linux-kernel - Re: [PATCH] tracepoint: Allow livepatch module add trace event

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Message-ID: <20221114220216.05dd0541@gandalf.local.home>
Date:   Mon, 14 Nov 2022 22:02:16 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Jianlin Lv <iecedge@...il.com>
Cc:     alison.schofield@...el.com, davidgow@...gle.com,
        thunder.leizhen@...wei.com, jianlv@...y.com,
        linux-kernel@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH] tracepoint: Allow livepatch module add trace event

On Tue, 15 Nov 2022 10:38:34 +0800
Jianlin Lv <iecedge@...il.com> wrote:

> On Tue, Nov 15, 2022 at 1:22 AM Steven Rostedt <rostedt@...dmis.org> wrote:
> >
> > On Wed,  2 Nov 2022 16:02:36 +0000
> > Jianlin Lv <iecedge@...il.com> wrote:
> >  
> > > In the case of keeping the system running, the preferred method for
> > > tracing the kernel is dynamic tracing (kprobe), but the drawback of
> > > this method is that events are lost, especially when tracing packages
> > > in the network stack.  
> >
> > I'm not against this change, but the above is where I'm a bit confused. How
> > are events more likely to be lost with kprobes over a static event?  
> 
> We have encountered a case of kprobes missing event, detailed
> information can refer to the following link:
> https://github.com/iovisor/bcc/issues/4198
> 
> Replacing kprobe with ’bpf + raw tracepoint‘,  no missing events occur.
> 

Masami,

What's the reason that kprobes are not re-entrant when using ftrace?

-- Steve