defunct processes, the possible explanation

[sterchelen]

introduction

The following explanation is focused on using csi-s3 with goofys as a backend. All the components are in their latest version. The issue I stumbled upon is the number of goofys Zombie processes. The number doesn't have any importance in the understanding.

explanation

I looked in the csi-s3 code and more importantly at the FuseUnmount function and then at waitForProcess https://github.com/ctrox/csi-s3/blob/ddbd6fdaa1bd76754df3ea76fba0afe149ebe87d/pkg/mounter/mounter.go#L133-L156

Due to the name of the function I was expected to see a wait4 syscall to consume the child process, in our case goofys. If we look at the below outputs:

• we have a goofys Zombie process with pid=32767

$ ps aux | grep goofys
root     32767  0.0  0.0      0     0 ?        Zs   Jun14   0:00 [goofys] <defunct>

• its parent process the s3driver

  $ pstree -s 32767
  systemd───containerd-shim───s3driver───goofys

  As s3driver launches goofys backend (I guess it is the case for the other backends 🤷🏼‍♂️), s3driver is the parent process. Then as a good parent 😃 it should wait4 its child to know what was its status.

In other words, there is a leak on child termination. The fix should be trivial; in the waitForProcess when the cmdLine is empty, we have to syscall.wait4 on the given pid. https://github.com/ctrox/csi-s3/blob/ddbd6fdaa1bd76754df3ea76fba0afe149ebe87d/pkg/mounter/mounter.go#L142-L148

wdyt @ctrox?