线上centos6出现软死锁 kernel:BUG: soft lockup

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线上centos6出现软死锁 kernel:BUG: soft lockup
　　今天线上一台centos6机器用xshell一直连接不上，然后在xshell上显示
　　Message from syslogd@GZxxx at Mar 29 14:13:14 ...
kernel:BUG: soft lockup - CPU#1 stuck for 68s! [events/1:36]
　　过了10分钟，终于可以连上了，看一下开机日志
　　
dmesg |grep stuck
BUG: soft lockup - CPU#2 stuck for 67s! [vmmemctl:894]
BUG: soft lockup - CPU#5 stuck for 67s! [bdi-default:49]
BUG: soft lockup - CPU#3 stuck for 67s! [irqbalance:1351]
BUG: soft lockup - CPU#4 stuck for 67s! [swapper:0]
BUG: soft lockup - CPU#6 stuck for 67s! [watchdog/6:30]
BUG: soft lockup - CPU#5 stuck for 67s! [vmmemctl:894]
BUG: soft lockup - CPU#0 stuck for 67s! [events/0:35]
BUG: soft lockup - CPU#7 stuck for 67s! [lldpad:1459]
BUG: soft lockup - CPU#6 stuck for 67s! [mpt_poll_0:376]
BUG: soft lockup - CPU#4 stuck for 67s! [ksoftirqd/4:21]
BUG: soft lockup - CPU#1 stuck for 67s! [events/1:36]
BUG: soft lockup - CPU#3 stuck for 62s! [rsyslogd:1325]
BUG: soft lockup - CPU#4 stuck for 72s! [events/4:39]
BUG: soft lockup - CPU#1 stuck for 70s! [automount:4252]
BUG: soft lockup - CPU#2 stuck for 73s! [hald:1685]
BUG: soft lockup - CPU#0 stuck for 61s! [automount:1776]
BUG: soft lockup - CPU#6 stuck for 67s! [events/6:41]
BUG: soft lockup - CPU#5 stuck for 67s! [vmmemctl:894]
BUG: soft lockup - CPU#7 stuck for 65s! [lldpad:1459]
BUG: soft lockup - CPU#3 stuck for 68s! [swapper:0]
BUG: soft lockup - CPU#2 stuck for 68s! [events/2:37]
BUG: soft lockup - CPU#0 stuck for 67s! [crond:1815]
BUG: soft lockup - CPU#7 stuck for 67s! [watchdog/7:34]
BUG: soft lockup - CPU#1 stuck for 68s! [events/1:36]
BUG: soft lockup - CPU#4 stuck for 67s! [watchdog/4:22]
BUG: soft lockup - CPU#5 stuck for 68s! [watchdog/5:26]
BUG: soft lockup - CPU#3 stuck for 66s! [swapper:0]
BUG: soft lockup - CPU#2 stuck for 66s! [ksoftirqd/2:13]
BUG: soft lockup - CPU#0 stuck for 67s! [watchdog/0:6]
BUG: soft lockup - CPU#5 stuck for 67s! [watchdog/5:26]
BUG: soft lockup - CPU#6 stuck for 62s! [fcoemon:1509]
BUG: soft lockup - CPU#4 stuck for 70s! [lldpad:1459]
BUG: soft lockup - CPU#7 stuck for 63s! [watchdog/7:34]
BUG: soft lockup - CPU#1 stuck for 63s! [sync_supers:48]
BUG: soft lockup - CPU#3 stuck for 63s! [irqbalance:1351]
BUG: soft lockup - CPU#2 stuck for 62s! [events/2:37]
BUG: soft lockup - CPU#0 stuck for 68s! [events/0:35]
BUG: soft lockup - CPU#2 stuck for 68s! [sa1:4687]
BUG: soft lockup - CPU#3 stuck for 78s! [flush-8:0:4618]
BUG: soft lockup - CPU#1 stuck for 78s! [events/1:36]
BUG: soft lockup - CPU#4 stuck for 63s! [lldpad:1459]
BUG: soft lockup - CPU#6 stuck for 64s! [fcoemon:1509]
BUG: soft lockup - CPU#5 stuck for 64s! [NetworkManager:1531]
BUG: soft lockup - CPU#0 stuck for 62s! [watchdog/0:6]
BUG: soft lockup - CPU#7 stuck for 68s! [watchdog/7:34]
BUG: soft lockup - CPU#4 stuck for 63s! [lldpad:1459]
BUG: soft lockup - CPU#1 stuck for 162s! [irqbalance:1351]
BUG: soft lockup - CPU#6 stuck for 128s! [hald:1685]
BUG: soft lockup - CPU#2 stuck for 130s! [sshd:4688]
BUG: soft lockup - CPU#5 stuck for 147s! [rsyslogd:1325]
BUG: soft lockup - CPU#3 stuck for 71s! [flush-8:0:4618]
BUG: soft lockup - CPU#6 stuck for 68s! [events/6:41]
BUG: soft lockup - CPU#2 stuck for 68s! [irqbalance:1351]
BUG: soft lockup - CPU#1 stuck for 68s! [su:4783]
BUG: soft lockup - CPU#7 stuck for 67s! [crond:1815]
BUG: soft lockup - CPU#5 stuck for 67s! [events/5:40]
BUG: soft lockup - CPU#0 stuck for 66s! [lldpad:1459]
BUG: soft lockup - CPU#4 stuck for 65s! [automount:4785]
　　全部都是这种错误：BUG: soft lockup - CPU#x  stuck for xs
　　这个错误是什么鬼？
　　查了一下百度，发现这是一个软死锁
　　
内核软死锁（soft lockup）bug
　　Soft lockup名称解释：所谓，soft lockup就是说，这个bug没有让系统彻底死机，但是若干个进程（或者kernel thread）被锁死在了某个状态（一般在内核区域），很多情况下这个是由于内核锁的使用的问题。
　　Linux内核对于每一个cpu都有一个监控进程，在技术界这个叫做watchdog（看门狗）。通过ps -eo ppid,pid,user,args |grep watchdog能够看见，进程名称大概是watchdog/X（数字：cpu逻辑编号1/2/3/4之类的）。这个进程或者线程每一秒钟运行一次，否则会睡眠和待机。这个进程运行会收集每一个cpu运行时使用数据的时间并且存放到属于每个cpu自己的内核数据结构。在内核中有很多特定的中断函数。这些中断函数会调用soft lockup计数，他会使用当前的时间戳与特定（对应的）cpu的内核数据结构中保存的时间对比，如果发现当前的时间戳比对应cpu保存的时间大于设定的阀值，他就假设监测进程或看门狗线程在一个相当可观的时间还没有执。Cpu软锁为什么会产生，是怎么产生的？如果linux内核是经过精心设计安排的CPU调度访问，那么怎么会产生cpu软死锁？那么只能说由于用户开发的或者第三方软件引入，看我们服务器内核panic的原因就是qmgr进程引起。因为每一个无限的循环都会一直有一个cpu的执行流程（qmgr进程示一个后台邮件的消息队列服务进程），并且拥有一定的优先级。Cpu调度器调度一个驱动程序来运行，如果这个驱动程序有问题并且没有被检测到，那么这个驱动程序将会暂用cpu的很长时间。根据前面的描述，看门狗进程会抓住（catch）这一点并且抛出一个软死锁（soft lockup）错误。软死锁会挂起cpu使你的系统不可用。
　　如果是用户空间的进程或线程引起的问题backtrace是不会有内容的，如果内核线程那么在soft lockup消息中会显示出backtrace信息。
　　简单来说： 由于系统的某个驱动程序有问题导致watchdog无法收集每一个逻辑cpu运行时使用数据并抛出一个软死锁（soft lockup）错误
　　线上服务器有8个逻辑cpu所以有8只狗
　　cat /proc/cpuinfo |grep processor
processor: 0
processor: 1
processor: 2
processor: 3
processor: 4
processor: 5
processor: 6
processor: 7
　　ps -eo ppid,pid,user,args |grep watchdog
2 6 root      [watchdog/0]
2 10 root [watchdog/1]
2 14 root [watchdog/2]
2 18 root [watchdog/3]
2 22 root [watchdog/4]
2 26 root [watchdog/5]
2 30 root [watchdog/6]
2 34 root [watchdog/7]
4852 4883 root grep watchdog

　　在/var/log/messages里找到关键信息，由于用的是vmware esxi平台，估计vmware esxi的某个硬件驱动有问题，正准备联系vmware那边的工程师解决
　　less /var/log/messages
Mar 28 18:34:55 xxx kernel: UNSUPPORTED HARDWARE DEVICE: CPU family 6 model > 59
Mar 28 18:34:55 xxx kernel: ------------[ cut here ]------------
Mar 28 18:34:55 xxx kernel: WARNING: at kernel/rh_taint.c:13 mark_hardware_unsupported+0x39/0x40() (Not tainted)
Mar 28 18:34:55 xxx kernel: Hardware name: VMware Virtual Platform
Mar 28 18:34:55 xxx kernel: Your hardware is unsupported.  Please do not report bugs, panics, oopses, etc., on this hardware.
Mar 28 18:34:55 xxx kernel: Modules linked in:
Mar 28 18:34:55 xxx kernel: Pid: 0, comm: swapper Not tainted 2.6.32-279.el6.x86_64 #1
Mar 28 18:34:55 xxx kernel: Call Trace:
Mar 28 18:34:55 xxx kernel: [<ffffffff8106b747>] ? warn_slowpath_common+0x87/0xc0
Mar 28 18:34:55 xxx kernel: [<ffffffff8106b7df>] ? warn_slowpath_fmt_taint+0x3f/0x50
Mar 28 18:34:55 xxx kernel: [<ffffffff8109a869>] ? mark_hardware_unsupported+0x39/0x40
Mar 28 18:34:55 xxx kernel: [<ffffffff81c27b5d>] ? setup_arch+0xb1f/0xb42
Mar 28 18:34:55 xxx kernel: [<ffffffff814fd223>] ? printk+0x41/0x46
Mar 28 18:34:55 xxx kernel: [<ffffffff81c21c33>] ? start_kernel+0xdc/0x430
Mar 28 18:34:55 xxx kernel: [<ffffffff81c2133a>] ? x86_64_start_reservations+0x125/0x129
Mar 28 18:34:55 xxx kernel: [<ffffffff81c21438>] ? x86_64_start_kernel+0xfa/0x109
Mar 28 18:34:55 xxx kernel: ---[ end trace a7919e7f17c0a725 ]---
Mar 28 18:34:55 xxx kernel: NR_CPUS:4096 nr_cpumask_bits:8 nr_cpu_ids:8 nr_node_ids:1
Mar 28 18:34:55 xxx kernel: PERCPU: Embedded 31 pages/cpu @ffff880028200000 s94424 r8192 d24360 u262144
Mar 28 18:34:55 xxx kernel: pcpu-alloc: s94424 r8192 d24360 u262144 alloc=1*2097152
Mar 28 18:34:55 xxx kernel: pcpu-alloc: [0] 0 1 2 3 4 5 6 7
Mar 28 18:34:55 xxx kernel: Built 1 zonelists in Zone order, mobility grouping on.  Total pages: 2064657
Mar 28 18:34:55 xxx kernel: Policy zone: Normal
Mar 28 18:34:55 xxx kernel: Kernel command line: ro root=UUID=12b1eb92-e0a3-441c-98e0-6d75d9e510c2 rd_NO_LUKS rd_NO_LVM LANG=en_US.UTF-8 rd_NO_MD SYSFONT=latarcyrheb-sun16 crashkernel=128M  KEYBOAR
DTYPE=pc KEYTABLE=us rd_NO_DM rhgb quiet
　　参考文章
http://blog.jobbole.com/110581/
http://www.cnblogs.com/brucewoo/archive/2012/12/16/3226861.html
　　如有不对的地方，欢迎大家拍砖o(&cap;_&cap;)o
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