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From: Steven Rostedt <rostedt@goodmis.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Alexei Starovoitov <ast@kernel.org>, paulmck <paulmck@kernel.org>,
	"Joel Fernandes, Google" <joel@joelfernandes.org>,
	Frederic Weisbecker <frederic@kernel.org>,
	Jason Wessel <jason.wessel@windriver.com>
Subject: Re: Instrumentation and RCU
Date: Tue, 10 Mar 2020 11:46:57 -0400
Message-ID: <20200310114657.099122fd@gandalf.local.home> (raw)
In-Reply-To: <450878559.23455.1583854311078.JavaMail.zimbra@efficios.com>

On Tue, 10 Mar 2020 11:31:51 -0400 (EDT)
Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:

> I think there are two distinct problems we are trying to solve here,
> and it would be good to spell them out to see which pieces of technical
> solution apply to which.
> 
> Problem #1) Tracer invoked from partially initialized kernel context
> 
>   - Moving the early/late entry/exit points into sections invisible from
>     instrumentation seems to make tons of sense for this.
> 
> Problem #2) Tracer recursion
> 
>   - I'm much less convinced that hiding entry points from instrumentation
>     works for this. As an example, with the isntr_begin/end() approach you
>     propose above, as soon as you have a tracer recursing into itself because
>     something below do_stuff() has been instrumented, having hidden the entry
>     point did not help at all.
> 
> So I would be tempted to use the "hide entry/exit points" with explicit
> instr begin/end annotation to solve Problem #1, but I'm still thinking there
> is value in the per recursion context "in_tracing" flag to prevent tracer
> recursion.

The only recursion issue that I've seen discussed is breakpoints. And
that's outside of the tracer infrastructure. Basically, if someone added a
breakpoint for a kprobe on something that gets called in the int3 code
before kprobes is called we have (let's say rcu_nmi_enter()):


 rcu_nmi_enter();
  <int3>
     do_int3() {
        rcu_nmi_enter();
          <int3>
             do_int3();
                [..]

Where would a "in_tracer" flag help here? Perhaps a "in_breakpoint" could?

-- Steve

  reply index

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-09 17:02 Thomas Gleixner
2020-03-09 18:15 ` Steven Rostedt
2020-03-09 18:42   ` Joel Fernandes
2020-03-09 19:07     ` Steven Rostedt
2020-03-09 19:20       ` Mathieu Desnoyers
2020-03-16 15:02       ` Joel Fernandes
2020-03-09 18:59   ` Thomas Gleixner
2020-03-10  8:09     ` Masami Hiramatsu
2020-03-10 11:43       ` Thomas Gleixner
2020-03-10 15:31         ` Mathieu Desnoyers
2020-03-10 15:46           ` Steven Rostedt [this message]
2020-03-10 16:21             ` Mathieu Desnoyers
2020-03-11  0:18               ` Masami Hiramatsu
2020-03-11  0:37                 ` Mathieu Desnoyers
2020-03-11  7:48                   ` Masami Hiramatsu
2020-03-10 16:06         ` Masami Hiramatsu
2020-03-12 13:53         ` Peter Zijlstra
2020-03-10 15:24       ` Mathieu Desnoyers
2020-03-10 17:05       ` Daniel Thompson
2020-03-09 18:37 ` Mathieu Desnoyers
2020-03-09 18:44   ` Steven Rostedt
2020-03-09 18:52     ` Mathieu Desnoyers
2020-03-09 19:09       ` Steven Rostedt
2020-03-09 19:25         ` Mathieu Desnoyers
2020-03-09 19:52   ` Thomas Gleixner
2020-03-10 15:03     ` Mathieu Desnoyers
2020-03-10 16:48       ` Thomas Gleixner
2020-03-10 17:40         ` Mathieu Desnoyers
2020-03-10 18:31           ` Thomas Gleixner
2020-03-10 18:37             ` Mathieu Desnoyers
2020-03-10  1:40   ` Alexei Starovoitov
2020-03-10  8:02     ` Thomas Gleixner
2020-03-10 16:54     ` Paul E. McKenney
2020-03-17 17:56     ` Joel Fernandes
2020-03-09 20:18 ` Peter Zijlstra
2020-03-09 20:47 ` Paul E. McKenney
2020-03-09 20:58   ` Steven Rostedt
2020-03-09 21:25     ` Paul E. McKenney
2020-03-09 23:52   ` Frederic Weisbecker
2020-03-10  2:26     ` Paul E. McKenney
2020-03-10 15:13   ` Mathieu Desnoyers
2020-03-10 16:49     ` Paul E. McKenney
2020-03-10 17:22       ` Mathieu Desnoyers
2020-03-10 17:26         ` Paul E. McKenney

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