linux-kernel - Re: On trace_*_rcuidle functions in modules

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Message-ID: <20200415164116.40564f2c@gandalf.local.home>
Date:   Wed, 15 Apr 2020 16:41:16 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     paulmck@...nel.org, Josh Triplett <josh@...htriplett.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Saravana Kannan <saravanak@...gle.com>,
        Todd Kjos <tkjos@...gle.com>, Stephen Boyd <sboyd@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: On trace_*_rcuidle functions in modules

On Wed, 15 Apr 2020 13:17:53 -0700
John Stultz <john.stultz@...aro.org> wrote:

> > Hmm, isn't module code itself synchronized via RCU. Then having module code
> > being called without RCU "watching" could be dangerous?  
> 
> I'm not sure I'm following you here. Could you explain more?

So how does this code get registered to be called as a module? And if it is
registered, I'm guessing it needs to be unregistered too. How would that be
synchronized? Usually, calling synchronize_rcu() is done after
unregistering, but if that code is called without RCU watching, it is
possible synchronize_rcu() can finish before that code is released.

-- Steve