Re: [PATCH testsuite] tests/task_setscheduler: add cgroup v2 case for moving proc to root cgroup

[Gong Ruiqi <gongruiqi1@huawei.com>]

On 2024/07/26 21:43, Ondrej Mosnacek wrote:
> On Thu, Jul 18, 2024 at 2:34 PM Gong Ruiqi <gongruiqi1@huawei.com> wrote:
>>
>>
>> On 2024/07/18 0:17, Paul Moore wrote:
>>> ...
>>>
>>> Where (what distribution, version, etc.) did you see this problem?
>>
>> The problem occurred when I ran the testsuite on Fedora 40 with v6.6
>> kernel, and it was the only failed testcase.
> 
> Sorry for the delay... For some reason the test passes for me even
> with cgroup v2 only and without the patch (also when run from a
> regular user account with sudo). Do you happen to know what
> circumstances are needed for it to fail when the cgroup is not
> switched?
> 

As the comment in the script says, a process need to be in the root
cgroup in order to switch its scheduler policy to SCHED_{RR,FIFO}. So
maybe in your case the shell process is already in the root cgroup?

In my case I need to ssh to a Fedora VM, and that makes my shell process
to be in a sub cgroup called /user.slice/.../XXX.scope (looks like some
systemd stuff). And since /sys/fs/cgroup/cpu/tasks doesn't exit in the
system with cgroup v2 only, the script skips moving the target process
to the root cgroup, and therefore the subsequent test fails.