Panic while trying to inspect cgroup

[clebio]

I'm following your walkthrough.md, using a Vagrant box, and got a panic.

Looking at the namespace,

vagrant@ubuntu-14:~$ sudo cinf --namespace 4026532177

 PID    PPID   NAME   CMD                   NTHREADS  CGROUPS                                                                                  STATE

 12397  12379  nginx  nginx: master proces  1         11:hugetlb:/docker/9d46982572191c4b7f8a11598102068ce6d8fed1b09d53b742f4e0598ce614f1      S (sleeping)
                                                      10:perf_event:/docker/9d46982572191c4b7f8a11598102068ce6d8fed1b09d53b742f4e0598ce614f1
                                                      9:blkio:/docker/9d46982572191c4b7f8a11598102068ce6d8fed1b09d53b742f4e0598ce614f1
                                                      8:freezer:/docker/9d46982572191c4b7f8a11598102068ce6d8fed1b09d53b742f4e0598ce614f1
                                                      7:devices:/docker/9d46982572191c4b7f8a11598102068ce6d8fed1b09d53b742f4e0598ce614f1
                                                      6:memory:/docker/9d46982572191c4b7f8a11598102068ce6d8fed1b09d53b742f4e0598ce614f1
                                                      5:cpuacct:/docker/9d46982572191c4b7f8a11598102068ce6d8fed1b09d53b742f4e0598ce614f1
                                                      4:cpu:/docker/9d46982572191c4b7f8a11598102068ce6d8fed1b09d53b742f4e0598ce614f1
                                                      3:cpuset:/docker/9d46982572191c4b7f8a11598102068ce6d8fed1b09d53b742f4e0598ce614f1
                                                      2:name=systemd:/docker/9d46982572191c4b7f8a11598102068ce6d8fed1b09d53b742f4e0598ce614f1
 12434  12397  nginx  nginx: worker proces  1         11:hugetlb:/docker/9d46982572191c4b7f8a11598102068ce6d8fed1b09d53b742f4e0598ce614f1      S (sleeping)
                                                      10:perf_event:/docker/9d46982572191c4b7f8a11598102068ce6d8fed1b09d53b742f4e0598ce614f1
                                                      9:blkio:/docker/9d46982572191c4b7f8a11598102068ce6d8fed1b09d53b742f4e0598ce614f1
                                                      8:freezer:/docker/9d46982572191c4b7f8a11598102068ce6d8fed1b09d53b742f4e0598ce614f1
                                                      7:devices:/docker/9d46982572191c4b7f8a11598102068ce6d8fed1b09d53b742f4e0598ce614f1
                                                      6:memory:/docker/9d46982572191c4b7f8a11598102068ce6d8fed1b09d53b742f4e0598ce614f1
                                                      5:cpuacct:/docker/9d46982572191c4b7f8a11598102068ce6d8fed1b09d53b742f4e0598ce614f1
                                                      4:cpu:/docker/9d46982572191c4b7f8a11598102068ce6d8fed1b09d53b742f4e0598ce614f1
                                                      3:cpuset:/docker/9d46982572191c4b7f8a11598102068ce6d8fed1b09d53b742f4e0598ce614f1
                                                      2:name=systemd:/docker/9d46982572191c4b7f8a11598102068ce6d8fed1b09d53b742f4e0598ce614f1

Then by process ID,

vagrant@ubuntu-14:~$ sudo cinf --cgroup 12397:4

 CONTROLFILE            VALUE

 cpu.cfs_quota_us       -1
 cpu.shares             256
 cpu.stat               nr_periods 0 nr_throttled 0
                        throttled_time 0
 notify_on_release      0
 tasks                  12397 12434
 cgroup.clone_children  0
 cgroup.procs           12397 12434
 cpu.cfs_period_us      100000

And that's all as-expected. However, I didn't realize at first that I needed to supply the PID not the namespace ID, and so instead tried:

vagrant@ubuntu-14:~$ sudo cinf --cgroup 4026532177:4
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x0 pc=0x472261]

goroutine 1 [running]:
panic(0x54f520, 0xc8200160d0)
        /usr/local/go/src/runtime/panic.go:481 +0x3e6
github.com/mhausenblas/cinf/namespaces.usage(0x7fff7662e97f, 0xa, 0x7fff7662e98a, 0x1, 0x2, 0x0, 0x0)
        /Users/mhausenblas/Dropbox/dev/work/src/github.com/mhausenblas/cinf/namespaces/namespaces.go:198 +0xb11
github.com/mhausenblas/cinf/namespaces.LookupCG(0x7fff7662e97f, 0xc)
        /Users/mhausenblas/Dropbox/dev/work/src/github.com/mhausenblas/cinf/namespaces/namespaces.go:275 +0x331
main.main()
        /Users/mhausenblas/Dropbox/dev/work/src/github.com/mhausenblas/cinf/main.go:85 +0xdf

I realize this isn't a valid cgroup identifier, 4026532177:4, however, cinf shouldn't outright crash, eh?

For context, I'm using:

vagrant@ubuntu-14:~$ cat /etc/os-release
NAME="Ubuntu"
VERSION="14.04, Trusty Tahr"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 14.04 LTS"
VERSION_ID="14.04"
HOME_URL="http://www.ubuntu.com/"
SUPPORT_URL="http://help.ubuntu.com/"
BUG_REPORT_URL="http://bugs.launchpad.net/ubuntu/"

vagrant@ubuntu-14:~$ docker --version
Docker version 18.06.1-ce, build e68fc7a

vagrant@ubuntu-14:~$ cinf --version
     ___                    ___          ___
    /\__\                  /\  \        /\__\
   /:/  /       ___        \:\  \      /:/ _/_
  /:/  /       /\__\        \:\  \    /:/ /\__\
 /:/  /  ___  /:/__/    _____\:\  \  /:/ /:/  /
/:/__/  /\__\/::\  \   /::::::::\__\/:/_/:/  /
\:\  \ /:/  /\/\:\  \__\:\~~\~~\/__/\:\/:/  /
 \:\  /:/  /  ~~\:\/\__\\:\  \       \::/__/
  \:\/:/  /      \::/  / \:\  \       \:\  \
   \::/  /       /:/  /   \:\__\       \:\__\
    \/__/        \/__/     \/__/        \/__/

This is cinf in version 0.4.0
See also https://github.com/mhausenblas/cinf

Thanks for this awesome tool and small Go utility! It is encouraging me to dig deeper into my understanding of containers.
(updated to fix markdown escaping)

[clebio]

Hmm, I guess it's just printing the error. Ok.
https://github.com/mhausenblas/cinf/blob/master/namespaces/namespaces.go#L293

[mhausenblas]

Thanks @clebio and will have a look ASAP.