On Thu, 12 Aug 2021 09:44:39 -0400 Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > On Thu, 12 Aug 2021 20:31:10 +0900 > Masami Hiramatsu <mhiramat@xxxxxxxxxx> 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@xxxxxxxxxx>
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