linux-kernel - Re: [PATCH v2] tracing: Fix event probe removal from dynamic events

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Date:   Wed, 13 Oct 2021 07:42:26 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tom Zanussi <zanussi@...nel.org>,
        Tzvetomir Stoyanov <tz.stoyanov@...il.com>,
        Yordan Karadzhov <y.karadz@...il.com>
Subject: Re: [PATCH v2] tracing: Fix event probe removal from dynamic events

On Tue, 12 Oct 2021 12:03:10 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Tue, 12 Oct 2021 23:31:07 +0900
> Masami Hiramatsu <mhiramat@...nel.org> wrote:
> 
> > Hmm, this seems something wrong. Via dynamic_events interface, all the
> > events must be parsed equaly. If you have to pass the attached "system/event"
> > that's something wrong. The dynamic_events interface will accept 
> > 
> > -:[GROUP/]EVENT [optional arguments]
> > 
> > Or
> > 
> > !e:[GROUP/]EVENT [optional arguments]
> > 
> > What did you expect other that these syntax?
> 
> But there are non "optional arguments".
> 
> To create the event probe, we need to send:
> 
>   e:[GROUP/]EVENT system/event [optional arguments]
> 
> Where the "system/event" is what we attach to. Similar to adding a function
> or address to kprobes. Do you not need to add that for deleting a kprobe?

No, since if the GROUP name is given, we can identify the event.

And sorry. I misunderstood your patch, simply I mixed the group/event is
the name of group/event or the attached group/event.

Actually, the dynamic_events delete command is something like wildcard
unless you specify the options.

> 
> That is, if I create a kprobe with:
> 
>   p:myprobe schedule > dynamic_events
> 
> To remove it, don't we need to have:
> 
>   -:myprobe schedule >> dynamic_events

Yes, it is possible. But you can also do

 -:kprobes/myprobe >> dynamic_events 

So, the "schedule" trace point is optional.

Anyway, let me comment on your patch again.

Thank you,


-- 
Masami Hiramatsu <mhiramat@...nel.org>