| 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 | */ |
| 24 | int __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 | */ |
| 38 | unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT; |
| 39 | |
| 40 | int __read_mostly sysctl_hung_task_warnings = 10; |
| 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 | { |
| 55 | int rc = kstrtouint(str, 0, &sysctl_hung_task_panic); |
| 56 | |
| 57 | if (rc) |
| 58 | return rc; |
| 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 | |
| 75 | static void check_hung_task(struct task_struct *t, unsigned long timeout) |
| 76 | { |
| 77 | unsigned long switch_count = t->nvcsw + t->nivcsw; |
| 78 | |
| 79 | /* |
| 80 | * Ensure the task is not frozen. |
| 81 | * Also, skip vfork and any other user process that freezer should skip. |
| 82 | */ |
| 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)) |
| 92 | return; |
| 93 | |
| 94 | if (switch_count != t->last_switch_count) { |
| 95 | t->last_switch_count = switch_count; |
| 96 | return; |
| 97 | } |
| 98 | |
| 99 | trace_sched_process_hang(t); |
| 100 | |
| 101 | if (!sysctl_hung_task_warnings) |
| 102 | return; |
| 103 | |
| 104 | if (sysctl_hung_task_warnings > 0) |
| 105 | sysctl_hung_task_warnings--; |
| 106 | |
| 107 | /* |
| 108 | * Ok, the task did not get scheduled for more than 2 minutes, |
| 109 | * complain: |
| 110 | */ |
| 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"); |
| 119 | sched_show_task(t); |
| 120 | debug_show_held_locks(t); |
| 121 | |
| 122 | touch_nmi_watchdog(); |
| 123 | |
| 124 | if (sysctl_hung_task_panic) { |
| 125 | trigger_all_cpu_backtrace(); |
| 126 | panic("hung_task: blocked tasks"); |
| 127 | } |
| 128 | } |
| 129 | |
| 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 |
| 135 | * to exit the grace period. For classic RCU, a reschedule is required. |
| 136 | */ |
| 137 | static bool rcu_lock_break(struct task_struct *g, struct task_struct *t) |
| 138 | { |
| 139 | bool can_cont; |
| 140 | |
| 141 | get_task_struct(g); |
| 142 | get_task_struct(t); |
| 143 | rcu_read_unlock(); |
| 144 | cond_resched(); |
| 145 | rcu_read_lock(); |
| 146 | can_cont = pid_alive(g) && pid_alive(t); |
| 147 | put_task_struct(t); |
| 148 | put_task_struct(g); |
| 149 | |
| 150 | return can_cont; |
| 151 | } |
| 152 | |
| 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 | */ |
| 158 | static void check_hung_uninterruptible_tasks(unsigned long timeout) |
| 159 | { |
| 160 | int max_count = sysctl_hung_task_check_count; |
| 161 | int batch_count = HUNG_TASK_BATCHING; |
| 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 | |
| 171 | rcu_read_lock(); |
| 172 | for_each_process_thread(g, t) { |
| 173 | if (!max_count--) |
| 174 | goto unlock; |
| 175 | if (!--batch_count) { |
| 176 | batch_count = HUNG_TASK_BATCHING; |
| 177 | if (!rcu_lock_break(g, t)) |
| 178 | goto unlock; |
| 179 | } |
| 180 | /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */ |
| 181 | if (t->state == TASK_UNINTERRUPTIBLE) |
| 182 | check_hung_task(t, timeout); |
| 183 | } |
| 184 | unlock: |
| 185 | rcu_read_unlock(); |
| 186 | } |
| 187 | |
| 188 | static unsigned long timeout_jiffies(unsigned long timeout) |
| 189 | { |
| 190 | /* timeout of 0 will disable the watchdog */ |
| 191 | return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT; |
| 192 | } |
| 193 | |
| 194 | /* |
| 195 | * Process updating of timeout sysctl |
| 196 | */ |
| 197 | int proc_dohung_task_timeout_secs(struct ctl_table *table, int write, |
| 198 | void __user *buffer, |
| 199 | size_t *lenp, loff_t *ppos) |
| 200 | { |
| 201 | int ret; |
| 202 | |
| 203 | ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); |
| 204 | |
| 205 | if (ret || !write) |
| 206 | goto out; |
| 207 | |
| 208 | wake_up_process(watchdog_task); |
| 209 | |
| 210 | out: |
| 211 | return ret; |
| 212 | } |
| 213 | |
| 214 | static atomic_t reset_hung_task = ATOMIC_INIT(0); |
| 215 | |
| 216 | void reset_hung_task_detector(void) |
| 217 | { |
| 218 | atomic_set(&reset_hung_task, 1); |
| 219 | } |
| 220 | EXPORT_SYMBOL_GPL(reset_hung_task_detector); |
| 221 | |
| 222 | /* |
| 223 | * kthread which checks for tasks stuck in D state |
| 224 | */ |
| 225 | static int watchdog(void *dummy) |
| 226 | { |
| 227 | set_user_nice(current, 0); |
| 228 | |
| 229 | for ( ; ; ) { |
| 230 | unsigned long timeout = sysctl_hung_task_timeout_secs; |
| 231 | |
| 232 | while (schedule_timeout_interruptible(timeout_jiffies(timeout))) |
| 233 | timeout = sysctl_hung_task_timeout_secs; |
| 234 | |
| 235 | if (atomic_xchg(&reset_hung_task, 0)) |
| 236 | continue; |
| 237 | |
| 238 | check_hung_uninterruptible_tasks(timeout); |
| 239 | } |
| 240 | |
| 241 | return 0; |
| 242 | } |
| 243 | |
| 244 | static int __init hung_task_init(void) |
| 245 | { |
| 246 | atomic_notifier_chain_register(&panic_notifier_list, &panic_block); |
| 247 | watchdog_task = kthread_run(watchdog, NULL, "khungtaskd"); |
| 248 | |
| 249 | return 0; |
| 250 | } |
| 251 | subsys_initcall(hung_task_init); |