linux-kernel - Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods

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Message-Id: <20170712190006.GA28034@linux.vnet.ibm.com>
Date:   Wed, 12 Jul 2017 12:00:06 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Frederic Weisbecker <fweisbec@...il.com>,
        Christoph Lameter <cl@...ux.com>,
        "Li, Aubrey" <aubrey.li@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Aubrey Li <aubrey.li@...el.com>, tglx@...utronix.de,
        len.brown@...el.com, rjw@...ysocki.net, tim.c.chen@...ux.intel.com,
        arjan@...ux.intel.com, yang.zhang.wz@...il.com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods

On Wed, Jul 12, 2017 at 11:53:06AM -0700, Paul E. McKenney wrote:
> On Wed, Jul 12, 2017 at 07:46:42PM +0200, Peter Zijlstra wrote:
> > On Wed, Jul 12, 2017 at 08:56:51AM -0700, Paul E. McKenney wrote:
> > > Very good, I have queued the patch below.  I left out the removal of
> > > the export as I need to work out why the export was there.  If it turns
> > > out not to be needed, I will remove the related ones as well.
> > 
> > 'git grep rcu_idle_enter' shows no callers other than
> > kernel/sched/idle.c. Which seems a clear indication its not needed.
> > 
> > You also have to ask yourself, do I want joe module author to ever call
> > this. To which I suspect the answer is: hell no ;-)
> 
> The other question is "why did I do this in the first place".
> 
> The only case where there will turn out to have been a still-valid reason
> is if I remove it without checking first.  ;-)

And I have now checked.  Please see below.

							Thanx, Paul

------------------------------------------------------------------------

commit 31b2fd02abe5f036d7e83461bd19bbca3636d62e
Author: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Date:   Wed Jul 12 11:55:21 2017 -0700

    rcu: Remove exports from rcu_idle_exit() and rcu_idle_enter()
    
    The rcu_idle_exit() and rcu_idle_enter() functions are exported because
    they were originally used by RCU_NONIDLE(), which was intended to
    be usable from modules.  However, RCU_NONIDLE() now instead uses
    rcu_irq_enter_irqson() and rcu_irq_exit_irqson(), which are not
    exported, and there have been no complaints.
    
    This commit therefore removes the exports from rcu_idle_exit() and
    rcu_idle_enter().
    
    Reported-by: Peter Zijlstra <peterz@...radead.org>
    Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 0798d2585e87..860d1c147606 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -843,7 +843,6 @@ void rcu_idle_enter(void)
 	RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_idle_enter() invoked with irqs enabled!!!");
 	rcu_eqs_enter(false);
 }
-EXPORT_SYMBOL_GPL(rcu_idle_enter);
 
 #ifdef CONFIG_NO_HZ_FULL
 /**
@@ -976,7 +975,6 @@ void rcu_idle_exit(void)
 	rcu_eqs_exit(false);
 	local_irq_restore(flags);
 }
-EXPORT_SYMBOL_GPL(rcu_idle_exit);
 
 #ifdef CONFIG_NO_HZ_FULL
 /**