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> |
6a716c90 | 19 | #include <trace/events/sched.h> |
e162b39a MSB |
20 | |
21 | /* | |
ce9dbe24 | 22 | * The number of tasks checked: |
e162b39a | 23 | */ |
cd64647f | 24 | int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT; |
ce9dbe24 MSB |
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 | |
e162b39a MSB |
34 | |
35 | /* | |
36 | * Zero means infinite timeout - no checking done: | |
37 | */ | |
e11feaa1 | 38 | unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT; |
e162b39a | 39 | |
270750db | 40 | int __read_mostly sysctl_hung_task_warnings = 10; |
e162b39a MSB |
41 | |
42 | static int __read_mostly did_panic; | |
43 | ||
44 | static 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 | */ | |
50 | unsigned int __read_mostly sysctl_hung_task_panic = | |
51 | CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE; | |
52 | ||
53 | static int __init hung_task_panic_setup(char *str) | |
54 | { | |
b51dbec6 | 55 | int rc = kstrtouint(str, 0, &sysctl_hung_task_panic); |
e162b39a | 56 | |
b51dbec6 FF |
57 | if (rc) |
58 | return rc; | |
e162b39a MSB |
59 | return 1; |
60 | } | |
61 | __setup("hung_task_panic=", hung_task_panic_setup); | |
62 | ||
63 | static int | |
64 | hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr) | |
65 | { | |
66 | did_panic = 1; | |
67 | ||
68 | return NOTIFY_DONE; | |
69 | } | |
70 | ||
71 | static struct notifier_block panic_block = { | |
72 | .notifier_call = hung_task_panic, | |
73 | }; | |
74 | ||
17406b82 | 75 | static void check_hung_task(struct task_struct *t, unsigned long timeout) |
e162b39a MSB |
76 | { |
77 | unsigned long switch_count = t->nvcsw + t->nivcsw; | |
78 | ||
cf2592f5 FW |
79 | /* |
80 | * Ensure the task is not frozen. | |
f9fab10b | 81 | * Also, skip vfork and any other user process that freezer should skip. |
cf2592f5 | 82 | */ |
f9fab10b MSB |
83 | if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP))) |
84 | return; | |
85 | ||
86 | /* | |
87 | * When a freshly created task is scheduled once, changes its state to | |
88 | * TASK_UNINTERRUPTIBLE without having ever been switched out once, it | |
89 | * musn't be checked. | |
90 | */ | |
91 | if (unlikely(!switch_count)) | |
e162b39a MSB |
92 | return; |
93 | ||
17406b82 | 94 | if (switch_count != t->last_switch_count) { |
e162b39a | 95 | t->last_switch_count = switch_count; |
e162b39a MSB |
96 | return; |
97 | } | |
6a716c90 ON |
98 | |
99 | trace_sched_process_hang(t); | |
100 | ||
e162b39a MSB |
101 | if (!sysctl_hung_task_warnings) |
102 | return; | |
270750db AT |
103 | |
104 | if (sysctl_hung_task_warnings > 0) | |
105 | sysctl_hung_task_warnings--; | |
e162b39a MSB |
106 | |
107 | /* | |
108 | * Ok, the task did not get scheduled for more than 2 minutes, | |
109 | * complain: | |
110 | */ | |
41e85ce8 ON |
111 | pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n", |
112 | t->comm, t->pid, timeout); | |
113 | pr_err(" %s %s %.*s\n", | |
114 | print_tainted(), init_utsname()->release, | |
115 | (int)strcspn(init_utsname()->version, " "), | |
116 | init_utsname()->version); | |
117 | pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\"" | |
118 | " disables this message.\n"); | |
e162b39a | 119 | sched_show_task(t); |
b2d4c2ed | 120 | debug_show_all_locks(); |
e162b39a | 121 | |
e162b39a MSB |
122 | touch_nmi_watchdog(); |
123 | ||
625056b6 SL |
124 | if (sysctl_hung_task_panic) { |
125 | trigger_all_cpu_backtrace(); | |
e162b39a | 126 | panic("hung_task: blocked tasks"); |
625056b6 | 127 | } |
e162b39a MSB |
128 | } |
129 | ||
ce9dbe24 MSB |
130 | /* |
131 | * To avoid extending the RCU grace period for an unbounded amount of time, | |
132 | * periodically exit the critical section and enter a new one. | |
133 | * | |
134 | * For preemptible RCU it is sufficient to call rcu_read_unlock in order | |
6a103b0d | 135 | * to exit the grace period. For classic RCU, a reschedule is required. |
ce9dbe24 | 136 | */ |
6027ce49 | 137 | static bool rcu_lock_break(struct task_struct *g, struct task_struct *t) |
ce9dbe24 | 138 | { |
6027ce49 ON |
139 | bool can_cont; |
140 | ||
ce9dbe24 MSB |
141 | get_task_struct(g); |
142 | get_task_struct(t); | |
143 | rcu_read_unlock(); | |
144 | cond_resched(); | |
145 | rcu_read_lock(); | |
6027ce49 | 146 | can_cont = pid_alive(g) && pid_alive(t); |
ce9dbe24 MSB |
147 | put_task_struct(t); |
148 | put_task_struct(g); | |
6027ce49 ON |
149 | |
150 | return can_cont; | |
ce9dbe24 MSB |
151 | } |
152 | ||
e162b39a MSB |
153 | /* |
154 | * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for | |
155 | * a really long time (120 seconds). If that happens, print out | |
156 | * a warning. | |
157 | */ | |
603a148f | 158 | static void check_hung_uninterruptible_tasks(unsigned long timeout) |
e162b39a MSB |
159 | { |
160 | int max_count = sysctl_hung_task_check_count; | |
ce9dbe24 | 161 | int batch_count = HUNG_TASK_BATCHING; |
e162b39a MSB |
162 | struct task_struct *g, *t; |
163 | ||
164 | /* | |
165 | * If the system crashed already then all bets are off, | |
166 | * do not report extra hung tasks: | |
167 | */ | |
168 | if (test_taint(TAINT_DIE) || did_panic) | |
169 | return; | |
170 | ||
94be52dc | 171 | rcu_read_lock(); |
972fae69 | 172 | for_each_process_thread(g, t) { |
e5af0226 | 173 | if (!max_count--) |
e162b39a | 174 | goto unlock; |
ce9dbe24 MSB |
175 | if (!--batch_count) { |
176 | batch_count = HUNG_TASK_BATCHING; | |
6027ce49 | 177 | if (!rcu_lock_break(g, t)) |
ce9dbe24 MSB |
178 | goto unlock; |
179 | } | |
e162b39a MSB |
180 | /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */ |
181 | if (t->state == TASK_UNINTERRUPTIBLE) | |
17406b82 | 182 | check_hung_task(t, timeout); |
972fae69 | 183 | } |
e162b39a | 184 | unlock: |
94be52dc | 185 | rcu_read_unlock(); |
e162b39a MSB |
186 | } |
187 | ||
b4aa14a6 TH |
188 | static long hung_timeout_jiffies(unsigned long last_checked, |
189 | unsigned long timeout) | |
e162b39a MSB |
190 | { |
191 | /* timeout of 0 will disable the watchdog */ | |
b4aa14a6 TH |
192 | return timeout ? last_checked - jiffies + timeout * HZ : |
193 | MAX_SCHEDULE_TIMEOUT; | |
e162b39a MSB |
194 | } |
195 | ||
196 | /* | |
197 | * Process updating of timeout sysctl | |
198 | */ | |
199 | int proc_dohung_task_timeout_secs(struct ctl_table *table, int write, | |
8d65af78 | 200 | void __user *buffer, |
e162b39a MSB |
201 | size_t *lenp, loff_t *ppos) |
202 | { | |
203 | int ret; | |
204 | ||
8d65af78 | 205 | ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); |
e162b39a MSB |
206 | |
207 | if (ret || !write) | |
208 | goto out; | |
209 | ||
e162b39a MSB |
210 | wake_up_process(watchdog_task); |
211 | ||
212 | out: | |
213 | return ret; | |
214 | } | |
215 | ||
8b414521 MT |
216 | static atomic_t reset_hung_task = ATOMIC_INIT(0); |
217 | ||
218 | void reset_hung_task_detector(void) | |
219 | { | |
220 | atomic_set(&reset_hung_task, 1); | |
221 | } | |
222 | EXPORT_SYMBOL_GPL(reset_hung_task_detector); | |
223 | ||
e162b39a MSB |
224 | /* |
225 | * kthread which checks for tasks stuck in D state | |
226 | */ | |
227 | static int watchdog(void *dummy) | |
228 | { | |
b4aa14a6 TH |
229 | unsigned long hung_last_checked = jiffies; |
230 | ||
e162b39a | 231 | set_user_nice(current, 0); |
e162b39a MSB |
232 | |
233 | for ( ; ; ) { | |
17406b82 | 234 | unsigned long timeout = sysctl_hung_task_timeout_secs; |
b4aa14a6 | 235 | long t = hung_timeout_jiffies(hung_last_checked, timeout); |
603a148f | 236 | |
b4aa14a6 TH |
237 | if (t <= 0) { |
238 | if (!atomic_xchg(&reset_hung_task, 0)) | |
239 | check_hung_uninterruptible_tasks(timeout); | |
240 | hung_last_checked = jiffies; | |
8b414521 | 241 | continue; |
b4aa14a6 TH |
242 | } |
243 | schedule_timeout_interruptible(t); | |
e162b39a MSB |
244 | } |
245 | ||
246 | return 0; | |
247 | } | |
248 | ||
249 | static int __init hung_task_init(void) | |
250 | { | |
251 | atomic_notifier_chain_register(&panic_notifier_list, &panic_block); | |
252 | watchdog_task = kthread_run(watchdog, NULL, "khungtaskd"); | |
253 | ||
254 | return 0; | |
255 | } | |
c96d6660 | 256 | subsys_initcall(hung_task_init); |