Linux内核调试技术 - 进程上下文R状态死锁监测模板

Linux内核调试技术——进程上下文R

状态死锁监测

一、lockup detector机制分析

lockup detector机制在内核代码的kernel/watchdog.c中实现，本文以Linux 4.1.15版本源码为例进行分析。首先了解其背后的设计原理：利用进程上下文、中断、nmi中断的不同优先级实现死锁监测。它们3者的优先级关系为“进程上下文 < 中断 < nmi中断”，其中进程上下文优先级最低，可通过中断来进行监测进程的运行状态，nmi中断的优先级最高，它是一种不可屏蔽的中断，在中断上下文中发生死锁时，nmi中断处理也可正常进入，因此可用来监测中断中的死锁。不过可惜的是目前绝大多数的arm32芯片都不支持nmi中断，也包括我手中树莓派的bcm2835芯片。从程序的命名中就可以看出，该程序其实实现了一种软看门狗的功能，下面给出整体的软件流程框图：

该程序为每个cpu创建了一个进程和一个高精度定时器，其中进程用来喂狗，定时器用来唤醒喂狗进程和检测是否存在死锁进程，在检测到死锁进程后就触发报警，接下来详细分析源代码：

[cpp] view plain copy 在CODE上查看代码片派生到我的代码片 void __init lockup_detector_init(void) {

set_sample_period();

if (watchdog_enabled)

watchdog_enable_all_cpus(); }

首先入口函数lockup_detector_init()，该函数会在内核启动流程中按如下路径调用：start_kernel() --> rest_init() --> kernel_init()（启内核线程）--> kernel_init_freeable() --> lockup_detector_init()。该函数首先计算高精度定时器的到期时间（即喂狗时间），该值为监测超时时间值的1/5，默认为4s（20s/5），然后判断开关标识来确定是否启用监测机制，该标识在没有启用hard lockup detect的情况下默认为SOFT_WATCHDOG_ENABLED，表示开

启soft lockup detect。于此同时内核也提供了如下的__setup接口，可从内核启动参数cmd line中设置值和开关：

[cpp] view plain copy 在CODE上查看代码片派生到我的代码片 static int __init softlockup_panic_setup(char *str) {

softlockup_panic = simple_strtoul(str, NULL, 0);

return 1; }

__setup(\

static int __init nowatchdog_setup(char *str) {

watchdog_enabled = 0; return 1; }

__setup(\

static int __init nosoftlockup_setup(char *str) {

watchdog_enabled &= ~SOFT_WATCHDOG_ENABLED; return 1; }

__setup(\

此处假定开启soft lockup detect，接下来调用watchdog_enable_all_cpus()函数，该函数会尝试为每个CPU创建一个喂狗任务（并不会立即启动主函数执行）： [cpp] view plain copy 在CODE上查看代码片派生到我的代码片 static int watchdog_enable_all_cpus(void) {

int err = 0;

if (!watchdog_running) {

err = smpboot_register_percpu_thread(&watchdog_threads); if (err)

pr_err(\ else

watchdog_running = 1; } else { /*

* Enable/disable the lockup detectors or * change the sample period 'on the fly'. */

update_watchdog_all_cpus(); }

return err; }

该函数首先判断是否已经启动了任务，若没有则调用smpboot_register_percpu_thread()函数来创建任务，否则则调用update_watchdog_all_cpus()函数来更新定时器的到期时间。首先分析前一个分支，看一下watchdog_threads结构体的实现：

[cpp] view plain copy 在CODE上查看代码片派生到我的代码片 static struct smp_hotplug_thread watchdog_threads = { .store = &softlockup_watchdog, .thread_should_run = watchdog_should_run, .thread_fn = watchdog,

.thread_comm = \ .setup = watchdog_enable, .cleanup = watchdog_cleanup, .park = watchdog_disable, .unpark = watchdog_enable, };

该结构注册了许多的回调函数，先简单了解一下：（1）softlockup_watchdog是一个全局的per cpu指针，它用来保存创建任务的进程描述符task_struct结构；（2）watchdog_should_run()是任务运行的判断函数，它会判断进程是否需要调用thread_fn指针指向的函数运行；（3）watchdog()是任务运行的主函数，该函数实现线程喂狗的动作；（4）setup回调函数watchdog_enable会在任务首次启动时调用，该函数会创建高精度定时器，用来激活喂狗任务和监测死锁超时；（5）cleanup回调函数用来清除任务，它会关闭定时器；（6）最后的park和unpark回调函数用于暂停运行和恢复运行任务。（7）thread_comm是任务名字，cpu0是watchdog/0，cpu1是watchdog/1，以此类推。

下面来简单看一下smpboot_register_percpu_thread()函数是如何为每个cpu创建任务的，同时又在何处调用上述的那些回调函数的（kernel/smpboot.c）：

[cpp] view plain copy 在CODE上查看代码片派生到我的代码片

int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread) {

unsigned int cpu; int ret = 0;

get_online_cpus();

mutex_lock(&smpboot_threads_lock); for_each_online_cpu(cpu) {

ret = __smpboot_create_thread(plug_thread, cpu); if (ret) {

smpboot_destroy_threads(plug_thread); goto out; }

smpboot_unpark_thread(plug_thread, cpu); }

list_add(&plug_thread->list, &hotplug_threads);

out:

mutex_unlock(&smpboot_threads_lock); put_online_cpus(); return ret; }

EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);

函数遍历所有的online cpu然后为其创建指定的任务，然后将他们添加到hotplug_threads中去（该链表是用来遍历用的）；

[cpp] view plain copy 在CODE上查看代码片派生到我的代码片 static int

__smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu) {

struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); ......

tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu, ht->thread_comm); ......

return 0; }

可以看出，为每个cpu创建的任务并不是直接调用前文中注册的thread_fn()回调函数，而是调用了smpboot_thread_fn()函数，该函数会维护任务运行的几个状态，视状态的不同调用不同的注册回调处理函数：

[cpp] view plain copy 在CODE上查看代码片派生到我的代码片 static int smpboot_thread_fn(void *data) {

struct smpboot_thread_data *td = data; struct smp_hotplug_thread *ht = td->ht;

while (1) {

set_current_state(TASK_INTERRUPTIBLE); preempt_disable();

if (kthread_should_stop()) {

__set_current_state(TASK_RUNNING); preempt_enable(); if (ht->cleanup)

ht->cleanup(td->cpu, cpu_online(td->cpu)); kfree(td); return 0; }

if (kthread_should_park()) {

__set_current_state(TASK_RUNNING);

preempt_enable();

if (ht->park && td->status == HP_THREAD_ACTIVE) { BUG_ON(td->cpu != smp_processor_id()); ht->park(td->cpu);

td->status = HP_THREAD_PARKED; }

kthread_parkme();

/* We might have been woken for stop */ continue; }

BUG_ON(td->cpu != smp_processor_id());

/* Check for state change setup */ switch (td->status) {

case HP_THREAD_NONE:

__set_current_state(TASK_RUNNING); preempt_enable(); if (ht->setup)

ht->setup(td->cpu);

td->status = HP_THREAD_ACTIVE; continue;

case HP_THREAD_PARKED:

__set_current_state(TASK_RUNNING); preempt_enable(); if (ht->unpark)

ht->unpark(td->cpu);

td->status = HP_THREAD_ACTIVE; continue; }

if (!ht->thread_should_run(td->cpu)) { preempt_enable_no_resched(); schedule(); } else {

__set_current_state(TASK_RUNNING); preempt_enable();

ht->thread_fn(td->cpu); } } }

这个函数是一个大循环，在每次循环中都会首先依次判断是否需要停止本任务、是否需要park本任务，如果是则进行相应的处理，可以看到这里就会调用前文中注册的cleanup()和

park()回调函数；如果不需要stop和park则接下来按照状态机处理，对于初次运行的任务，这里会调用setup()回调进行相应的初始化动作；最后对于在正常运行中的最一般情况下，会调用thread_should_run回调判断是否需要调用注册主函数，视判断的返回值情况调用thread_fn()函数。下面来看前文中注册的setup回调watchdog_enable()： [cpp] view plain copy 在CODE上查看代码片派生到我的代码片 static void watchdog_enable(unsigned int cpu) {

struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);

/* kick off the timer for the hardlockup detector */

hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); hrtimer->function = watchdog_timer_fn;

/* Enable the perf event */ watchdog_nmi_enable(cpu);

/* done here because hrtimer_start can only pin to smp_processor_id() */ hrtimer_start(hrtimer, ns_to_ktime(sample_period), HRTIMER_MODE_REL_PINNED);

/* initialize timestamp */

watchdog_set_prio(SCHED_FIFO, MAX_RT_PRIO - 1); __touch_watchdog(); }

值得注意的是，这个函数是每个online的cpu都会运行的，首先从per cpu变量中获取本cpu的高精度定时器指针hrtimer并初始化之，注册定时器到期调用函数watchdog_timer_fn()，然后启动定时器，指定到期时间就是前文中计算的sample_period(4s)，最后调整当前进程的调度策略为FIFO实时进程并提高优先级，这么做是为了保证本喂狗任务能够以较高的优先级运行，以免无法及时喂狗而出现误报的情况。函数最后调用__touch_watchdog()函数执行首次喂狗动作。

[cpp] view plain copy 在CODE上查看代码片派生到我的代码片 static void __touch_watchdog(void) {

__this_cpu_write(watchdog_touch_ts, get_timestamp()); }

这里的watchdog_touch_ts也是一个per cpu变量，每个cpu维护自己独有的。这里将当前系统计时的时钟值（单位ns）以约等于的形式转换的秒单位的值，然后刷新到watchdog_touch_ts中，以此模拟喂狗的动作。

定时器初始化完成后，接下来smpboot_thread_fn()函数就会调用thread_should_run()回调函数watchdog_should_run()：

[cpp] view plain copy 在CODE上查看代码片派生到我的代码片 static int watchdog_should_run(unsigned int cpu) {

return __this_cpu_read(hrtimer_interrupts) !=

__this_cpu_read(soft_lockup_hrtimer_cnt); }

此处只是比较了两个变量，当这两个变量不相等时才会调用thread_fn()回调，否则将任务设置为TASK_INTERRUPTIBLE状态然后调度（睡眠）。那这两个变量值合适才会不一样呢？下面来分析另外一条路，注意前文中的定时器已经启动了，来看一下sample_period时间到期后的调用函数，这个函数比较长，分段来看：

[cpp] view plain copy 在CODE上查看代码片派生到我的代码片 /* watchdog kicker functions */

static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) {

unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts); struct pt_regs *regs = get_irq_regs(); int duration;

int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;

/* kick the hardlockup detector */ watchdog_interrupt_count();

/* kick the softlockup detector */

wake_up_process(__this_cpu_read(softlockup_watchdog));

/* .. and repeat */

hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));

首先获取最后一次的喂狗时间并保存在touch_ts中，然后调用watchdog_interrupt_count()函数累加hrtimer_interrupts值，显然该值表示的是当前cpu触发定时器中断的次数。

然后尝试唤醒已经睡眠的喂狗线程（注意，由于这里改变了hrtimer_interrupts值，前文中的watchdog_should_run自然就会返回TRUE了，那么就可以执行注册的主函数了）。接着本函数继续注册下一次的定时器到期时间。

[cpp] view plain copy 在CODE上查看代码片派生到我的代码片 if (touch_ts == 0) {

if (unlikely(__this_cpu_read(softlockup_touch_sync))) { /*

* If the time stamp was touched atomically * make sure the scheduler tick is up to date. */

__this_cpu_write(softlockup_touch_sync, false); sched_clock_tick(); }

/* Clear the guest paused flag on watchdog reset */ kvm_check_and_clear_guest_paused(); __touch_watchdog();

return HRTIMER_RESTART; }

这个判断在kgdb的调试中会用到，正常情况下不会进入，不做分析，继续往下： [cpp] view plain copy 在CODE上查看代码片派生到我的代码片 /* check for a softlockup

* This is done by making sure a high priority task is * being scheduled. The task touches the watchdog to * indicate it is getting cpu time. If it hasn't then

* this is a good indication some task is hogging the cpu */

duration = is_softlockup(touch_ts);

这里调用is_softlockup()函数返回当前时刻是否已经超过了“看门狗”的到期时间： [cpp] view plain copy 在CODE上查看代码片派生到我的代码片 static int is_softlockup(unsigned long touch_ts) {

unsigned long now = get_timestamp();

if (watchdog_enabled & SOFT_WATCHDOG_ENABLED) { /* Warn about unreasonable delays. */

if (time_after(now, touch_ts + get_softlockup_thresh())) return now - touch_ts; }

return 0; }

这里首先判断是否开启了soft lockup detect，是且已经超时的情况下（默认的超时时间是20s）返回超时时间间隔，否则返回0。下面来看一下超时的情况下会执行哪些处理： [cpp] view plain copy 在CODE上查看代码片派生到我的代码片 if (unlikely(duration)) { ......

/* only warn once */

if (__this_cpu_read(soft_watchdog_warn) == true) { /*

* When multiple processes are causing softlockups the * softlockup detector only warns on the first one * because the code relies on a full quiet cycle to

* re-arm. The second process prevents the quiet cycle * and never gets reported. Use task pointers to detect * this. */

if (__this_cpu_read(softlockup_task_ptr_saved) != current) {

__this_cpu_write(soft_watchdog_warn, false); __touch_watchdog(); }

return HRTIMER_RESTART; }

soft_watchdog_warn标识会在已经出现了一次看门狗超时的情况下置位，此处的用意是对于同一个死锁进程，内核只做一次报警动作，如果死锁的进程发生了改变，那该标识会重新设置为false，将可以重新触发报警。

[cpp] view plain copy 在CODE上查看代码片派生到我的代码片 if (softlockup_all_cpu_backtrace) {

/* Prevent multiple soft-lockup reports if one cpu is already * engaged in dumping cpu back traces */

if (test_and_set_bit(0, &soft_lockup_nmi_warn)) { /* Someone else will report us. Let's give up */ __this_cpu_write(soft_watchdog_warn, true); return HRTIMER_RESTART; } }

softlockup_all_cpu_backtrace是一个开关，用来表示是否需要在一个cpu超时时打印所有cpu的backtrace信息，可以通过sysctrl进行控制。此处的用以是为了避免多个cpu再检测到死锁是同时调用trigger_allbutself_cpu_backtrace函数打印所有cpu的backtrace信息，因为在同一时刻只需要调用一次就可以了。

[cpp] view plain copy 在CODE上查看代码片派生到我的代码片 pr_emerg(\ smp_processor_id(), durwww.sm136.comation, current->comm, task_pid_nr(current));

__this_cpu_write(softlockup_task_ptr_saved, current); print_modules();

print_irqtrace_events(current); if (regs)

show_regs(regs); else

dump_stack();

这里就开始依次打印出内核模块信息，中断信息，中断栈信息和backtrace信息，然后记录下了触发死锁的任务描述符task_struct。

[cpp] view plain copy 在CODE上查看代码片派生到我的代码片 if (softlockup_all_cpu_backtrace) {

/* Avoid generating two back traces for current * given that one is already made above */

trigger_allbutself_cpu_backtrace();

clear_bit(0, &soft_lockup_nmi_warn); /* Barrier to sync with other cpus */ smp_mb__after_atomic(); }

这里同前面相呼应，调用trigger_allbutself_cpu_backtrace()函数打印出了所有cpu的backtrace信息，这个函数是arch架构相关的。

[cpp] view plain copy 在CODE上查看代码片派生到我的代码片 add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK); if (softlockup_panic)

panic(\

__this_cpu_write(soft_watchdog_warn, true);

最后如果设置了panic标识，则直接触发panic，否则置位了报警标识，后续针对触发本次报警的死锁任务将不再报警。分析完超时的处理方式，回过头分析一下前文中的喂狗进程是如何运行的。

[cpp] view plain copy 在CODE上查看代码片派生到我的代码片 static void watchdog(unsigned int cpu) {

__this_cpu_write(soft_lockup_hrtimer_cnt,

__this_cpu_read(hrtimer_interrupts)); __touch_watchdog();

/*

* watchdog_nmi_enable() clears the NMI_WATCHDOG_ENABLED bit in the * failure path. Check for failures that can occur asynchronously - * for example, when CPUs are on-lined - and shut down the hardware * perf event on each CPU accordingly. *

* The only non-obvious place this bit can be cleared is through

* watchdog_nmi_enable(), so a pr_info() is placed there. Placing a

* pr_info here would be too noisy awww.tt951.coms it would result in a message * every few seconds if the hardlockup was disabled but the softlockup * enabled. */

if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED)) watchdog_nmi_disable(cpu); }

这里首先将hrtimer_interrupts的值付给soft_lockup_hrtimer_cnt，这样在本次喂狗结束后到下一次定时器到期前，该函数不会投入运行，进程将进入睡眠状态。该函数剩下的就很简单了，直接调用__touch_watchdog()函数执行喂狗动作。

以上就是进程上下文中的R状态死锁的核心监测代码，该程序还提供了一些可以通过sysctrl控制启停和超时时间等的接口，比较简单就不分析了。从以上实现可以看出其本质就是利用了hr定时器中断处理函数周期性的唤醒进程执行软喂狗动作，同时自身则检测软看门狗是否超时。在正常的情况下，当前cpu的定时器中唤醒的喂狗进程一定是能够得到调度的（视cpu负荷情况可能略有延时），即是不可能超过设定的超时时间的，但是如果当前cpu中的某一个进程占用cpu时间超过了设定的超时时间（20s），就会直接导致软看门狗超时并触发一次报警动作，如果这个进程一直不释放cpu（例如while循环），那么也只会报警一次，反之会重新开启报警功能。

二、示例演示

演示环境：树莓派b（Linux 4.1.15） 1、首先确认启用内核配置 Kernel hacking --->

Debug Lockups and Hangs --->

[*] Detect Hard and Soft Lockups

[*] Panic (Reboot) On Soft Lockups（可选） 2、然后确认内核调度策略配置 Kernel Features --->

Preemption Model (Voluntary Kernel Preemption (Desktop))

( ) No Forced Prenc630.comemption (Server) (X) Voluntary Kernel Preemption (Desktop) ( ) Preemptible Kernel (Low-Latency Desktop)

注意调度策略需要配置为非抢占式的内核，若是抢占式的，则测试程序会无效（因为其他内核进程可能会主动抢占死锁的进程）。 3、编写演示程序

[cpp] view plain copy 在CODE上查看代码片派生到我的代码片 #include #include #include

static int __init rlock_init(void) {

while(1);

return 0; }

static void __exit rlock_exit(void) {

return; }

module_init(rlock_init); module_exit(rlock_exit);

MODULE_LICENSE(\

本程序非常的简单，编写一个模块程序并在模块初始化函数中执行while(1)循环即可，以此来触发insmod进程在rlock_init()函数中陷入R状态死锁。

在树莓派中加载该模块后直接中断就”挂死“了，然后再约20s后内核打印如下： root@apple:~# insmod rlock.ko

[ 60.254450] NMI watchdog: BUG: soft lockup - CPU#0 stuck for 23s! [insmod:515]

[ 60.261684] Modules linked in: rlock(O+) sg bcm2835_gpiomem bcm2835_wdt(O) uio_pdrv_genirq uio

[ 60.270344] CPU: 0 PID: 515 Comm: insmod Tainted: G O 4.1.15 #8 [ 60.277382] Hardware name: BCM2708

[ 60.280783] task: c591df60 ti: c5eaa000 task.ti: c5eaa000 [ 60.286189] PC is at rlock_init+0xc/0x10 [rlock] [ 60.290812] LR is at do_one_initcall+0x90/0x1e8

[ 60.295342] pc : [] lr : [] psr: 60000013 [ 60.295342] sp : c5eabdc8 ip : c5eabdd8 fp : c5eabdd4 [ 60.306803] r10: 00000000 r9 : 00000124 r8 : bf02e000

[ 60.312020] r7 : bf02c0a4 r6 : c5eed660 r5 : c0bbd6e8 r4 : c0bbd6e8 [ 60.318539] r3 : 00000000 r2 : c6c01f00 r1 : 60000013 r0 : 60000013

[ 60.325058] Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user [ 60.332183] Control: 00c5387d Table: 05828008 DAC: 00000015

[ 60.337924] CPU: 0 PID: 515 Comm: insmod Tainted: G O 4.1.15 #8 [ 60.344958] Hardware name: BCM2708

[ 60.348410] [] (unwind_backtrace) from [] (show_stack+0x20/0x24) [ 60.356168] [] (show_stack) from [] (dump_stack+0x20/0x28) [ 60.363398] [] (dump_stack) from [] (show_regs+0x1c/0x20) [ 60.370547] [] (show_regs) from [] (watchdog_timer_fn+0x160/0x1a4) [ 60.378482] [] (watchdog_timer_fn) from [] (__run_hrtimer+0x68/0x1c4) [ 60.386668] [] (__run_hrtimer) from [] (hrtimer_interrupt+0x104/0x270) [ 60.394942] [] (hrtimer_interrupt) from [] (bcm2708_timer_interrupt+0x38/0x48)

[ 60.403911] [] (bcm2708_timer_interrupt) from [] (handle_irq_event_percpu+0x5c/0x200)

[ 60.413481] [] (handle_irq_event_percpu) from [] (handle_irq_event+0x38/0x48) [ 60.422359] [] (handle_irq_event) from [] (handle_level_irq+0x98/0x114) [ 60.430712] [] (handle_level_irq) from [] (__handle_domain_irq+0x7c/0xdc)

[ 60.439244] [] (__handle_domain_irq) from [] (handle_IRQ+0x2c/0x30)

[ 60.447251] [] (handle_IRQ) from [] (asm_do_IRQ+0x18/0x1c) [ 60.454485] [] (asm_do_IRQ) from [] (__irq_svc+0x38/0xb0) [ 60.461613] Exception stack(0xc5eabd80 to 0xc5eabdc8)

[ 60.466670] bd80: 60000013 60000013 c6c01f00 00000000 c0bbd6e8 c0bbd6e8 c5eed660 bf02c0a4

[ 60.474845] bda0: bf02e000 00000124 00000000 c5eabdd4 c5eabdd8 c5eabdc8 c0009558 bf02e00c

[ 60.483010] bdc0: 60000013 ffffffff

[ 60.486515] [] (__irq_svc) from [] (rlock_init+0xc/0x10 [rlock]) [ 60.494271] [] (rlock_init [rlock]) from [] (do_one_initcall+0x90/0x1e8)

[ 60.502721] [] (do_one_initcall) from [] (do_init_module+0x6c/0x1c0) [ 60.510819] [] (do_init_module) from [] (load_module+0x1690/0x1d34) [ 60.518827] [] (load_module) from [] (SyS_init_module+0xdc/0x130) [ 60.526662] [] (SyS_init_module) from [] (ret_fast_syscall+0x0/0x54)

[ 60.534745] Kernel panic - not syncing: softlockup: hung tasks

[ 60.540577] CPU: 0 PID: 515 Comm: insmod Tainted: G O L 4.1.15 #8 [ 60.547613] Hardware name: BCM2708

[ 60.551033] [] (unwind_backtrace) from [] (show_stack+0x20/0x24) [ 60.558781] [] (show_stack) from [] (dump_stack+0x20/0x28) [ 60.566005] [] (dump_stack) from [] (panic+0x90/0x1fc)

[ 60.572885] [] (panic) from [] (watchdog_timer_fn+0x188/0x1a4) [ 60.580464] [] (watchdog_timer_fn) from [] (__run_hrtimer+0x68/0x1c4) [ 60.588648] [] (__run_hrtimer) from [] (hrtimer_interrupt+0x104/0x270) [ 60.596917] [] (hrtimer_interrupt) from [] (bcm2708_timer_interrupt+0x38/0x48)

[ 60.605881] [] (bcm2708_timer_interrupt) from [] (handle_irq_event_percpu+0x5c/0x200)

[ 60.615450] [] (handle_irq_event_percpu) from [] (handle_irq_event+0x38/0x48) [ 60.624326] [] (handle_irq_event) from [] (handle_level_irq+0x98/0x114) [ 60.632680] [] (handle_level_irq) from [] (__handle_domain_irq+0x7c/0xdc)

[ 60.641211] [] (__handle_domain_irq) from [] (handle_IRQ+0x2c/0x30)

[ 60.649218] [] (handle_IRQ) from [] (asm_do_IRQ+0x18/0x1c) [ 60.656450] [] (asm_do_IRQ) from [] (__irq_svc+0x38/0xb0) [ 60.663578] Exception stack(0xc5eabd80 to 0xc5eabdc8)

[ 60.668633] bd80: 60000013 60000013 c6c01f00 00000000 c0bbd6e8 c0bbd6e8 c5eed660 bf02c0a4

[ 60.676806] bda0: bf02e000 00000124 00000000 c5eabdd4 c5eabdd8 c5eabdc8 c0009558 bf02e00c

[ 60.684972] bdc0: 60000013 ffffffff

[ 60.688477] [] (__irq_svc) from [] (rlock_init+0xc/0x10 [rlock]) [ 60.696227] [] (rlock_init [rlock]) from [] (do_one_initcall+0x90/0x1e8) [ 60.704671] [] (do_one_initcall) from [] (do_init_module+0x6c/0x1c0)

[ 60.712765] [] (do_init_module) from [] (load_module+0x1690/0x1d34) [ 60.720771] [] (load_module) from [] (SyS_init_module+0xdc/0x130) [ 60.728607] [] (SyS_init_module) from [] (ret_fast_syscall+0x0/0x54) PANIC: softlockup: hung tasks

三、总结

R状态死锁是在进程上下文或中断上下文中出现的一种长期占用cpu的非正常现象，在不易复现的环境中比较难以定位。本文分析了内核提供的监测其中在进程上下文中死锁的SOFTLOCKUP_DETECTOR机制原理及实现方式。开发人员可通过这种机制较为有效的定位问题。

本文来源：https://www.bwwdw.com/article/6b2a.html