From: Masami Hiramatsu <mhiramat@kernel.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: "Tzvetomir Stoyanov (VMware)" <tz.stoyanov@gmail.com>,
linux-trace-devel@vger.kernel.org, linux-kernel@vger.kernel.org,
tom.zanussi@linux.intel.com
Subject: Re: [PATCH v4] [RFC] trace: Add kprobe on tracepoint
Date: Fri, 13 Aug 2021 00:06:59 +0900 [thread overview]
Message-ID: <20210813000659.48eafbcfeeaa30adcc8a5363@kernel.org> (raw)
In-Reply-To: <20210812094439.56303efa@oasis.local.home>
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>
next prev parent reply other threads:[~2021-08-12 15:07 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-11 14:14 [PATCH v4] [RFC] trace: Add kprobe on tracepoint Tzvetomir Stoyanov (VMware)
2021-08-11 15:03 ` Masami Hiramatsu
2021-08-11 15:22 ` Steven Rostedt
2021-08-12 1:27 ` Masami Hiramatsu
2021-08-12 3:46 ` Steven Rostedt
2021-08-12 9:44 ` Masami Hiramatsu
2021-08-12 11:14 ` Masami Hiramatsu
2021-08-12 4:02 ` Steven Rostedt
2021-08-12 11:15 ` Masami Hiramatsu
2021-08-12 11:31 ` Masami Hiramatsu
2021-08-12 13:44 ` Steven Rostedt
2021-08-12 15:06 ` Masami Hiramatsu [this message]
2021-08-12 15:44 ` Masami Hiramatsu
2021-08-16 21:40 ` Steven Rostedt
2021-08-17 11:52 ` Masami Hiramatsu
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