背景：这个是之前遇到的老问题。

# systemctl status lxcfs
● lxcfs.service - FUSE filesystem for LXC
Loaded: loaded (/usr/lib/systemd/system/lxcfs.service; enabled; vendor preset: disabled)
Active: activating (start-post) since Tue 2020-06-23 14:37:50 CST; 5min ago---这个是6月份的案例，其实4月份就出过一次，不过由于运维同学急于重启，我没看到现场。
Docs: man:lxcfs(1)
Process: 415455 ExecStopPost=/bin/sh -c if mount |grep "baymax\/lxcfs"; then fusermount -u /var/lib/baymax/lxcfs; fi (code=exited, status=0/SUCCESS)
Main PID: 415526 (lxcfs); : 415529 (lxcfs-remount-c)
Tasks: 43
Memory: 28.9M
CGroup: /system.slice/lxcfs.service
├─415526 /usr/bin/lxcfs -o nonempty /var/lib/baymax/lxcfs/
└─control
├─415529 /bin/sh /usr/bin/lxcfs-remount-containers
├─416923 /bin/sh /usr/bin/lxcfs-remount-containers
└─419090 docker exec 1eb2f723b69e sh -c \ export f=/proc/cpuinfo && test -f /var/lib/baymax/lxcfs/$f && (umount $f; mount --bind…

然后看下对应的runc：

# ps -ef |grep -i runc |grep -v shim
root 172169 138974 0 14:43 pts/2 00:00:00 grep --color -i runc
root 420924 70170 0 14:37 ? 00:00:00 runc --root /var/run/docker/runtime-runc/moby --log /run/docker/containerd/daemon/io.containerd.runtime.v1.linux/moby/1eb2f723b69e2dba83bc490d3fab66922a13a4787be8bcb4cd486e97843ffef5/log.json --log-format json exec --process /tmp/runc-process904568476 --detach --pid-file /run/docker/containerd/daemon/io.containerd.runtime.v1.linux/moby/1eb2f723b69e2dba83bc490d3fab66922a13a4787be8bcb4cd486e97843ffef5/4dfeee72cd794ebec396fb8450f8944499cdde99d22054c950e5a80fb56f0968.pid 1eb2f723b69e2dba83bc490d3fab66922a13a4787be8bcb4cd486e97843ffef5
root 423656 420924 0 14:37 ? 00:00:00 runc init

然后看对应 423656  的堆栈详细信息：

PID: 423656 TASK: ffffa0e872d56180 CPU: 28 COMMAND: "runc:[2:INIT]"
#0 [ffffa13093eb3c78] __schedule at ffffffffb6969a72
ffffa13093eb3c80: 0000000000000086 ffffa13093eb3fd8
ffffa13093eb3c90: ffffa13093eb3fd8 ffffa13093eb3fd8
ffffa13093eb3ca0: 000000000001ab80 ffffa0d4f6a12080
ffffa13093eb3cb0: 0000000000000046 0000000000000000
ffffa13093eb3cc0: ffffa13093eb3d38 00000000e3a7c164
ffffa13093eb3cd0: 0000000000000246 ffffa1032ad42000
ffffa13093eb3ce0: ffffa1032ad42028 0000000000000000
ffffa13093eb3cf0: 0000000000000001 0000000000000000
ffffa13093eb3d00: ffffa13093eb3d10 ffffffffb6969f19
#1 [ffffa13093eb3d08] schedule at ffffffffb6969f19
ffffa13093eb3d10: ffffa13093eb3d60 ffffffffb644bd50
#2 [ffffa13093eb3d18] pipe_wait at ffffffffb644bd50
ffffa13093eb3d20: 0000000000000000 ffffa0e872d56180
ffffa13093eb3d30: ffffffffb62c3f50 ffffa0f072d87108
ffffa13093eb3d40: ffffa1032ad42030 00000000e3a7c164
ffffa13093eb3d50: ffffa1032ad42000 0000000000000010 -----分析堆栈，pipe的inode压栈在此
ffffa13093eb3d60: ffffa13093eb3de8 ffffffffb644bff9
#3 [ffffa13093eb3d68] pipe_write at ffffffffb644bff9
ffffa13093eb3d70: ffffa1032ad42028 ffffa0e872d56180
ffffa13093eb3d80: ffffa13093eb3df8 0000000000000000
ffffa13093eb3d90: ffffa10224b2c000 ffffffff00000000
ffffa13093eb3da0: ffffa12f3d7df300 00000ff1d12d8867
ffffa13093eb3db0: 0000000000000000 00000000e3a7c164
ffffa13093eb3dc0: ffffa13093eb3f18 000000c000008bf0
ffffa13093eb3dd0: ffffa13093eb3f18 0000000000000010
ffffa13093eb3de0: 0000000000000000 ffffa13093eb3ec0
ffffa13093eb3df0: ffffffffb6441c13
#4 [ffffa13093eb3df0] do_sync_write at ffffffffb6441c13
ffffa13093eb3df8: 000000c000008bf0 0000000000000010
ffffa13093eb3e08: 0000000000000001 ffffa12f3d7df300
ffffa13093eb3e18: 0000000000000000 0000000000000000
ffffa13093eb3e28: 0000000000000000 ffffa0e872d56180
ffffa13093eb3e38: 0000000000000000 0000000000000000
ffffa13093eb3e48: 0000000000000000 0000000000000000
ffffa13093eb3e58: 0000000000000010 0000000000000000
ffffa13093eb3e68: 0000000000000010 0000000000000000
ffffa13093eb3e78: 0000000000000000 0000000000000000
ffffa13093eb3e88: 0000000000000000 0000000000000000
ffffa13093eb3e98: 0000000000000000 0000000000000000
ffffa13093eb3ea8: 0000000000000000 00000000e3a7c164
ffffa13093eb3eb8: ffffa12f3d7df300 ffffa13093eb3f00
ffffa13093eb3ec8: ffffffffb6442700
#5 [ffffa13093eb3ec8] vfs_write at ffffffffb6442700
ffffa13093eb3ed0: 0000000000000000 ffffa12f3d7df300
ffffa13093eb3ee0: 0000000000000000 000000c000008bf0
ffffa13093eb3ef0: 0000000000000010 0000000000000000
ffffa13093eb3f00: ffffa13093eb3f48 ffffffffb644351f
#6 [ffffa13093eb3f08] sys_write at ffffffffb644351f
ffffa13093eb3f10: ffffa13093eb3f48 0000000000000000
ffffa13093eb3f20: 00000000e3a7c164 0000000000000000
ffffa13093eb3f30: 0000000000000000 0000000000000000
ffffa13093eb3f40: 0000000000000000 0000000000000000
ffffa13093eb3f50: ffffffffb6976ddb
#7 [ffffa13093eb3f50] system_call_fastpath at ffffffffb6976ddb
RIP: 000000000045b8a5 RSP: 000000c000008be8 RFLAGS: 00010206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 000000c000000000
RDX: 0000000000000010 RSI: 000000c000008bf0 RDI: 0000000000000002
RBP: 000000c000008b90 R8: 0000000000000001 R9: 00000000006c0fab
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
R13: 0000000000000000 R14: 000000000086d0d8 R15: 0000000000000000
ORIG_RAX: 0000000000000001 CS: 0033 SS: 002b

看情况是卡在pipe的write，然后看下它打开的文件，找到对应的inode信息：

PID: 423656 TASK: ffffa0e872d56180 CPU: 28 COMMAND: "runc:[2:INIT]"
ROOT: /rootfs CWD: /rootfs
FD FILE DENTRY INODE TYPE PATH
0 ffffa0feca33cf00 ffffa1333b800240 ffffa1333f568850 CHR /dev/null
1 ffffa1031adba700 ffffa0f10efb83c0 ffffa0d78de55c80 FIFO
2 ffffa12f3d7df300 ffffa0f10efb8a80 ffffa0d78de56f00 FIFO -----对应那个pipe
3 ffffa133026b9700 ffffa11382e2f080 ffffa12a2b07ad30 SOCK UNIX

验证下这个pipe：

crash> struct file.private_data ffffa12f3d7df300
private_data = 0xffffa1032ad42000
crash> pipe_inode_info 0xffffa1032ad42000--------和上面的堆栈对的上
struct pipe_inode_info {
mutex = {
count = {
counter = 1
},
wait_lock = {
{
rlock = {
raw_lock = {
val = {
counter = 0
}
}
}
}
},
wait_list = {
next = 0xffffa1032ad42008,
prev = 0xffffa1032ad42008
},
owner = 0x0,
{
osq = {
tail = {
counter = 0
}
},
__UNIQUE_ID_rh_kabi_hide3 = {
spin_mlock = 0x0
},
{}
}
},
wait = {
lock = {
{
rlock = {
raw_lock = {
val = {
counter = 0
}
}
}
}
},
task_list = {
next = 0xffffa13093eb3d38,
prev = 0xffffa0f072d87108
}
},
nrbufs = 1, ----只有一个buf，说明pipe创建的时候，page不够，这个主要受限于 pipe-user-pages-soft的默认配置，
curbuf = 0,
buffers = 1,
readers = 1,
writers = 1,
files = 2,
waiting_writers = 1,
r_counter = 1,
w_counter = 1,
tmp_page = 0x0,
fasync_readers = 0x0,
fasync_writers = 0x0,
bufs = 0xffffa132c3a3d100,
user = 0xffffffffb6e4d700
}

看下pipe中的内容：

crash> pipe_buffer 0xffffa132c3a3d100
struct pipe_buffer {
page = 0xffffe392f992cb00,
offset = 0,
len = 4081, ---内容的长度
ops = 0xffffffffb6a2e000,
flags = 0,
private = 0
}

crash> kmem -p |grep ffffe392f992cb00
ffffe392f992cb00 2e64b2c000 0 0 1 2fffff00000000

crash> rd -a -p 2e64b2c000 4081-----------这个4081就是上面的长度 2e64b2c000: runtime/cgo: pthread_create failed: Resource temporarily una 2e64b2c03c: vailable 2e64b2c045: SIGABRT: abort-----------------这个看公众号说是内存不足导致，还贴了一段其他的oom来凑数，其实是因为线程数限制导致
2e64b2c054: PC=0x6c0fab m=0 sigcode=18446744073709551610
2e64b2c082: goroutine 0 [idle]:
2e64b2c096: runtime: unknown pc 0x6c0fab
2e64b2c0b3: stack: frame={sp:0x7ffc54fb5b18, fp:0x0} stack=[0x7ffc547b6f
2e64b2c0ef: a8,0x7ffc54fb5fd0)
2e64b2c102: 00007ffc54fb5a18: 0000000000004000 0000000000000000
2e64b2c139: 00007ffc54fb5a28: 0000000000d0eb80 00007fe3c913f000
2e64b2c170: 00007ffc54fb5a38: 00007ffc54fb5a58 00007ffc54fb5a88
2e64b2c1a7: 00007ffc54fb5a48: 000000000040eb32 00007ffc54fb5a60
2e64b2c1fc: 00007ffc54fb5a58: 00007ffc54fb5aa0 00007ffc54fb5ab0
2e64b2c233: 00007ffc54fb5a68: 0000000000000040 0000000000000040
2e64b2c26a: 00007ffc54fb5a78: 0000000000000001 0000000000000002
2e64b2c2a1: 00007ffc54fb5a88: 00000000006b7ebc 000000000041a229
2e64b2c2f8: 00007ffc54fb5a98: 000000000045bdde
2e64b2c334: 00007ffc54fb5aa0
2e64b2c348: 00007ffc54fb5aa8: 0000000000d0eb80 0000000054fb5af0
2e64b2c37f: 00007ffc54fb5ab8: 0000000000454d48
2e64b2c3bb: 000000000041a19b
2e64b2c3ee: 00007ffc54fb5ac8: 00007fe3c913f000 0000000000000030
2e64b2c425: 00007ffc54fb5ad8: 0000000000000030 0000000000000030
2e64b2c45c: 00007ffc54fb5ae8: 0000000000cd4c28 00000000008814b6
2e64b2c493: 00007ffc54fb5af8: 0000000001cd3db0 0000000000000011
2e64b2c4ca: 00007ffc54fb5b08: 000000000086d0d8 0000000000000000
2e64b2c501: 00007ffc54fb5b18: <00000000006d6198 0000000000000020 2e64b2c538: 00007ffc54fb5b28: 0000000000000000 0000000000000000 2e64b2c56f: 00007ffc54fb5b38: 0000000000000000 0000000000000000 2e64b2c5a6: 00007ffc54fb5b48: 0000000000000000 0000000000000000 2e64b2c5dd: 00007ffc54fb5b58: 0000000000000000 0000000000000000 2e64b2c614: 00007ffc54fb5b68: 0000000000000000 0000000000000000 2e64b2c64b: 00007ffc54fb5b78: 0000000000000000 0000000000000000 2e64b2c682: 00007ffc54fb5b88: 0000000000000000 0000000000000000 2e64b2c6b9: 00007ffc54fb5b98: 0000000000000000 000000000000000d 2e64b2c6f0: 00007ffc54fb5ba8: 00000000006c01bd 0000000000000000 2e64b2c727: 00007ffc54fb5bb8: 00000000006e97e3 00007fe3c913b558 2e64b2c75e: 00007ffc54fb5bc8: 0000000000cd4580 0000000000000001 2e64b2c795: 00007ffc54fb5bd8: 0000000000cd4603 0000000000a9d760 2e64b2c7cc: 00007ffc54fb5be8: 00000000006ea87b 0000000000cd4580 2e64b2c803: 00007ffc54fb5bf8: 000000000000000a 0000000001cd3db0 2e64b2c83a: 00007ffc54fb5c08: 0000000000000011 000000000086d0d8 2e64b2c871: runtime: unknown pc 0x6c0fab 2e64b2c88e: stack: frame={sp:0x7ffc54fb5b18, fp:0x0} stack=\[0x7ffc547b6f 2e64b2c8ca: a8,0x7ffc54fb5fd0) 2e64b2c8dd: 00007ffc54fb5a18: 0000000000004000 0000000000000000 2e64b2c914: 00007ffc54fb5a28: 0000000000d0eb80 00007fe3c913f000 2e64b2c94b: 00007ffc54fb5a38: 00007ffc54fb5a58 00007ffc54fb5a88 2e64b2c982: 00007ffc54fb5a48: 000000000040eb32 00007ffc54fb5a60
2e64b2c9d7: 00007ffc54fb5a58: 00007ffc54fb5aa0 00007ffc54fb5ab0
2e64b2ca0e: 00007ffc54fb5a68: 0000000000000040 0000000000000040
2e64b2ca45: 00007ffc54fb5a78: 0000000000000001 0000000000000002
2e64b2ca7c: 00007ffc54fb5a88: 00000000006b7ebc 000000000041a229
2e64b2cad3: 00007ffc54fb5a98: 000000000045bdde
2e64b2cb0f: 00007ffc54fb5aa0
2e64b2cb23: 00007ffc54fb5aa8: 0000000000d0eb80 0000000054fb5af0
2e64b2cb5a: 00007ffc54fb5ab8: 0000000000454d48
2e64b2cb96: 000000000041a19b
2e64b2cbc9: 00007ffc54fb5ac8: 00007fe3c913f000 0000000000000030
2e64b2cc00: 00007ffc54fb5ad8: 0000000000000030 0000000000000030
2e64b2cc37: 00007ffc54fb5ae8: 0000000000cd4c28 00000000008814b6
2e64b2cc6e: 00007ffc54fb5af8: 0000000001cd3db0 0000000000000011
2e64b2cca5: 00007ffc54fb5b08: 000000000086d0d8 0000000000000000
2e64b2ccdc: 00007ffc54fb5b18: <00000000006d6198 0000000000000020
2e64b2cd13: 00007ffc54fb5b28: 0000000000000000 0000000000000000
2e64b2cd4a: 00007ffc54fb5b38: 0000000000000000 0000000000000000
2e64b2cd81: 00007ffc54fb5b48: 0000000000000000 0000000000000000
2e64b2cdb8: 00007ffc54fb5b58: 0000000000000000 0000000000000000
2e64b2cdef: 00007ffc54fb5b68: 0000000000000000 0000000000000000
2e64b2ce26: 00007ffc54fb5b78: 0000000000000000 0000000000000000
2e64b2ce5d: 00007ffc54fb5b88: 0000000000000000 0000000000000000
2e64b2ce94: 00007ffc54fb5b98: 0000000000000000 000000000000000d
2e64b2cecb: 00007ffc54fb5ba8: 00000000006c01bd 0000000000000000
2e64b2cf02: 00007ffc54fb5bb8: 00000000006e97e3 00007fe3c913b558
2e64b2cf39: 00007ffc54fb5bc8: 0000000000cd4580 0000000000000001
2e64b2cf70: 00007ffc54fb5bd8: 0000000000cd4603 0000000000a9d760
2e64b2cfa7: 00007ffc54fb5be8: 00000000006ea87b 0000000000cd4580
2e64b2cfde: 00007ffc54fb5bf8:

然后看下对端为啥没有来读：

crash> pipe_inode_info.wait 0xffffa1032ad42000
wait = {
lock = {
{
rlock = {
raw_lock = {
val = {
counter = 0
}
}
}
}
},
task_list = {
next = 0xffffa13093eb3d38, --------__wait_queue的task_list链串在此
prev = 0xffffa0f072d87108
}
}
crash> __wait_queue 0xffffa13093eb3d20
struct __wait_queue {
flags = 0,
private = 0xffffa0e872d56180, ----对应的就是 423656
func = 0xffffffffb62c3f50,
task_list = {
next = 0xffffa0f072d87108,
prev = 0xffffa1032ad42030
}
}

根据fd的对端信息，可以找到其父进程，也就是shim进程是等待runc退出再去读取pipe，而runc又因为pipe容量不够而不退出，所以形成了死锁。

我们的解决方案是：

1.增加 pipe-user-pages-soft 的配置。

2.监控user_struct.pipe_bufs 的用量。

3.建议不要去动shim 中等待runc退出在读取pipe的逻辑，除非大的故障，谁吃饱了没事去升级一遍containerd-shim。

4.runc存活时间监控。

ps：docker hung住的问题案例很多，比如删除容器的时候遇到容器内的进程D状态等等。