Re: [PATCH bpf-next 5/6] bpf: Improve tracing recursion prevention mechanism

[Yafang Shao <laoar.shao@gmail.com>]

On Thu, Apr 27, 2023 at 11:39 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Thu, Apr 27, 2023 at 8:36 AM Steven Rostedt <rostedt@goodmis.org> wrote:
> >
> > On Thu, 27 Apr 2023 23:23:31 +0800
> > Yafang Shao <laoar.shao@gmail.com> wrote:
> >
> > > > But I thought you can run a bpf_prog from another bpf_prog. So you don't
> > > > want to prevent it. You need other logic to detect if it was not suppose to
> > > > recurs.
> > > >
> > >
> > > If so, we have to keep the prog->active to prevent it, then I'm not
> > > sure if it is worth adding test_recursion_*().
> >
> > I thought that the whole point of this exercise was because the
> > migrate_disable() itself could be traced (or call something that can), and
> > that's outside of prog->active protection. Which the test_recursion_*()
> > code was created for.
>
> Not sure where did this come from.
> migrate_enable/disable were added to deny list back in 2021.

Hi Alexei,

Don't be uneasy.  It is not good to play word games.
What Steven really meant is the preempt_count_{sub, add}.
Anyway thanks Steven for the help with this exercise.

-- 
Regards
Yafang