本文主要是介绍内核检测soft lockup事件特性，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
前面我已经介绍过 Linux内核故障分类和排查 这篇文章。
通过前文，可以知道内核故障中有一类，叫做lockup，实际上就是死锁，分为soft lockup和hard lockup，对于hard lockup可能还需要平台的支持，那么本文就来模拟触发一下lockup的场景。在开始之前，需要做一下准备工作，编译内核，一定要打开如下的选项：
CONFIG_LOCKUP_DETECTOR=y
CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC=y
CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE=1废话不多说，直接上代码：
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/errno.h>
#include <linux/spinlock.h>
#include <asm-generic/delay.h>
#include <linux/kthread.h>static int soft_lockup = 1;
module_param(soft_lockup, int, 0644);
MODULE_PARM_DESC(soft_lockup, "soft_lockup");static struct task_struct *taskid;
static spinlock_t slock;static int kthread_lockup(void *data)
{spinlock_t *lock;lock = (spinlock_t *)data;while(!kthread_should_stop()) {udelay(19000);if (soft_lockup) {spin_lock(lock);spin_lock(lock);} else {spin_lock_irq(lock); //disable local irqspin_lock_irq(lock);}}return 0;
}static int __init lockup_init(void)
{int err;spin_lock_init(&slock);taskid = kthread_run(kthread_lockup, &slock, "lockup_test");if (IS_ERR(taskid)) {err = PTR_ERR(taskid);return err;}return 0;
}static void __init lockup_exit(void)
{kthread_stop(taskid);
}module_init(lockup_init);
module_exit(lockup_exit);
MODULE_AUTHOR("Haocheng Xie");
MODULE_LICENSE("GPL v2");
这是一个简短的内核测试模块，中间我们会获取两次spinlock来触发死锁行为，第一次spin_lock会关闭本地CPU上的抢占功能，这样在该CPU上就无法产生调度行为。第二次spin_lock就会一直在该CPU上忙等待占用CPU，这样就导致了该CPU一直处于忙等待状态，虽然可以继续处理中断，但是进程却无法切换调度，所以watchdog内核线程也就无法定期喂狗，最后触发panic。
当soft lockup时间超时之后，直接触发panic行为：
/ # NMI watchdog: BUG: soft lockup - CPU#1 stuck for 23s! [lockup_test:646]
Modules linked in: lockup(O)CPU: 1 PID: 646 Comm: lockup_test Tainted: G O 4.0.0 #1
Hardware name: linux,dummy-virt (DT)
task: ffff800078659600 ti: ffff8000787d4000 task.ti: ffff8000787d4000
PC is at _raw_spin_lock+0x38/0x48
LR is at kthread_lockup+0x48/0x80 [lockup]
pc : [<ffff800000562ba0>] lr : [<ffff7ffffc000048>] pstate: 20000145
sp : ffff8000787d7e10
x29: ffff8000787d7e10 x28: 0000000000000000
x27: 0000000000000000 x26: 0000000000000000
x25: 0000000000000000 x24: 0000000000000000
x23: ffff7ffffc000000 x22: ffff7ffffc0002d8
x21: ffff8000006bb4a8 x20: ffff7ffffc0000e4
x19: ffff7ffffc0002d8 x18: 0000000000000004
x17: 0000000000000190 x16: 0000000000100100
x15: 0000000000200200 x14: 00000000000c8000
x13: 0000000000001e12 x12: 0000000000001e12
x11: ffffffffffffffff x10: 00000000000003ff
x9 : ffff8000787d7db0 x8 : ffff800078659b70
x7 : 00000004d70b0640 x6 : 000000007e83e000
x5 : 0000000000000000 x4 : 0000000000800000
x3 : 0000000000000000 x2 : 0000000000000001
x1 : 0000000000010000 x0 : ffff7ffffc0002d8Kernel panic - not syncing: softlockup: hung tasks
CPU: 1 PID: 646 Comm: lockup_test Tainted: G O L 4.0.0 #1
Hardware name: linux,dummy-virt (DT)
Call trace:
[<ffff8000000898fc>] dump_backtrace+0x0/0x11c
[<ffff800000089a28>] show_stack+0x10/0x1c
[<ffff80000055ea74>] dump_stack+0x84/0xc4
[<ffff80000055db50>] panic+0xe0/0x220
[<ffff800000125578>] watchdog_timer_fn+0x224/0x228
[<ffff8000000fca48>] __run_hrtimer.isra.34+0x48/0x108
[<ffff8000000fcd48>] hrtimer_interrupt+0xc8/0x244
[<ffff8000004764ec>] arch_timer_handler_virt+0x28/0x38
[<ffff8000000f0564>] handle_percpu_devid_irq+0x78/0xa0
[<ffff8000000ec614>] generic_handle_irq+0x30/0x4c
[<ffff8000000ec928>] __handle_domain_irq+0x58/0xb0
[<ffff800000082424>] gic_handle_irq+0x30/0x80可以看到上面的打印：
BUG: soft lockup - CPU#1 stuck for 23s! [lockup_test:646]
说明这是一个soft lockup的bug导致的内核崩溃。
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