2 * Detect hard and soft lockups on a system
4 * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
6 * Note: Most of this code is borrowed heavily from the original softlockup
7 * detector, so thanks to Ingo for the initial implementation.
8 * Some chunks also taken from the old x86-specific nmi watchdog code, thanks
9 * to those contributors as well.
12 #define pr_fmt(fmt) "watchdog: " fmt
15 #include <linux/cpu.h>
16 #include <linux/nmi.h>
17 #include <linux/init.h>
18 #include <linux/module.h>
19 #include <linux/sysctl.h>
20 #include <linux/smpboot.h>
21 #include <linux/sched/rt.h>
22 #include <uapi/linux/sched/types.h>
23 #include <linux/tick.h>
24 #include <linux/workqueue.h>
25 #include <linux/sched/clock.h>
26 #include <linux/sched/debug.h>
28 #include <asm/irq_regs.h>
29 #include <linux/kvm_para.h>
30 #include <linux/kthread.h>
32 static DEFINE_MUTEX(watchdog_mutex
);
34 int __read_mostly nmi_watchdog_enabled
;
36 #if defined(CONFIG_HARDLOCKUP_DETECTOR) || defined(CONFIG_HAVE_NMI_WATCHDOG)
37 unsigned long __read_mostly watchdog_enabled
= SOFT_WATCHDOG_ENABLED
|
40 unsigned long __read_mostly watchdog_enabled
= SOFT_WATCHDOG_ENABLED
;
43 #ifdef CONFIG_HARDLOCKUP_DETECTOR
45 * Should we panic when a soft-lockup or hard-lockup occurs:
47 unsigned int __read_mostly hardlockup_panic
=
48 CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE
;
50 * We may not want to enable hard lockup detection by default in all cases,
51 * for example when running the kernel as a guest on a hypervisor. In these
52 * cases this function can be called to disable hard lockup detection. This
53 * function should only be executed once by the boot processor before the
54 * kernel command line parameters are parsed, because otherwise it is not
55 * possible to override this in hardlockup_panic_setup().
57 void __init
hardlockup_detector_disable(void)
59 watchdog_enabled
&= ~NMI_WATCHDOG_ENABLED
;
62 static int __init
hardlockup_panic_setup(char *str
)
64 if (!strncmp(str
, "panic", 5))
66 else if (!strncmp(str
, "nopanic", 7))
68 else if (!strncmp(str
, "0", 1))
69 watchdog_enabled
&= ~NMI_WATCHDOG_ENABLED
;
70 else if (!strncmp(str
, "1", 1))
71 watchdog_enabled
|= NMI_WATCHDOG_ENABLED
;
74 __setup("nmi_watchdog=", hardlockup_panic_setup
);
77 int __read_mostly sysctl_hardlockup_all_cpu_backtrace
;
79 static int __init
hardlockup_all_cpu_backtrace_setup(char *str
)
81 sysctl_hardlockup_all_cpu_backtrace
= !!simple_strtol(str
, NULL
, 0);
84 __setup("hardlockup_all_cpu_backtrace=", hardlockup_all_cpu_backtrace_setup
);
85 # endif /* CONFIG_SMP */
86 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
88 int __read_mostly watchdog_user_enabled
;
89 int __read_mostly watchdog_thresh
= 10;
91 struct cpumask watchdog_cpumask __read_mostly
;
92 unsigned long *watchdog_cpumask_bits
= cpumask_bits(&watchdog_cpumask
);
95 * These functions can be overridden if an architecture implements its
96 * own hardlockup detector.
98 * watchdog_nmi_enable/disable can be implemented to start and stop when
99 * softlockup watchdog threads start and stop. The arch must select the
100 * SOFTLOCKUP_DETECTOR Kconfig.
102 int __weak
watchdog_nmi_enable(unsigned int cpu
)
107 void __weak
watchdog_nmi_disable(unsigned int cpu
)
109 hardlockup_detector_perf_disable();
113 * watchdog_nmi_reconfigure can be implemented to be notified after any
114 * watchdog configuration change. The arch hardlockup watchdog should
115 * respond to the following variables:
116 * - nmi_watchdog_enabled
119 * - sysctl_hardlockup_all_cpu_backtrace
122 void __weak
watchdog_nmi_reconfigure(void) { }
124 #ifdef CONFIG_SOFTLOCKUP_DETECTOR
126 /* Global variables, exported for sysctl */
127 unsigned int __read_mostly softlockup_panic
=
128 CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE
;
129 int __read_mostly soft_watchdog_enabled
;
131 struct cpumask watchdog_allowed_mask __read_mostly
;
132 static bool softlockup_threads_initialized __read_mostly
;
134 static u64 __read_mostly sample_period
;
136 static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts
);
137 static DEFINE_PER_CPU(struct task_struct
*, softlockup_watchdog
);
138 static DEFINE_PER_CPU(struct hrtimer
, watchdog_hrtimer
);
139 static DEFINE_PER_CPU(bool, softlockup_touch_sync
);
140 static DEFINE_PER_CPU(bool, soft_watchdog_warn
);
141 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts
);
142 static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt
);
143 static DEFINE_PER_CPU(struct task_struct
*, softlockup_task_ptr_saved
);
144 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved
);
145 static unsigned long soft_lockup_nmi_warn
;
147 static int __init
softlockup_panic_setup(char *str
)
149 softlockup_panic
= simple_strtoul(str
, NULL
, 0);
152 __setup("softlockup_panic=", softlockup_panic_setup
);
154 static int __init
nowatchdog_setup(char *str
)
156 watchdog_enabled
= 0;
159 __setup("nowatchdog", nowatchdog_setup
);
161 static int __init
nosoftlockup_setup(char *str
)
163 watchdog_enabled
&= ~SOFT_WATCHDOG_ENABLED
;
166 __setup("nosoftlockup", nosoftlockup_setup
);
169 int __read_mostly sysctl_softlockup_all_cpu_backtrace
;
171 static int __init
softlockup_all_cpu_backtrace_setup(char *str
)
173 sysctl_softlockup_all_cpu_backtrace
= !!simple_strtol(str
, NULL
, 0);
176 __setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup
);
179 static void __lockup_detector_cleanup(void);
182 * Hard-lockup warnings should be triggered after just a few seconds. Soft-
183 * lockups can have false positives under extreme conditions. So we generally
184 * want a higher threshold for soft lockups than for hard lockups. So we couple
185 * the thresholds with a factor: we make the soft threshold twice the amount of
186 * time the hard threshold is.
188 static int get_softlockup_thresh(void)
190 return watchdog_thresh
* 2;
194 * Returns seconds, approximately. We don't need nanosecond
195 * resolution, and we don't need to waste time with a big divide when
198 static unsigned long get_timestamp(void)
200 return running_clock() >> 30LL; /* 2^30 ~= 10^9 */
203 static void set_sample_period(void)
206 * convert watchdog_thresh from seconds to ns
207 * the divide by 5 is to give hrtimer several chances (two
208 * or three with the current relation between the soft
209 * and hard thresholds) to increment before the
210 * hardlockup detector generates a warning
212 sample_period
= get_softlockup_thresh() * ((u64
)NSEC_PER_SEC
/ 5);
213 watchdog_update_hrtimer_threshold(sample_period
);
216 /* Commands for resetting the watchdog */
217 static void __touch_watchdog(void)
219 __this_cpu_write(watchdog_touch_ts
, get_timestamp());
223 * touch_softlockup_watchdog_sched - touch watchdog on scheduler stalls
225 * Call when the scheduler may have stalled for legitimate reasons
226 * preventing the watchdog task from executing - e.g. the scheduler
227 * entering idle state. This should only be used for scheduler events.
228 * Use touch_softlockup_watchdog() for everything else.
230 void touch_softlockup_watchdog_sched(void)
233 * Preemption can be enabled. It doesn't matter which CPU's timestamp
234 * gets zeroed here, so use the raw_ operation.
236 raw_cpu_write(watchdog_touch_ts
, 0);
239 void touch_softlockup_watchdog(void)
241 touch_softlockup_watchdog_sched();
242 wq_watchdog_touch(raw_smp_processor_id());
244 EXPORT_SYMBOL(touch_softlockup_watchdog
);
246 void touch_all_softlockup_watchdogs(void)
251 * watchdog_mutex cannpt be taken here, as this might be called
252 * from (soft)interrupt context, so the access to
253 * watchdog_allowed_cpumask might race with a concurrent update.
255 * The watchdog time stamp can race against a concurrent real
256 * update as well, the only side effect might be a cycle delay for
257 * the softlockup check.
259 for_each_cpu(cpu
, &watchdog_allowed_mask
)
260 per_cpu(watchdog_touch_ts
, cpu
) = 0;
261 wq_watchdog_touch(-1);
264 void touch_softlockup_watchdog_sync(void)
266 __this_cpu_write(softlockup_touch_sync
, true);
267 __this_cpu_write(watchdog_touch_ts
, 0);
270 static int is_softlockup(unsigned long touch_ts
)
272 unsigned long now
= get_timestamp();
274 if ((watchdog_enabled
& SOFT_WATCHDOG_ENABLED
) && watchdog_thresh
){
275 /* Warn about unreasonable delays. */
276 if (time_after(now
, touch_ts
+ get_softlockup_thresh()))
277 return now
- touch_ts
;
282 /* watchdog detector functions */
283 bool is_hardlockup(void)
285 unsigned long hrint
= __this_cpu_read(hrtimer_interrupts
);
287 if (__this_cpu_read(hrtimer_interrupts_saved
) == hrint
)
290 __this_cpu_write(hrtimer_interrupts_saved
, hrint
);
294 static void watchdog_interrupt_count(void)
296 __this_cpu_inc(hrtimer_interrupts
);
299 /* watchdog kicker functions */
300 static enum hrtimer_restart
watchdog_timer_fn(struct hrtimer
*hrtimer
)
302 unsigned long touch_ts
= __this_cpu_read(watchdog_touch_ts
);
303 struct pt_regs
*regs
= get_irq_regs();
305 int softlockup_all_cpu_backtrace
= sysctl_softlockup_all_cpu_backtrace
;
307 if (!watchdog_enabled
)
308 return HRTIMER_NORESTART
;
310 /* kick the hardlockup detector */
311 watchdog_interrupt_count();
313 /* kick the softlockup detector */
314 wake_up_process(__this_cpu_read(softlockup_watchdog
));
317 hrtimer_forward_now(hrtimer
, ns_to_ktime(sample_period
));
320 if (unlikely(__this_cpu_read(softlockup_touch_sync
))) {
322 * If the time stamp was touched atomically
323 * make sure the scheduler tick is up to date.
325 __this_cpu_write(softlockup_touch_sync
, false);
329 /* Clear the guest paused flag on watchdog reset */
330 kvm_check_and_clear_guest_paused();
332 return HRTIMER_RESTART
;
335 /* check for a softlockup
336 * This is done by making sure a high priority task is
337 * being scheduled. The task touches the watchdog to
338 * indicate it is getting cpu time. If it hasn't then
339 * this is a good indication some task is hogging the cpu
341 duration
= is_softlockup(touch_ts
);
342 if (unlikely(duration
)) {
344 * If a virtual machine is stopped by the host it can look to
345 * the watchdog like a soft lockup, check to see if the host
346 * stopped the vm before we issue the warning
348 if (kvm_check_and_clear_guest_paused())
349 return HRTIMER_RESTART
;
352 if (__this_cpu_read(soft_watchdog_warn
) == true) {
354 * When multiple processes are causing softlockups the
355 * softlockup detector only warns on the first one
356 * because the code relies on a full quiet cycle to
357 * re-arm. The second process prevents the quiet cycle
358 * and never gets reported. Use task pointers to detect
361 if (__this_cpu_read(softlockup_task_ptr_saved
) !=
363 __this_cpu_write(soft_watchdog_warn
, false);
366 return HRTIMER_RESTART
;
369 if (softlockup_all_cpu_backtrace
) {
370 /* Prevent multiple soft-lockup reports if one cpu is already
371 * engaged in dumping cpu back traces
373 if (test_and_set_bit(0, &soft_lockup_nmi_warn
)) {
374 /* Someone else will report us. Let's give up */
375 __this_cpu_write(soft_watchdog_warn
, true);
376 return HRTIMER_RESTART
;
380 pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
381 smp_processor_id(), duration
,
382 current
->comm
, task_pid_nr(current
));
383 __this_cpu_write(softlockup_task_ptr_saved
, current
);
385 print_irqtrace_events(current
);
391 if (softlockup_all_cpu_backtrace
) {
392 /* Avoid generating two back traces for current
393 * given that one is already made above
395 trigger_allbutself_cpu_backtrace();
397 clear_bit(0, &soft_lockup_nmi_warn
);
398 /* Barrier to sync with other cpus */
399 smp_mb__after_atomic();
402 add_taint(TAINT_SOFTLOCKUP
, LOCKDEP_STILL_OK
);
403 if (softlockup_panic
)
404 panic("softlockup: hung tasks");
405 __this_cpu_write(soft_watchdog_warn
, true);
407 __this_cpu_write(soft_watchdog_warn
, false);
409 return HRTIMER_RESTART
;
412 static void watchdog_set_prio(unsigned int policy
, unsigned int prio
)
414 struct sched_param param
= { .sched_priority
= prio
};
416 sched_setscheduler(current
, policy
, ¶m
);
419 static void watchdog_enable(unsigned int cpu
)
421 struct hrtimer
*hrtimer
= this_cpu_ptr(&watchdog_hrtimer
);
424 * Start the timer first to prevent the NMI watchdog triggering
425 * before the timer has a chance to fire.
427 hrtimer_init(hrtimer
, CLOCK_MONOTONIC
, HRTIMER_MODE_REL
);
428 hrtimer
->function
= watchdog_timer_fn
;
429 hrtimer_start(hrtimer
, ns_to_ktime(sample_period
),
430 HRTIMER_MODE_REL_PINNED
);
432 /* Initialize timestamp */
434 /* Enable the perf event */
435 watchdog_nmi_enable(cpu
);
437 watchdog_set_prio(SCHED_FIFO
, MAX_RT_PRIO
- 1);
440 static void watchdog_disable(unsigned int cpu
)
442 struct hrtimer
*hrtimer
= this_cpu_ptr(&watchdog_hrtimer
);
444 watchdog_set_prio(SCHED_NORMAL
, 0);
446 * Disable the perf event first. That prevents that a large delay
447 * between disabling the timer and disabling the perf event causes
448 * the perf NMI to detect a false positive.
450 watchdog_nmi_disable(cpu
);
451 hrtimer_cancel(hrtimer
);
454 static void watchdog_cleanup(unsigned int cpu
, bool online
)
456 watchdog_disable(cpu
);
459 static int watchdog_should_run(unsigned int cpu
)
461 return __this_cpu_read(hrtimer_interrupts
) !=
462 __this_cpu_read(soft_lockup_hrtimer_cnt
);
466 * The watchdog thread function - touches the timestamp.
468 * It only runs once every sample_period seconds (4 seconds by
469 * default) to reset the softlockup timestamp. If this gets delayed
470 * for more than 2*watchdog_thresh seconds then the debug-printout
471 * triggers in watchdog_timer_fn().
473 static void watchdog(unsigned int cpu
)
475 __this_cpu_write(soft_lockup_hrtimer_cnt
,
476 __this_cpu_read(hrtimer_interrupts
));
480 static struct smp_hotplug_thread watchdog_threads
= {
481 .store
= &softlockup_watchdog
,
482 .thread_should_run
= watchdog_should_run
,
483 .thread_fn
= watchdog
,
484 .thread_comm
= "watchdog/%u",
485 .setup
= watchdog_enable
,
486 .cleanup
= watchdog_cleanup
,
487 .park
= watchdog_disable
,
488 .unpark
= watchdog_enable
,
491 static void softlockup_update_smpboot_threads(void)
493 lockdep_assert_held(&watchdog_mutex
);
495 if (!softlockup_threads_initialized
)
498 smpboot_update_cpumask_percpu_thread(&watchdog_threads
,
499 &watchdog_allowed_mask
);
500 __lockup_detector_cleanup();
503 /* Temporarily park all watchdog threads */
504 static void softlockup_park_all_threads(void)
506 cpumask_clear(&watchdog_allowed_mask
);
507 softlockup_update_smpboot_threads();
510 /* Unpark enabled threads */
511 static void softlockup_unpark_threads(void)
513 cpumask_copy(&watchdog_allowed_mask
, &watchdog_cpumask
);
514 softlockup_update_smpboot_threads();
517 static void softlockup_reconfigure_threads(bool enabled
)
519 softlockup_park_all_threads();
522 softlockup_unpark_threads();
526 * Create the watchdog thread infrastructure.
528 * The threads are not unparked as watchdog_allowed_mask is empty. When
529 * the threads are sucessfully initialized, take the proper locks and
530 * unpark the threads in the watchdog_cpumask if the watchdog is enabled.
532 static __init
void softlockup_init_threads(void)
537 * If sysctl is off and watchdog got disabled on the command line,
538 * nothing to do here.
540 if (!IS_ENABLED(CONFIG_SYSCTL
) &&
541 !(watchdog_enabled
&& watchdog_thresh
))
544 ret
= smpboot_register_percpu_thread_cpumask(&watchdog_threads
,
545 &watchdog_allowed_mask
);
547 pr_err("Failed to initialize soft lockup detector threads\n");
551 mutex_lock(&watchdog_mutex
);
552 softlockup_threads_initialized
= true;
553 softlockup_reconfigure_threads(watchdog_enabled
&& watchdog_thresh
);
554 mutex_unlock(&watchdog_mutex
);
557 #else /* CONFIG_SOFTLOCKUP_DETECTOR */
558 static inline int watchdog_park_threads(void) { return 0; }
559 static inline void watchdog_unpark_threads(void) { }
560 static inline int watchdog_enable_all_cpus(void) { return 0; }
561 static inline void watchdog_disable_all_cpus(void) { }
562 static inline void softlockup_init_threads(void) { }
563 static inline void softlockup_reconfigure_threads(bool enabled
) { }
564 #endif /* !CONFIG_SOFTLOCKUP_DETECTOR */
566 static void __lockup_detector_cleanup(void)
568 lockdep_assert_held(&watchdog_mutex
);
569 hardlockup_detector_perf_cleanup();
573 * lockup_detector_cleanup - Cleanup after cpu hotplug or sysctl changes
575 * Caller must not hold the cpu hotplug rwsem.
577 void lockup_detector_cleanup(void)
579 mutex_lock(&watchdog_mutex
);
580 __lockup_detector_cleanup();
581 mutex_unlock(&watchdog_mutex
);
585 * lockup_detector_soft_poweroff - Interface to stop lockup detector(s)
587 * Special interface for parisc. It prevents lockup detector warnings from
588 * the default pm_poweroff() function which busy loops forever.
590 void lockup_detector_soft_poweroff(void)
592 watchdog_enabled
= 0;
597 /* Propagate any changes to the watchdog threads */
598 static void proc_watchdog_update(void)
600 /* Remove impossible cpus to keep sysctl output clean. */
601 cpumask_and(&watchdog_cpumask
, &watchdog_cpumask
, cpu_possible_mask
);
602 softlockup_reconfigure_threads(watchdog_enabled
&& watchdog_thresh
);
603 watchdog_nmi_reconfigure();
607 * common function for watchdog, nmi_watchdog and soft_watchdog parameter
609 * caller | table->data points to | 'which' contains the flag(s)
610 * -------------------|-----------------------|-----------------------------
611 * proc_watchdog | watchdog_user_enabled | NMI_WATCHDOG_ENABLED or'ed
612 * | | with SOFT_WATCHDOG_ENABLED
613 * -------------------|-----------------------|-----------------------------
614 * proc_nmi_watchdog | nmi_watchdog_enabled | NMI_WATCHDOG_ENABLED
615 * -------------------|-----------------------|-----------------------------
616 * proc_soft_watchdog | soft_watchdog_enabled | SOFT_WATCHDOG_ENABLED
618 static int proc_watchdog_common(int which
, struct ctl_table
*table
, int write
,
619 void __user
*buffer
, size_t *lenp
, loff_t
*ppos
)
622 int *watchdog_param
= (int *)table
->data
;
624 cpu_hotplug_disable();
625 mutex_lock(&watchdog_mutex
);
628 * If the parameter is being read return the state of the corresponding
629 * bit(s) in 'watchdog_enabled', else update 'watchdog_enabled' and the
630 * run state of the lockup detectors.
633 *watchdog_param
= (watchdog_enabled
& which
) != 0;
634 err
= proc_dointvec_minmax(table
, write
, buffer
, lenp
, ppos
);
636 err
= proc_dointvec_minmax(table
, write
, buffer
, lenp
, ppos
);
641 * There is a race window between fetching the current value
642 * from 'watchdog_enabled' and storing the new value. During
643 * this race window, watchdog_nmi_enable() can sneak in and
644 * clear the NMI_WATCHDOG_ENABLED bit in 'watchdog_enabled'.
645 * The 'cmpxchg' detects this race and the loop retries.
648 old
= watchdog_enabled
;
650 * If the parameter value is not zero set the
651 * corresponding bit(s), else clear it(them).
657 } while (cmpxchg(&watchdog_enabled
, old
, new) != old
);
660 proc_watchdog_update();
663 mutex_unlock(&watchdog_mutex
);
664 cpu_hotplug_enable();
669 * /proc/sys/kernel/watchdog
671 int proc_watchdog(struct ctl_table
*table
, int write
,
672 void __user
*buffer
, size_t *lenp
, loff_t
*ppos
)
674 return proc_watchdog_common(NMI_WATCHDOG_ENABLED
|SOFT_WATCHDOG_ENABLED
,
675 table
, write
, buffer
, lenp
, ppos
);
679 * /proc/sys/kernel/nmi_watchdog
681 int proc_nmi_watchdog(struct ctl_table
*table
, int write
,
682 void __user
*buffer
, size_t *lenp
, loff_t
*ppos
)
684 return proc_watchdog_common(NMI_WATCHDOG_ENABLED
,
685 table
, write
, buffer
, lenp
, ppos
);
689 * /proc/sys/kernel/soft_watchdog
691 int proc_soft_watchdog(struct ctl_table
*table
, int write
,
692 void __user
*buffer
, size_t *lenp
, loff_t
*ppos
)
694 return proc_watchdog_common(SOFT_WATCHDOG_ENABLED
,
695 table
, write
, buffer
, lenp
, ppos
);
699 * /proc/sys/kernel/watchdog_thresh
701 int proc_watchdog_thresh(struct ctl_table
*table
, int write
,
702 void __user
*buffer
, size_t *lenp
, loff_t
*ppos
)
706 cpu_hotplug_disable();
707 mutex_lock(&watchdog_mutex
);
709 old
= READ_ONCE(watchdog_thresh
);
710 err
= proc_dointvec_minmax(table
, write
, buffer
, lenp
, ppos
);
712 if (!err
&& write
&& old
!= READ_ONCE(watchdog_thresh
))
713 proc_watchdog_update();
715 mutex_unlock(&watchdog_mutex
);
716 cpu_hotplug_enable();
721 * The cpumask is the mask of possible cpus that the watchdog can run
722 * on, not the mask of cpus it is actually running on. This allows the
723 * user to specify a mask that will include cpus that have not yet
724 * been brought online, if desired.
726 int proc_watchdog_cpumask(struct ctl_table
*table
, int write
,
727 void __user
*buffer
, size_t *lenp
, loff_t
*ppos
)
731 cpu_hotplug_disable();
732 mutex_lock(&watchdog_mutex
);
734 err
= proc_do_large_bitmap(table
, write
, buffer
, lenp
, ppos
);
736 proc_watchdog_update();
738 mutex_unlock(&watchdog_mutex
);
739 cpu_hotplug_enable();
742 #endif /* CONFIG_SYSCTL */
744 void __init
lockup_detector_init(void)
746 #ifdef CONFIG_NO_HZ_FULL
747 if (tick_nohz_full_enabled()) {
748 pr_info("Disabling watchdog on nohz_full cores by default\n");
749 cpumask_copy(&watchdog_cpumask
, housekeeping_mask
);
751 cpumask_copy(&watchdog_cpumask
, cpu_possible_mask
);
753 cpumask_copy(&watchdog_cpumask
, cpu_possible_mask
);
756 softlockup_init_threads();