linux-kernel - Re: [BUG] msr-trace.h:42 suspicious rcu_dereference

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Message-ID: <20161121140641.1b0d4c8a@gandalf.local.home>
Date:   Mon, 21 Nov 2016 14:06:41 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Andi Kleen <andi@...stfloor.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Jiri Olsa <jolsa@...hat.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Jan Stancek <jstancek@...hat.com>
Subject: Re: [BUG] msr-trace.h:42 suspicious rcu_dereference_check() usage!

On Mon, 21 Nov 2016 10:37:00 -0800
Andi Kleen <andi@...stfloor.org> wrote:

> Ok so how should tracing in idle code work then in your opinion?

As I suggested already. If we can get a light weight rcu_is_watching()
then we can do the rcu_idle work when needed, and not when we don't
need it. Sure this will add more branches, but that's still cheaper
than popf.

-- Steve