Re: [PATCH] perf/kprobe: maxactive for fd-based kprobe

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Sat, 11 Jun 2022 11:28:36 -0700
Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:

> On Thu, Jun 9, 2022 at 1:14 PM Dmitry Dolgov <9erthalion6@gmail.com> wrote:
> >
> > > On Thu, Jun 09, 2022 at 09:29:36PM +0200, Dmitrii Dolgov wrote:
> > >
> > > Enable specifying maxactive for fd based kretprobe. This will be useful
> > > for tracing tools like bcc and bpftrace (see for example discussion [1]).
> > > Use highest 12 bit (bit 52-63) to allow maximal maxactive of 4095.
> > >
> > > The original patch [2] seems to be fallen through the cracks and wasn't
> > > applied. I've merely rebased the work done by Song Liu and verififed it
> > > still works.
> > >
> > > [1]: https://github.com/iovisor/bpftrace/issues/835
> > > [2]: https://lore.kernel.org/all/20191007223111.1142454-1-songliubraving@fb.com/
> >
> > I've recently stumbled upon this seemingly lost topic, and wanted to raise it
> > again. Please let me know if there is a more appropriate way to do so.
> 
> With kretprobe using rethook the maxactive limit is no longer used.
> So we probably don't need this patch.
> 
> Masami, wdyt?

No, rethook is just a library version of kretprobe return hook,
so the maxactive is still alive. I would like to make the rethook
to use(share with) function graph's per-task shadow stack. When
that is done, the maxactive will be removed.

Thank you,


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>