
167 return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT;
171 * Process updating of timeout sysctl
173 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
174 void __user *buffer,
175 size_t *lenp, loff_t *ppos)
177 int ret;
179 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
181 if (ret || !write)
182 goto out;
184 wake_up_process(watchdog_task);
186 out:
187 return ret;
191 * kthread which checks for tasks stuck in D state
193 static int watchdog(void *dummy)
195 set_user_nice(current, 0);
197 for ( ; ; ) {
198 unsigned long timeout = sysctl_hung_task_timeout_secs;
200 while (schedule_timeout_interruptible(timeout_jiffies(timeout)))
201 timeout = sysctl_hung_task_timeout_secs;
203 check_hung_uninterruptible_tasks(timeout);
206 return 0;
209 static int __init hung_task_init(void)
211 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
212 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
214 return 0;
217 module_init(hung_task_init);