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

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Message-ID: <20161121170612.GT26852@two.firstfloor.org>
Date:   Mon, 21 Nov 2016 09:06:13 -0800
From:   Andi Kleen <andi@...stfloor.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Jiri Olsa <jolsa@...hat.com>, Steven Rostedt <rostedt@...dmis.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Andi Kleen <andi@...stfloor.org>,
        Jan Stancek <jstancek@...hat.com>
Subject: Re: [BUG] msr-trace.h:42 suspicious rcu_dereference_check() usage!

> > it got away with attached change.. but this rcu logic
> > is far beyond me, so it's just wild guess.. ;-)
> 
> I think I prefer something like the below, that only annotates the one
> RDMSR in question, instead of all of them.

It would be far better to just fix trace points that they always work.

This whole thing is a travesty: we have tens of thousands of lines of code in
ftrace to support tracing in NMIs, but then "debug features"[1] like
this come around and make trace points unusable for far more code than
just the NMI handlers.

-Andi

[1] unclear what they  actually "debug" here.