linux-kernel - On trace_*_rcuidle functions in modules

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Message-ID: <CALAqxLV4rM74wuzuZ+BkUi+keccxkAxv30N4vrFO7CVQ5vnT1A@mail.gmail.com>
Date:   Tue, 14 Apr 2020 19:20:01 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     paulmck@...nel.org, Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     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>
Subject: On trace_*_rcuidle functions in modules

Hey folks,
  So recently I was looking at converting some drivers to be loadable
modules instead of built-in only, and one of my patches just landed in
-next and started getting build error reports.

It ends up, recently in the merge window, the driver I was converting
to module switched a trace_*() function to trace_*_rcuidle() to fix a
bug.  Now when building as a module, if tracing is configured on, it
can't seem to find the trace_*_rcuidle() symbol.

This is because, as you are aware, we don't declare trace_*_rcuidle
functions in modules - and haven't for quite some time:
  https://lore.kernel.org/lkml/20120905062306.GA14756@leaf/

I wanted to better understand the background rationale for that patch,
to understand if not exporting the rcu_idle_exit and rcu_idle_enter,
calls was because they weren't used or if it was a more intentional
decision to avoid allowing modules to use them.

Would it be reasonable to revisit that patch? Or is there some
recommended alternative solution?

thanks
-john