Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Wed, 15 Apr 2020 16:41:16 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     John Stultz <john.stultz@linaro.org>
Cc:     paulmck@kernel.org, Josh Triplett <josh@joshtriplett.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Saravana Kannan <saravanak@google.com>,
        Todd Kjos <tkjos@google.com>, Stephen Boyd <sboyd@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: On trace_*_rcuidle functions in modules
Message-ID: <20200415164116.40564f2c@gandalf.local.home>
In-Reply-To: <CALAqxLU26PVFPSza5GceSF6gTVdzo_2D3G0dBp0KZXvAWFUktA@mail.gmail.com>
References: <CALAqxLV4rM74wuzuZ+BkUi+keccxkAxv30N4vrFO7CVQ5vnT1A@mail.gmail.com>
        <20200415085348.5511a5fe@gandalf.local.home>
        <CALAqxLV1A6sOC1GWpFYXeBoDff0+AJgoOYK7NktcTdvX3kvAeg@mail.gmail.com>
        <20200415161424.584d07d3@gandalf.local.home>
        <CALAqxLU26PVFPSza5GceSF6gTVdzo_2D3G0dBp0KZXvAWFUktA@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, 15 Apr 2020 13:17:53 -0700
John Stultz <john.stultz@linaro.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