【问题实操】银河麒麟高级服务器操作系统实例，CPU软锁报错触发宕机

1.服务器环境以及配置

处理器：	Kunpeng 920
内存：	256G DDR4
整机类型/架构：	TaiShan 200 (Model 2280)
内核版本	4.19.90-23.8.v2101.ky10.aarch64

2.问题现象描述

两台搭载麒麟v10 sp1的机器均在系统CPU软锁报错时，触发了softlockup_panic宕机。

3.问题分析

3.1.分析kylin1日志

3.1.1. 分析vmcore-dmesg日志

3.2.分析kylin2日志

3.2.1.分析messages日志

从messages日志看，系统不断出现软锁。

Dec 4 23:06:46 localhost sh[2145769]: [docker][INFO] do health check success [200]
Dec 4 23:06:47 localhost kernel: [2805817.816879] watchdog: BUG: soft lockup - CPU#17 stuck for 22s! [migration/17:96]
Dec 4 23:06:47 localhost kernel: [2805817.824909] CPU: 17 PID: 96 Comm: migration/17 Kdump: loaded Tainted: G W L 4.19.90-23.8.v2101.ky10.aarch64 #1
Dec 4 23:06:47 localhost kernel: [2805817.824910] Hardware name: Huawei TaiShan 200 (Model 2280)/BC82AMDGK, BIOS 1.77 06/28/2021
Dec 4 23:06:47 localhost kernel: [2805817.824911] pstate: 60c00009 (nZCv daif +PAN +UAO)
Dec 4 23:06:47 localhost kernel: [2805817.824916] pc : multi_cpu_stop+0xe0/0x170
Dec 4 23:06:47 localhost kernel: [2805817.824917] lr : 0x2
Dec 4 23:06:47 localhost kernel: [2805817.824918] sp : ffff803fc73f3d70
Dec 4 23:06:47 localhost kernel: [2805817.824933] Call trace:
Dec 4 23:06:47 localhost kernel: [2805817.824935] multi_cpu_stop+0xe0/0x170
Dec 4 23:06:47 localhost kernel: [2805817.824936] cpu_stopper_thread+0xd4/0x160
Dec 4 23:06:47 localhost kernel: [2805817.824938] smpboot_thread_fn+0x184/0x1b8
Dec 4 23:06:47 localhost kernel: [2805817.824941] kthread+0x134/0x138
Dec 4 23:06:47 localhost kernel: [2805817.824943] ret_from_fork+0x10/0x18
Dec 4 23:06:51 localhost kernel: [2805821.817361] watchdog: BUG: soft lockup - CPU#34 stuck for 23s! [runc:[2:INIT]:826254]
Dec 4 23:06:51 localhost kernel: [2805821.825827] CPU: 34 PID: 826254 Comm: runc:[2:INIT] Kdump: loaded Tainted: G W L 4.19.90-23.8.v2101.ky10.aarch64 #1
Dec 4 23:06:51 localhost kernel: [2805821.825828] Hardware name: Huawei TaiShan 200 (Model 2280)/BC82AMDGK, BIOS 1.77 06/28/2021
Dec 4 23:06:51 localhost kernel: [2805821.825840] pc : get_dominating_id+0x4c/0xb8
Dec 4 23:06:51 localhost kernel: [2805821.825847] lr : show_mountinfo+0x10c/0x2d8
Dec 4 23:06:51 localhost kernel: [2805821.825848] sp : ffffa03ca09bfc60
Dec 4 23:06:51 localhost kernel: [2805821.825848] x29: ffffa03ca09bfc60 x28: 00000040009652da
Dec 4 23:06:51 localhost kernel: [2805821.825850] x27: 0000000000080b26 x26: 0000000000000001
Dec 4 23:06:51 localhost kernel: [2805821.825851] x25: ffff000009114000 x24: ffffa0218a4cc808
Dec 4 23:06:51 localhost kernel: [2805821.825852] x23: ffff803783107500 x22: ffffa0218a4cc808
Dec 4 23:06:51 localhost kernel: [2805821.825853] x21: ffffa02c64372680 x20: ffff803206622400
Dec 4 23:06:51 localhost kernel: [2805821.825854] x19: ffffa03e4a6f1080 x18: 0000000000000000
Dec 4 23:06:51 localhost kernel: [2805821.825855] x17: 0000000000000000 x16: 0000000000000000
Dec 4 23:06:51 localhost kernel: [2805821.825856] x15: ffffffffffffffff x14: ffffa03f26920000
Dec 4 23:06:51 localhost kernel: [2805821.825857] x13: ffffa03f26917b88 x12: 0000000000000008
Dec 4 23:06:51 localhost kernel: [2805821.825858] x11: 0101010101010101 x10: 7f7f7f7f7f7f7f7f
Dec 4 23:06:51 localhost kernel: [2805821.825859] x9 : fefefefefefeff64 x8 : 7f7f7f7f7f7f7f7f
Dec 4 23:06:51 localhost kernel: [2805821.825860] x7 : 6c6873606b64712b x6 : ffffa03f26917c08
Dec 4 23:06:51 localhost kernel: [2805821.825861] x5 : 0000000000000000 x4 : ffffffffffffffff
Dec 4 23:06:51 localhost kernel: [2805821.825862] x3 : 0000000000000065 x2 : 0000000000000009
Dec 4 23:06:51 localhost kernel: [2805821.825863] x1 : ffffa0218a4cc808 x0 : ffff803f7ace8180
Dec 4 23:06:51 localhost kernel: [2805821.825865] Call trace:
Dec 4 23:06:51 localhost kernel: [2805821.825867] get_dominating_id+0x4c/0xb8
Dec 4 23:06:51 localhost kernel: [2805821.825868] show_mountinfo+0x10c/0x2d8
Dec 4 23:06:51 localhost kernel: [2805821.825872] m_show+0x30/0x40
Dec 4 23:06:51 localhost kernel: [2805821.825875] seq_read+0x2b4/0x4a8
Dec 4 23:06:51 localhost kernel: [2805821.825881] __vfs_read+0x48/0x80
Dec 4 23:06:51 localhost kernel: [2805821.825882] vfs_read+0x94/0x150
Dec 4 23:06:51 localhost kernel: [2805821.825884] ksys_read+0x5c/0xc8
Dec 4 23:06:51 localhost kernel: [2805821.825885] __arm64_sys_read+0x24/0x30
Dec 4 23:06:51 localhost kernel: [2805821.825890] el0_svc_common+0x78/0x130
Dec 4 23:06:51 localhost kernel: [2805821.825891] el0_svc_handler+0x38/0x78
Dec 4 23:06:51 localhost kernel: [2805821.825894] el0_svc+0x8/0x1b0
Dec 4 23:06:53 localhost systemd[1]: titanagent_check_exception.service: Succeeded.
Dec 4 23:06:53 localhost systemd[1]: Started titanagent check exception.

3.2.2.分析vmcore-dmesg日志

runc出现大量的软锁，软锁日志如下 pc : get_dominating_id+0x58/0xb8， lr : show_mountinfo+0x10c/0x2d8，从lr寄存器看，是在查看挂载信息。

[2935812.854382] watchdog: BUG: soft lockup - CPU#55 stuck for 22s! [runc:[2:INIT]:926483]
[2936044.851805] watchdog: BUG: soft lockup - CPU#32 stuck for 22s! [runc:[2:INIT]:783242]
[2936096.851768] watchdog: BUG: soft lockup - CPU#41 stuck for 23s! [runc:[2:INIT]:858586]
[2936096.852292] watchdog: BUG: soft lockup - CPU#55 stuck for 23s! [runc:[2:INIT]:926483]
[2936096.852443] watchdog: BUG: soft lockup - CPU#59 stuck for 23s! [runc:[2:INIT]:890626]
[2935608.854965] watchdog: BUG: soft lockup - CPU#30 stuck for 22s! [runc:[2:INIT]:895896]
[2935608.863423] CPU: 30 PID: 895896 Comm: runc:[2:INIT] Kdump: loaded Tainted: G W L 4.19.90-23.8.v2101.ky10.aarch64 #1
[2935608.863424] Hardware name: Huawei TaiShan 200 (Model 2280)/BC82AMDGK, BIOS 1.77 06/28/2021
[2935608.863426] pstate: 20400009 (nzCv daif +PAN -UAO)
[2935608.863431] pc : get_dominating_id+0x58/0xb8
[2935608.863434] lr : show_mountinfo+0x10c/0x2d8
[2935608.863434] sp : ffffa03f34f1fc60
[2935608.863436] x29: ffffa03f34f1fc60 x28: 0000004000f4b26a
[2935608.863437] x27: 0000000000260b96 x26: 0000000000000001
[2935608.863438] x25: ffff000009114000 x24: ffff803782bf3d08
[2935608.863439] x23: ffffa021a417a680 x22: ffff803782bf3d08
[2935608.863440] x21: ffffa02c6579bf80 x20: ffff802363223a80
[2935608.863441] x19: ffffa0218fc72880 x18: 0000000000000000
[2935608.863442] x17: 0000000000000000 x16: 0000000000000000
[2935608.863443] x15: ffffffffffffffff x14: ffffa03f73540000
[2935608.863444] x13: ffffa03f7353d768 x12: 0000000000000008
[2935608.863444] x11: 0101010101010101 x10: 7f7f7f7f7f7f7f7f
[2935608.863445] x9 : fefefefefefeff64 x8 : 7f7f7f7f7f7f7f7f
[2935608.863446] x7 : 6c6873606b64712b x6 : ffffa03f7353d7e8
[2935608.863447] x5 : 0000000000000000 x4 : ffffffffffffffff
[2935608.863448] x3 : 0000000000000065 x2 : 0000000000000009
[2935608.863449] x1 : ffff803782bf3d08 x0 : ffff803786efd480
[2935608.863451] Call trace:
[2935608.863453] get_dominating_id+0x58/0xb8
[2935608.863454] show_mountinfo+0x10c/0x2d8
[2935608.863456] m_show+0x30/0x40
[2935608.863458] seq_read+0x2b4/0x4a8
[2935608.863461] __vfs_read+0x48/0x80
[2935608.863462] vfs_read+0x94/0x150
[2935608.863463] ksys_read+0x5c/0xc8
[2935608.863464] __arm64_sys_read+0x24/0x30
[2935608.863466] el0_svc_common+0x78/0x130
[2935608.863468] el0_svc_handler+0x38/0x78
[2935608.863469] el0_svc+0x8/0x1b0

整理堆栈的函数调用，如下所示：

__arm64_sys_read+0x24/0x30
-> ksys_read+0x5c/0xc8
-> vfs_read+0x94/0x150
__vfs_read+0x48/0x80 //虚拟文件系统层（VFS）的读取操作函数
seq_read+0x2b4/0x4a8 //通常用于从顺序文件中读取数据，可能是与/proc文件系统相关的操作
m_show+0x30/0x40 //可能是一个用于将信息显示到某个输出（如控制台或日志）的函数
show_mountinfo+0x10c/0x2d8 //显然是用来展示挂载信息的，/proc/[pid]/mountinfo文件包含了进程的挂载点信息。这表明软锁可能发生在处理文件系统挂载相关的操作时。
get_dominating_id+0x54/0xb8 //可能与获取某种类型的ID（可能是进程ID、线程ID或资源ID）有关

3.2.3.分析vmcore

查看当时的内存使用情况，可见当时的空闲内存还有很多。

分析软锁堆栈的PC寄存器 get_dominating_id+0x58/0xb8，可见一直在执行/fs/pnode.c: 45

查看/fs/pnode.c: 45的源码如下，可见当时卡在do{}while循环出不来，这是因为m = next_peer(m);一直找不到尽头，最后内核一直在循环遍历。

vmcore中查看mount信息

发现有很多

/dev/mapper/klas-root 挂载到/mnt/paas/kubernetes/kubelet/plugins/kubernetes.io/csi/pv。这是不正常的。

查看各个struct mount.mnt_ns，发现都是相同的，说明struct mnt_namespace相同。

3.3. 问题复现测试

使用如下脚本复现了重复挂载

#!/bin/bash

for ((i=0; i<1000; i++))
do
# 在新的命名空间中执行挂载操作
mount --bind / /mnt/mybindmount
done

4.问题分析结果

分析两台机器的vmcore-dmesg.txt日志。软锁可能发生在runc进程尝试从某个文件（可能是与文件系统挂载相关的文件）中读取数据时。由于某种原因，这个读取操作卡住了。

分析vmcore，查看软锁时的堆栈情况，可见 pc : get_dominating_id+0x58/0xb8， lr : show_mountinfo+0x10c/0x2d8，从lr寄存器看，是在查看挂载信息出现了软锁。

查看pc寄存器所对应的内核代码，可见当时正处于一个查看mount的循环中无法出来。使用crash分析vmcore发现mount过多，有无数条/dev/mapper/klas-root 挂载到/mnt/paas/kubernetes/kubelet/plugins/kubernetes.io/csi/pv的记录，导致遍历这些记录的时候，内核进入一个死循环，最后触发软锁。

需应用端检查是否存在类似于循环挂载/dev/mapper/klas-root 挂载到/mnt/paas/kubernetes/kubelet/plugins/kubernetes.io/csi/pv的情况。例如循环执行 mount --bind / /mnt/paas/kubernetes/kubelet/plugins/kubernetes.io/csi/pv。