test_percpu failing on Fedora 36

[chantra]

As part of updating what version of Fedora BCC can be tested against, it appears that test_percpu.py is failing on Fedora 36:
https://gist.github.com/chantra/d37f3daa969bdbc07862dc11f8384a38

The underlying reason is that the test expects calls to clone, but on Fedora 36, vfork is called instead:

[root@940cbfdf11e3 /]# strace -f python3 -c 'import os; os.popen("hostname");' 2>&1 | egrep '(clone|fork)'
vfork(strace: Process 46 attached
[pid    45] <... vfork resumed>)        = 46

Python version is:

[root@940cbfdf11e3 /]# python3 -V
Python 3.10.6

os.popen uses subprocess.Popen under the hood

This is due to a change in 3.10: https://docs.python.org/3/whatsnew/changelog.html#id150

bpo-35823: Use vfork() instead of fork() for subprocess.Popen() on Linux to improve performance in cases where it is deemed safe.

Per

gh-91401: Provide a fail-safe way to disable subprocess use of vfork() via a private subprocess._USE_VFORK attribute. While there is currently no known need for this, if you find a need please only set it to False. File a CPython issue as to why you needed it and link to that from a comment in your code. This attribute is documented as a footnote in 3.11.

it can be disabled:

[root@940cbfdf11e3 /]# strace -f python3 -c 'import os; import subprocess; subprocess._USE_VFORK = False; os.popen("hostname");' 2>&1 | egrep '(clone|fork)'
clone(child_stack=NULL, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLDstrace: Process 67 attached
[root@940cbfdf11e3 /]# strace -f python3 -c 'import os; import subprocess; os.popen("hostname");' 2>&1 | egrep '(clone|fork)'
vfork(strace: Process 73 attached
[pid    72] <... vfork resumed>)        = 73

regardless, this either need to be gated based on python version, which is sub-optimal and add more conditionals to the code... or use another syscall.

I am suggesting tracing execve instead.