Re: [PATCH bpf-next v6 2/2] selftests/bpf: Add testcase for bpf_task_under_cgroup

[Yonghong Song]

On 5/5/23 12:24 AM, Feng Zhou wrote:
> 在 2023/5/5 15:13, Hao Luo 写道:
> > On Thu, May 4, 2023 at 11:08 PM Feng zhou <zhoufeng.zf@xxxxxxxxxxxxx> 
> > wrote:
> > > From: Feng Zhou <zhoufeng.zf@xxxxxxxxxxxxx>
> > >
> > > test_progs:
> > > Tests new kfunc bpf_task_under_cgroup().
> > >
> > > The bpf program saves the new task's pid within a given cgroup to
> > > the remote_pid, which is convenient for the user-mode program to
> > > verify the test correctness.
> > >
> > > The user-mode program creates its own mount namespace, and mounts the
> > > cgroupsv2 hierarchy in there, call the fork syscall, then check if
> > > remote_pid and local_pid are unequal.
> > >
> > > Signed-off-by: Feng Zhou <zhoufeng.zf@xxxxxxxxxxxxx>
> > > Acked-by: Yonghong Song <yhs@xxxxxx>
> > > ---
> >
> > Hi Feng,
> >
> > I have a comment about the methodology of the test, but the patch
> > looks ok to me. Why do we have to test via a tracing program? I think
> > what we need is just a task and a cgroup. Since we have the kfunc
> > bpf_task_from_pid() and bpf_cgroup_from_id(), we can write a syscall
> > program which takes a pid and a cgroup id as input and get the task
> > and cgroup objects directly in the program.
> >
> > I like testing via a syscall program because it doesn't depend on the
> > newtask tracepoint and it should be simpler. But I'm ok with the
> > current version of the patch, just have some thoughts.
> >
> > Hao
>
> Yes, your method is also very good. The reason why I did this is because 
> of Song's suggestion before, hope that the parameter of the hook point 
> will have a task, so I chose this to test.

The motivation of this patch is:
  Trace sched related functions, such as enqueue_task_fair, it is 
necessary to
  specify a task instead of the current task which within a given cgroup.

So I think it is okay to have a test related to sched.