linux-kernel - Re: [PATCH v2 03/11] sched,idle,rcu: Push rcu

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Date:   Wed, 2 Sep 2020 09:08:00 +0200
From:   peterz@...radead.org
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org, will@...nel.org,
        npiggin@...il.com, elver@...gle.com, jgross@...e.com,
        paulmck@...nel.org, rostedt@...dmis.org, rjw@...ysocki.net,
        svens@...ux.ibm.com, tglx@...utronix.de,
        mathieu.desnoyers@...icios.com
Subject: Re: [PATCH v2 03/11] sched,idle,rcu: Push rcu_idle deeper into the
 idle path

On Thu, Aug 27, 2020 at 06:30:01PM -0400, Joel Fernandes wrote:
> On Thu, Aug 27, 2020 at 09:47:48AM +0200, peterz@...radead.org wrote:

> > All trace_*_rcuidle() and RCU_NONIDLE() usage is a bug IMO.
> > 
> > Ideally RCU-trace goes away too.
> 
> I was thinking that unless the rcu_idle_enter/exit calls coincide with points
> in the kernel where instrumentation is not allowed, there is always a chance
> somebody wants to use tracepoints after rcu_idle_enter or before exit. In
> this case, trace_*_rcuidle() is unavoidable unless you can move the
> rcu_idle_enter/exit calls deeper as you are doing.
> 
> Maybe objtool can help with that?

The eventual goal is to mark idle code noinstr too. There's more work
before we can do that.