Executing the CodeQL GitHub Action within a Docker container results in the detection of only a single CPU, due to the `/sys/fs/cgroup/cpuset.cpus` file being empty.

[thomas-koppera-keenfinity]

Hi,

when using the github action in a container action with a docker image which has cgroup v2 it cannot be run multithreaded.

Example output:

While resolving threads, found a cgroup CPUs file with 32 CPUs in /sys/fs/cgroup/cpuset.cpus.effective.
While resolving threads, found a cgroup CPUs file with 1 CPUs in /sys/fs/cgroup/cpuset.cpus.

This happens because at my docker image (ubuntu:22.04) the /sys/fs/cgroup/cpuset.cpus is empty which is legit:
see https://www.kernel.org/doc/Documentation/admin-guide/cgroup-v2.rst

If "cpuset.cpus" is empty, the "cpuset.cpus.effective" file shows
all the CPUs from the parent cgroup that can be available to
be used by this cgroup.

Now this lead to a maximum number of 1 CPU.
Relates to #2083

[angelapwen]

Hello! Thank you for reporting. I can look into this for you as I authored #2083. I'd like to understand why /sys/fs/cgroup/cpuset.cpus is reporting 1 CPU here:

codeql-action/src/util.ts

Line 469 in dc983b3

`While resolving threads, found a cgroup CPUs file with ${cpuCount} CPUs in ${cpusFile}.`,

. If I understand correctly, the file exists in your container but is empty. Is that right?

[thomas-koppera-keenfinity]

Yes the file exists, but it is empty, I'm using ubuntu 22.04 docker image.
Edit:
Empty is not correct, it has no content. It has a newline character:

$ xxd /sys/fs/cgroup/cpuset.cpus
$ 00000000: 0a

[angelapwen]

Ah, I understand why the count is reporting as 1 now. I've put up #2151 which should address this issue. Thank you!