lkml.org 
[lkml]   [2021]   [Aug]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v4] [RFC] trace: Add kprobe on tracepoint
On Thu, 12 Aug 2021 09:44:39 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Thu, 12 Aug 2021 20:31:10 +0900
> Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> > > Yes, anyway we need a way to find loops on histogram/eprobe at last.
> >
> > BTW, what about using similar machanism of "current_kprobe()" to detect
> > the reccursion? As an easy way, prepare a static per-cpu pointer which sets
> > the current eprobe and if the eprobe handler detects that is already set,
> > it may warn (or silently ignore) and reject it.
> > (Of course it is better to detect the loop when user sets the hist-trigger
> > by reverse link)
>
> Thinking more about this, I believe there is a use case for synthetic
> event on a eprobe. Basically:
>
> normal_event -> eprobe (extracts struct data into $dat) -> onmax($dat) -> synthetic event
>
> But I can not come up with any use case of:
>
> eprobe -> synthetic event -> eprobe
>
> or
>
> synthetic event -> eprobe -> synthetic event
>
> That's because once you have an eprobe, you can extract what you want,
> and once you have that synthetic event, you can get the data you want.
>
> Maybe we should prevent the above and allow one eprobe on a synthetic
> event and one synthetic event on an eprobe.
>
> Or just don't prevent it at all, and let the user shoot themselves in
> the foot ;-)
>
> The more I think about this, I'm thinking we just let them shoot
> themselves if they want to.

I agree. Or, at least we can prevent the loop at runtime as I said.
BTW, does synthetic event itself detect and prevent loops? I think
the key point is always synthetic event, so if the loop detector
is implemented, it should be done on the synthetic event.

>
> But I still agree that eprobes should not be attached to kprobes or
> uprobes directly (although they may be able to be attached to a
> synthetic event that is attached to one!)

Yes.

Thank you,


>
> -- Steve


--
Masami Hiramatsu <mhiramat@kernel.org>

\
 
 \ /
  Last update: 2021-08-12 17:07    [W:0.040 / U:0.048 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site