linux-kernel - Re: [PATCH 2/2] Compile error with allmodconfig and CONFIG_PREEMPT_RT

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Date:	Mon, 14 Nov 2011 15:51:11 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	John Kacur <jkacur@...hat.com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	lkml <linux-kernel@...r.kernel.org>,
	rt-users <linux-rt-users@...r.kernel.org>
Subject: Re: [PATCH 2/2] Compile error with allmodconfig and
 CONFIG_PREEMPT_RT_FULL=y

On Mon, 2011-11-14 at 18:39 +0100, John Kacur wrote:
> 
> On Mon, 14 Nov 2011, Paul E. McKenney wrote:
> 
> > On Mon, Nov 14, 2011 at 02:44:43AM +0100, John Kacur wrote:
> > > ERROR: "in_serving_softirq" [net/sched/cls_cgroup.ko] undefined!
> > > 
> > > The above can be fixed by exporting in_serving_softirq
> > > 
> > > Signed-off-by: John Kacur <jkacur@...hat.com>
> > > 
> > > The above patch was originally for 3.0.9-rt25
> > > But I also needed to cherry-pick it for 3.2-rc1-rt1
> > > ---
> > >  kernel/softirq.c |    1 +
> > >  1 files changed, 1 insertions(+), 0 deletions(-)
> > > 
> > > diff --git a/kernel/softirq.c b/kernel/softirq.c
> > > index 3db1d6f..5452432 100644
> > > --- a/kernel/softirq.c
> > > +++ b/kernel/softirq.c
> > > @@ -447,6 +447,7 @@ int in_serving_softirq(void)
> > >  	preempt_enable();
> > >  	return res;
> > >  }
> > > +EXPORT_SYMBOL(in_serving_softirq);
> > 
> > Why not EXPORT_SYMBOL_GPL?
> 
> I have no problem with that, note however that the upstream file has
> 
> EXPORT_SYMBOL(irq_stat);
> EXPORT_SYMBOL(local_bh_disable);
> EXPORT_SYMBOL(_local_bh_enable);
> EXPORT_SYMBOL(local_bh_enable);
> EXPORT_SYMBOL(local_bh_enable_ip);
> EXPORT_SYMBOL(__tasklet_schedule);
> EXPORT_SYMBOL(__tasklet_hi_schedule);
> EXPORT_SYMBOL(__tasklet_hi_schedule_first);
> EXPORT_SYMBOL(tasklet_init);
> EXPORT_SYMBOL(tasklet_kill);
> EXPORT_SYMBOL(__send_remote_softirq);
> EXPORT_SYMBOL(send_remote_softirq);
> 
> Any reason we can't change all of those to EXPORT_SYMBOL_GPL?\\

IIRC, the point behind EXPORT_SYMBOL_GPL() is that, by using the call
you are using something that is a derivative of the code. Basically all
new functionality of the kernel is Linux specific and symbols exported
should be EXPORT_SYMBOL_GPL().

But, I also recall that we did not want to make things that are normal
OS operations under the EXPORT_SYMBOL_GPL(). This would include the
local_bh_enable/disable(), or anything that is called by generic
operations. For example, spin_lock() is not a GPL symbol, and if we add
some new functionality that causes all spin_locks() to call foo_bar(),
we must also make sure foo_bar() is also under just EXPORT_SYMBOL(),
otherwise, we just forced EXPORT_SYMBOL_GPL() on spin_lock().

Some of the above is probably just simple OS operations or are called by
static OS operation functions.

If we go that route, we might as well make everything
EXPORT_SYMBOL_GPL(), and be damn to those that use nVidia.

-- Steve

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