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 [thread overview]
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
next prev parent reply other threads:[~2020-03-10 15:47 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-09 17:02 Instrumentation and RCU 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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