问题
localhost login: [ 806.599439 ] [drm:drm_atomic_helper_wait_for_dependencies [drm_kms_helper]] *ERROR* [CRTC:37:crtc-0] flip_done timed out
[1152.175734] NMI watchdog: BUG: soft lockup -CPU#1 stuck for 23s！[grep:5245]
[1287.825099] [drm:drm_atomic_helper_wait_for_depencies [drm_ks_helper]] * ERROR* [PLANE:33:plane-0] flip_done timed out
解决方案摘自：https://blog.csdn.net/sunny05296/article/details/82858071
最近碰到了Centos7.2上终端打印soft lockup CPU死锁，终端敲命令响应非常慢，系统接近无响应状态。
网上找资料分析了一下原因，直接原因是：如果CPU太忙导致喂狗（watchdog）不及时，此时系统会打印CPU死锁信息：
kernel:BUG: soft lockup - CPU#0 stuck for 38s! [kworker/0:1:25758]
kernel:BUG: soft lockup - CPU#7 stuck for 36s! [java:16182]
......
内核参数kernel.watchdog_thresh（/proc/sys/kernel/watchdog_thresh）系统默认值为10。如果超过2*10秒会打印信息，注意：调整值时参数不能大于60。
虽然调整该值可以延长喂狗等待时间，但是不能彻底解决问题，只能导致信息延迟打印。因此问题的解决，还是需要找到根本原因。
可以打开panic，将/proc/sys/kernel/panic的默认值0改为1，便于定位。
网上查找资料，发现引发CPU死锁的原因有很多种：
* 服务器电源供电不足，导致CPU电压不稳导致CPU死锁
https://ubuntuforums.org/showthread.php?t=2205211
I bought a small (500W) new power supply made by what I feel is a reputable company and made the swap.
GREAT NEWS: After replacing the power supply, the crashes completely stopped!
I wanted to wait a while just to be sure, but it is now a few weeks since the new powersupply went in, and I haven't had a single crash since.
The power supply is not something that I would normally worry about, but in this case it totally fixed my problem.
Thanks to those who read my post, and especially to those who responded.
* vcpus超过物理cpu cores
https://unix.stackexchange.com/questions/70377/bug-soft-lockup-cpu-stuck-for-x-seconds
* 虚机所在的宿主机的CPU太忙或磁盘IO太高
* 虚机的的CPU太忙或磁盘IO太高
https://www.centos.org/forums/viewtopic.php?t=60087
* BIOS KVM开启以后的相关bug，关闭KVM可解决，但关闭以后物理机不支持虚拟化
https://unix.stackexchange.com/questions/70377/bug-soft-lockup-cpu-stuck-for-x-seconds
* VM网卡驱动存在bug，处理高水位流量时存在bug导致CPU死锁
* BIOS开启了超频，导致超频时电压不稳，容易出现CPU死锁
https://ubuntuforums.org/showthread.php?t=2205211
* Linux kernel存在bug
https://unix.stackexchange.com/questions/70377/bug-soft-lockup-cpu-stuck-for-x-seconds
* KVM存在bug
https://unix.stackexchange.com/questions/70377/bug-soft-lockup-cpu-stuck-for-x-seconds
* clocksource tsc unstable on CentOS and cloud Linux with Hyper-V Virtualisation
https://unix.stackexchange.com/questions/70377/bug-soft-lockup-cpu-stuck-for-x-seconds
通过设置clocksource=jiffies可解决
* BIOS Intel C-State开启导致，关闭可解决
https://unix.stackexchange.com/questions/70377/bug-soft-lockup-cpu-stuck-for-x-seconds
https://support.citrix.com/article/CTX127395
http://blog.sina.com.cn/s/blog_906d892d0102vn26.html
* BIOS spread spectrum开启导致
当主板上的时钟震荡发生器工作时，脉冲的尖峰会产生emi（电磁干扰）。spread spectrum（频展）设定功能可以降低脉冲发生器所产生的电磁干扰，脉冲波的尖峰会衰减为较为平滑的曲线。
如果我们没有遇到电磁干扰问题，建议将此项设定为disabled，这栏可以优化系统的性能表现和稳定性；
否则应该将此项设定为enabled。 如果对cpu进行超频，必须将此项禁用。因为即使是微小的脉冲值漂移也会导致超频运行的cpu锁死。
再次强调：CPU超频时，SPREAD SPECTRUM必须关闭，否则容易出现锁死cpu的情况。