Commit | Line | Data |
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e162b39a MSB |
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> | |
9984de1a | 16 | #include <linux/export.h> |
e162b39a | 17 | #include <linux/sysctl.h> |
41e85ce8 | 18 | #include <linux/utsname.h> |
e162b39a MSB |
19 | |
20 | /* | |
ce9dbe24 | 21 | * The number of tasks checked: |
e162b39a | 22 | */ |
ce9dbe24 MSB |
23 | unsigned 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 | |
e162b39a MSB |
33 | |
34 | /* | |
35 | * Zero means infinite timeout - no checking done: | |
36 | */ | |
e11feaa1 | 37 | unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT; |
e162b39a MSB |
38 | |
39 | unsigned long __read_mostly sysctl_hung_task_warnings = 10; | |
40 | ||
41 | static int __read_mostly did_panic; | |
42 | ||
43 | static 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 | */ | |
49 | unsigned int __read_mostly sysctl_hung_task_panic = | |
50 | CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE; | |
51 | ||
52 | static 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 | ||
60 | static int | |
61 | hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr) | |
62 | { | |
63 | did_panic = 1; | |
64 | ||
65 | return NOTIFY_DONE; | |
66 | } | |
67 | ||
68 | static struct notifier_block panic_block = { | |
69 | .notifier_call = hung_task_panic, | |
70 | }; | |
71 | ||
17406b82 | 72 | static void check_hung_task(struct task_struct *t, unsigned long timeout) |
e162b39a MSB |
73 | { |
74 | unsigned long switch_count = t->nvcsw + t->nivcsw; | |
75 | ||
cf2592f5 FW |
76 | /* |
77 | * Ensure the task is not frozen. | |
f9fab10b | 78 | * Also, skip vfork and any other user process that freezer should skip. |
cf2592f5 | 79 | */ |
f9fab10b MSB |
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)) | |
e162b39a MSB |
89 | return; |
90 | ||
17406b82 | 91 | if (switch_count != t->last_switch_count) { |
e162b39a | 92 | t->last_switch_count = switch_count; |
e162b39a MSB |
93 | return; |
94 | } | |
e162b39a MSB |
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 | */ | |
41e85ce8 ON |
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"); | |
e162b39a | 111 | sched_show_task(t); |
f1b499f0 | 112 | debug_show_held_locks(t); |
e162b39a | 113 | |
e162b39a MSB |
114 | touch_nmi_watchdog(); |
115 | ||
625056b6 SL |
116 | if (sysctl_hung_task_panic) { |
117 | trigger_all_cpu_backtrace(); | |
e162b39a | 118 | panic("hung_task: blocked tasks"); |
625056b6 | 119 | } |
e162b39a MSB |
120 | } |
121 | ||
ce9dbe24 MSB |
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 | |
6a103b0d | 127 | * to exit the grace period. For classic RCU, a reschedule is required. |
ce9dbe24 | 128 | */ |
6027ce49 | 129 | static bool rcu_lock_break(struct task_struct *g, struct task_struct *t) |
ce9dbe24 | 130 | { |
6027ce49 ON |
131 | bool can_cont; |
132 | ||
ce9dbe24 MSB |
133 | get_task_struct(g); |
134 | get_task_struct(t); | |
135 | rcu_read_unlock(); | |
136 | cond_resched(); | |
137 | rcu_read_lock(); | |
6027ce49 | 138 | can_cont = pid_alive(g) && pid_alive(t); |
ce9dbe24 MSB |
139 | put_task_struct(t); |
140 | put_task_struct(g); | |
6027ce49 ON |
141 | |
142 | return can_cont; | |
ce9dbe24 MSB |
143 | } |
144 | ||
e162b39a MSB |
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 | */ | |
603a148f | 150 | static void check_hung_uninterruptible_tasks(unsigned long timeout) |
e162b39a MSB |
151 | { |
152 | int max_count = sysctl_hung_task_check_count; | |
ce9dbe24 | 153 | int batch_count = HUNG_TASK_BATCHING; |
e162b39a MSB |
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 | ||
94be52dc | 163 | rcu_read_lock(); |
e162b39a | 164 | do_each_thread(g, t) { |
e5af0226 | 165 | if (!max_count--) |
e162b39a | 166 | goto unlock; |
ce9dbe24 MSB |
167 | if (!--batch_count) { |
168 | batch_count = HUNG_TASK_BATCHING; | |
6027ce49 | 169 | if (!rcu_lock_break(g, t)) |
ce9dbe24 MSB |
170 | goto unlock; |
171 | } | |
e162b39a MSB |
172 | /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */ |
173 | if (t->state == TASK_UNINTERRUPTIBLE) | |
17406b82 | 174 | check_hung_task(t, timeout); |
e162b39a MSB |
175 | } while_each_thread(g, t); |
176 | unlock: | |
94be52dc | 177 | rcu_read_unlock(); |
e162b39a MSB |
178 | } |
179 | ||
17406b82 | 180 | static unsigned long timeout_jiffies(unsigned long timeout) |
e162b39a MSB |
181 | { |
182 | /* timeout of 0 will disable the watchdog */ | |
17406b82 | 183 | return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT; |
e162b39a MSB |
184 | } |
185 | ||
186 | /* | |
187 | * Process updating of timeout sysctl | |
188 | */ | |
189 | int proc_dohung_task_timeout_secs(struct ctl_table *table, int write, | |
8d65af78 | 190 | void __user *buffer, |
e162b39a MSB |
191 | size_t *lenp, loff_t *ppos) |
192 | { | |
193 | int ret; | |
194 | ||
8d65af78 | 195 | ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); |
e162b39a MSB |
196 | |
197 | if (ret || !write) | |
198 | goto out; | |
199 | ||
e162b39a MSB |
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 | */ | |
209 | static int watchdog(void *dummy) | |
210 | { | |
211 | set_user_nice(current, 0); | |
e162b39a MSB |
212 | |
213 | for ( ; ; ) { | |
17406b82 | 214 | unsigned long timeout = sysctl_hung_task_timeout_secs; |
603a148f | 215 | |
17406b82 MSB |
216 | while (schedule_timeout_interruptible(timeout_jiffies(timeout))) |
217 | timeout = sysctl_hung_task_timeout_secs; | |
603a148f | 218 | |
17406b82 | 219 | check_hung_uninterruptible_tasks(timeout); |
e162b39a MSB |
220 | } |
221 | ||
222 | return 0; | |
223 | } | |
224 | ||
225 | static 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 | ||
233 | module_init(hung_task_init); |