1 /*
2 * Detect Soft Lockups
3 *
4 * started by Ingo Molnar, Copyright (C) 2005, 2006 Red Hat, Inc.
5 *
6 * this code detects soft lockups: incidents in where on a CPU
7 * the kernel does not reschedule for 10 seconds or more.
8 */
9 #include <linux/mm.h>
10 #include <linux/cpu.h>
11 #include <linux/nmi.h>
12 #include <linux/init.h>
13 #include <linux/delay.h>
14 #include <linux/freezer.h>
15 #include <linux/kthread.h>
16 #include <linux/lockdep.h>
17 #include <linux/notifier.h>
18 #include <linux/module.h>
19 #include <linux/sysctl.h>
20
21 #include <asm/irq_regs.h>
22
23 static DEFINE_SPINLOCK(print_lock);
24
25 static DEFINE_PER_CPU(unsigned long, touch_timestamp);
26 static DEFINE_PER_CPU(unsigned long, print_timestamp);
27 static DEFINE_PER_CPU(struct task_struct *, watchdog_task);
28
29 static int __read_mostly did_panic;
30 int __read_mostly softlockup_thresh = 60;
31
32 /*
33 * Should we panic (and reboot, if panic_timeout= is set) when a
34 * soft-lockup occurs:
35 */
36 unsigned int __read_mostly softlockup_panic =
37 CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
38
softlockup_panic_setup(char * str)39 static int __init softlockup_panic_setup(char *str)
40 {
41 softlockup_panic = simple_strtoul(str, NULL, 0);
42
43 return 1;
44 }
45 __setup("softlockup_panic=", softlockup_panic_setup);
46
47 static int
softlock_panic(struct notifier_block * this,unsigned long event,void * ptr)48 softlock_panic(struct notifier_block *this, unsigned long event, void *ptr)
49 {
50 did_panic = 1;
51
52 return NOTIFY_DONE;
53 }
54
55 static struct notifier_block panic_block = {
56 .notifier_call = softlock_panic,
57 };
58
59 /*
60 * Returns seconds, approximately. We don't need nanosecond
61 * resolution, and we don't need to waste time with a big divide when
62 * 2^30ns == 1.074s.
63 */
get_timestamp(int this_cpu)64 static unsigned long get_timestamp(int this_cpu)
65 {
66 return cpu_clock(this_cpu) >> 30LL; /* 2^30 ~= 10^9 */
67 }
68
__touch_softlockup_watchdog(void)69 static void __touch_softlockup_watchdog(void)
70 {
71 int this_cpu = raw_smp_processor_id();
72
73 __raw_get_cpu_var(touch_timestamp) = get_timestamp(this_cpu);
74 }
75
touch_softlockup_watchdog(void)76 void touch_softlockup_watchdog(void)
77 {
78 __raw_get_cpu_var(touch_timestamp) = 0;
79 }
80 EXPORT_SYMBOL(touch_softlockup_watchdog);
81
touch_all_softlockup_watchdogs(void)82 void touch_all_softlockup_watchdogs(void)
83 {
84 int cpu;
85
86 /* Cause each CPU to re-update its timestamp rather than complain */
87 for_each_online_cpu(cpu)
88 per_cpu(touch_timestamp, cpu) = 0;
89 }
90 EXPORT_SYMBOL(touch_all_softlockup_watchdogs);
91
proc_dosoftlockup_thresh(struct ctl_table * table,int write,struct file * filp,void __user * buffer,size_t * lenp,loff_t * ppos)92 int proc_dosoftlockup_thresh(struct ctl_table *table, int write,
93 struct file *filp, void __user *buffer,
94 size_t *lenp, loff_t *ppos)
95 {
96 touch_all_softlockup_watchdogs();
97 return proc_dointvec_minmax(table, write, filp, buffer, lenp, ppos);
98 }
99
100 /*
101 * This callback runs from the timer interrupt, and checks
102 * whether the watchdog thread has hung or not:
103 */
softlockup_tick(void)104 void softlockup_tick(void)
105 {
106 int this_cpu = smp_processor_id();
107 unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu);
108 unsigned long print_timestamp;
109 struct pt_regs *regs = get_irq_regs();
110 unsigned long now;
111
112 /* Is detection switched off? */
113 if (!per_cpu(watchdog_task, this_cpu) || softlockup_thresh <= 0) {
114 /* Be sure we don't false trigger if switched back on */
115 if (touch_timestamp)
116 per_cpu(touch_timestamp, this_cpu) = 0;
117 return;
118 }
119
120 if (touch_timestamp == 0) {
121 __touch_softlockup_watchdog();
122 return;
123 }
124
125 print_timestamp = per_cpu(print_timestamp, this_cpu);
126
127 /* report at most once a second */
128 if (print_timestamp == touch_timestamp || did_panic)
129 return;
130
131 /* do not print during early bootup: */
132 if (unlikely(system_state != SYSTEM_RUNNING)) {
133 __touch_softlockup_watchdog();
134 return;
135 }
136
137 now = get_timestamp(this_cpu);
138
139 /*
140 * Wake up the high-prio watchdog task twice per
141 * threshold timespan.
142 */
143 if (now > touch_timestamp + softlockup_thresh/2)
144 wake_up_process(per_cpu(watchdog_task, this_cpu));
145
146 /* Warn about unreasonable delays: */
147 if (now <= (touch_timestamp + softlockup_thresh))
148 return;
149
150 per_cpu(print_timestamp, this_cpu) = touch_timestamp;
151
152 spin_lock(&print_lock);
153 printk(KERN_ERR "BUG: soft lockup - CPU#%d stuck for %lus! [%s:%d]\n",
154 this_cpu, now - touch_timestamp,
155 current->comm, task_pid_nr(current));
156 print_modules();
157 print_irqtrace_events(current);
158 if (regs)
159 show_regs(regs);
160 else
161 dump_stack();
162 spin_unlock(&print_lock);
163
164 if (softlockup_panic)
165 panic("softlockup: hung tasks");
166 }
167
168 /*
169 * Have a reasonable limit on the number of tasks checked:
170 */
171 unsigned long __read_mostly sysctl_hung_task_check_count = 1024;
172
173 /*
174 * Zero means infinite timeout - no checking done:
175 */
176 unsigned long __read_mostly sysctl_hung_task_timeout_secs = 480;
177
178 unsigned long __read_mostly sysctl_hung_task_warnings = 10;
179
180 /*
181 * Only do the hung-tasks check on one CPU:
182 */
183 static int check_cpu __read_mostly = -1;
184
check_hung_task(struct task_struct * t,unsigned long now)185 static void check_hung_task(struct task_struct *t, unsigned long now)
186 {
187 unsigned long switch_count = t->nvcsw + t->nivcsw;
188
189 if (t->flags & PF_FROZEN)
190 return;
191
192 if (switch_count != t->last_switch_count || !t->last_switch_timestamp) {
193 t->last_switch_count = switch_count;
194 t->last_switch_timestamp = now;
195 return;
196 }
197 if ((long)(now - t->last_switch_timestamp) <
198 sysctl_hung_task_timeout_secs)
199 return;
200 if (!sysctl_hung_task_warnings)
201 return;
202 sysctl_hung_task_warnings--;
203
204 /*
205 * Ok, the task did not get scheduled for more than 2 minutes,
206 * complain:
207 */
208 printk(KERN_ERR "INFO: task %s:%d blocked for more than "
209 "%ld seconds.\n", t->comm, t->pid,
210 sysctl_hung_task_timeout_secs);
211 printk(KERN_ERR "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
212 " disables this message.\n");
213 sched_show_task(t);
214 __debug_show_held_locks(t);
215
216 t->last_switch_timestamp = now;
217 touch_nmi_watchdog();
218
219 if (softlockup_panic)
220 panic("softlockup: blocked tasks");
221 }
222
223 /*
224 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
225 * a really long time (120 seconds). If that happens, print out
226 * a warning.
227 */
check_hung_uninterruptible_tasks(int this_cpu)228 static void check_hung_uninterruptible_tasks(int this_cpu)
229 {
230 int max_count = sysctl_hung_task_check_count;
231 unsigned long now = get_timestamp(this_cpu);
232 struct task_struct *g, *t;
233
234 /*
235 * If the system crashed already then all bets are off,
236 * do not report extra hung tasks:
237 */
238 if (test_taint(TAINT_DIE) || did_panic)
239 return;
240
241 read_lock(&tasklist_lock);
242 do_each_thread(g, t) {
243 if (!--max_count)
244 goto unlock;
245 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
246 if (t->state == TASK_UNINTERRUPTIBLE)
247 check_hung_task(t, now);
248 } while_each_thread(g, t);
249 unlock:
250 read_unlock(&tasklist_lock);
251 }
252
253 /*
254 * The watchdog thread - runs every second and touches the timestamp.
255 */
watchdog(void * __bind_cpu)256 static int watchdog(void *__bind_cpu)
257 {
258 struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
259 int this_cpu = (long)__bind_cpu;
260
261 sched_setscheduler(current, SCHED_FIFO, ¶m);
262
263 /* initialize timestamp */
264 __touch_softlockup_watchdog();
265
266 set_current_state(TASK_INTERRUPTIBLE);
267 /*
268 * Run briefly once per second to reset the softlockup timestamp.
269 * If this gets delayed for more than 60 seconds then the
270 * debug-printout triggers in softlockup_tick().
271 */
272 while (!kthread_should_stop()) {
273 __touch_softlockup_watchdog();
274 schedule();
275
276 if (kthread_should_stop())
277 break;
278
279 if (this_cpu == check_cpu) {
280 if (sysctl_hung_task_timeout_secs)
281 check_hung_uninterruptible_tasks(this_cpu);
282 }
283
284 set_current_state(TASK_INTERRUPTIBLE);
285 }
286 __set_current_state(TASK_RUNNING);
287
288 return 0;
289 }
290
291 /*
292 * Create/destroy watchdog threads as CPUs come and go:
293 */
294 static int __cpuinit
cpu_callback(struct notifier_block * nfb,unsigned long action,void * hcpu)295 cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
296 {
297 int hotcpu = (unsigned long)hcpu;
298 struct task_struct *p;
299
300 switch (action) {
301 case CPU_UP_PREPARE:
302 case CPU_UP_PREPARE_FROZEN:
303 BUG_ON(per_cpu(watchdog_task, hotcpu));
304 p = kthread_create(watchdog, hcpu, "watchdog/%d", hotcpu);
305 if (IS_ERR(p)) {
306 printk(KERN_ERR "watchdog for %i failed\n", hotcpu);
307 return NOTIFY_BAD;
308 }
309 per_cpu(touch_timestamp, hotcpu) = 0;
310 per_cpu(watchdog_task, hotcpu) = p;
311 kthread_bind(p, hotcpu);
312 break;
313 case CPU_ONLINE:
314 case CPU_ONLINE_FROZEN:
315 check_cpu = cpumask_any(cpu_online_mask);
316 wake_up_process(per_cpu(watchdog_task, hotcpu));
317 break;
318 #ifdef CONFIG_HOTPLUG_CPU
319 case CPU_DOWN_PREPARE:
320 case CPU_DOWN_PREPARE_FROZEN:
321 if (hotcpu == check_cpu) {
322 /* Pick any other online cpu. */
323 check_cpu = cpumask_any_but(cpu_online_mask, hotcpu);
324 }
325 break;
326
327 case CPU_UP_CANCELED:
328 case CPU_UP_CANCELED_FROZEN:
329 if (!per_cpu(watchdog_task, hotcpu))
330 break;
331 /* Unbind so it can run. Fall thru. */
332 kthread_bind(per_cpu(watchdog_task, hotcpu),
333 cpumask_any(cpu_online_mask));
334 case CPU_DEAD:
335 case CPU_DEAD_FROZEN:
336 p = per_cpu(watchdog_task, hotcpu);
337 per_cpu(watchdog_task, hotcpu) = NULL;
338 kthread_stop(p);
339 break;
340 #endif /* CONFIG_HOTPLUG_CPU */
341 }
342 return NOTIFY_OK;
343 }
344
345 static struct notifier_block __cpuinitdata cpu_nfb = {
346 .notifier_call = cpu_callback
347 };
348
349 static int __initdata nosoftlockup;
350
nosoftlockup_setup(char * str)351 static int __init nosoftlockup_setup(char *str)
352 {
353 nosoftlockup = 1;
354 return 1;
355 }
356 __setup("nosoftlockup", nosoftlockup_setup);
357
spawn_softlockup_task(void)358 static int __init spawn_softlockup_task(void)
359 {
360 void *cpu = (void *)(long)smp_processor_id();
361 int err;
362
363 if (nosoftlockup)
364 return 0;
365
366 err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
367 if (err == NOTIFY_BAD) {
368 BUG();
369 return 1;
370 }
371 cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
372 register_cpu_notifier(&cpu_nfb);
373
374 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
375
376 return 0;
377 }
378 early_initcall(spawn_softlockup_task);
379