[PATCH 1/2] v3.2-rc1-52e4c2a05-rt1 fix for compile break

[PATCH 1/2] v3.2-rc1-52e4c2a05-rt1 fix for compile break

[John Kacur]

kernel/rcutorture.c:492: error: ‘synchronize_rcu_bh’ undeclared here (not in a function)

In CONFIG_PREEMPT_RT_FULL
doesn't cover function pointer assignment unless we remove the brackets.

Compile-tested.

Signed-off-by: John Kacur <jkacur@redhat.com>
---
 include/linux/rcutree.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 800b840..6e503a3 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -60,7 +60,7 @@ static inline void exit_rcu(void)
 #ifndef CONFIG_PREEMPT_RT_FULL
 extern void synchronize_rcu_bh(void);
 #else
-# define synchronize_rcu_bh()	synchronize_rcu()
+# define synchronize_rcu_bh	synchronize_rcu
 #endif
 extern void synchronize_sched_expedited(void);
 extern void synchronize_rcu_expedited(void);
-- 
1.7.2.3

[PATCH 2/2] Compile error with allmodconfig and CONFIG_PREEMPT_RT_FULL=y

[John Kacur]

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@redhat.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);
 
 /*
  * Called with bh and local interrupts disabled. For full RT cpu must
-- 
1.7.2.3

Re: [PATCH 2/2] Compile error with allmodconfig and CONFIG_PREEMPT_RT_FULL=y

[Paul E. McKenney]

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@redhat.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?

With that change,

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Not yet ready for mainline, because mainline does not yet have
in_serving_softirq().  Therefore not queued for -rcu.

							Thanx, Paul

>  /*
>   * Called with bh and local interrupts disabled. For full RT cpu must
> -- 
> 1.7.2.3
> 

Re: [PATCH 2/2] Compile error with allmodconfig and CONFIG_PREEMPT_RT_FULL=y

[John Kacur]

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@redhat.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?

> 
> With that change,
> 
> Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> 
> Not yet ready for mainline, because mainline does not yet have
> in_serving_softirq().  Therefore not queued for -rcu.
> 
> 							Thanx, Paul
> 
> >  /*
> >   * Called with bh and local interrupts disabled. For full RT cpu must

Re: [PATCH 2/2] Compile error with allmodconfig and CONFIG_PREEMPT_RT_FULL=y

[Paul E. McKenney]

On Mon, Nov 14, 2011 at 06:39:47PM +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@redhat.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?

No idea.  But I do suggest making new ones EXPORT_SYMBOL_GPL.

							Thanx, Paul

> > With that change,
> > 
> > Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > 
> > Not yet ready for mainline, because mainline does not yet have
> > in_serving_softirq().  Therefore not queued for -rcu.
> > 
> > 							Thanx, Paul
> > 
> > >  /*
> > >   * Called with bh and local interrupts disabled. For full RT cpu must
> 

Re: [PATCH 2/2] Compile error with allmodconfig and CONFIG_PREEMPT_RT_FULL=y

[Steven Rostedt]

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@redhat.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

Re: [PATCH 2/2] Compile error with allmodconfig and CONFIG_PREEMPT_RT_FULL=y

[John Kacur]

On Mon, Nov 14, 2011 at 9:51 PM, Steven Rostedt <rostedt@goodmis.org> wrote:
>
> 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@redhat.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


That's a great explanation - thanks

John Kacur

Re: [PATCH 2/2] Compile error with allmodconfig and CONFIG_PREEMPT_RT_FULL=y

[Mike Galbraith]

On Mon, 2011-11-14 at 15:51 -0500, Steven Rostedt wrote:
> 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@redhat.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.

EXPORT_SYMBOL_GPL(migrate_disable) alone screws nVidia users, no?

I have an RT user who has no other viable choice than nVidia.  If the
above is true, that user will end up stuck at 2.6.33-rt until we get a
driver that actually works... or they deem linux to be a non-solution.

	-Mike

Re: [PATCH 2/2] Compile error with allmodconfig and CONFIG_PREEMPT_RT_FULL=y

[Steven Rostedt]

On Tue, 2011-11-15 at 06:22 +0100, Mike Galbraith wrote:

> > If we go that route, we might as well make everything
> > EXPORT_SYMBOL_GPL(), and be damn to those that use nVidia.
> 
> EXPORT_SYMBOL_GPL(migrate_disable) alone screws nVidia users, no?
> 
> I have an RT user who has no other viable choice than nVidia.  If the
> above is true, that user will end up stuck at 2.6.33-rt until we get a
> driver that actually works... or they deem linux to be a non-solution.

Right, migrate_disable() should not have been an EXPORT_SYMBOL_GPL(), as
it is a helper functions that is also exported as EXPORT_SYMBOL(). It
shouldn't be called directly anyway, even by code in the kernel proper.

-- Steve

Re: [PATCH 2/2] Compile error with allmodconfig and CONFIG_PREEMPT_RT_FULL=y

[Mike Galbraith]

On Tue, 2011-11-15 at 07:23 -0500, Steven Rostedt wrote:

> Right, migrate_disable() should not have been an EXPORT_SYMBOL_GPL(), as
> it is a helper functions that is also exported as EXPORT_SYMBOL(). It
> shouldn't be called directly anyway, even by code in the kernel proper.

Ah.  Doesn't matter though.  I downloaded their latest, tried to build
it with EXPORT_SYMBOL(migrate_enable/disable) ..

FATAL: modpost: GPL-incompatible module nvidia.ko uses GPL-only symbol '__rt_mutex_init'

With that exported, the thing builds and runs, but rt_mutex_foo exports
appear to be intentionally GPL only, so it's "go fish" for nVidia.

	-Mike

Re: [PATCH 2/2] Compile error with allmodconfig and CONFIG_PREEMPT_RT_FULL=y

[Mike Galbraith]

On Tue, 2011-11-15 at 14:27 +0100, Mike Galbraith wrote:

> With that exported, the thing builds and runs, but rt_mutex_foo exports
> appear to be intentionally GPL only, so it's "go fish" for nVidia.

BTW, if you poke that nVidia beast right, it'll keep you locked in
kernel IPI-ing every CPU as fast as we can do that for up to a full
second :>  The only thing I ever found that can match that is ext4.

	-Mike

Re: [PATCH 2/2] Compile error with allmodconfig and CONFIG_PREEMPT_RT_FULL=y

[Mike Galbraith]

On Tue, 2011-11-15 at 14:27 +0100, Mike Galbraith wrote:
> On Tue, 2011-11-15 at 07:23 -0500, Steven Rostedt wrote:
> 
> > Right, migrate_disable() should not have been an EXPORT_SYMBOL_GPL(), as
> > it is a helper functions that is also exported as EXPORT_SYMBOL(). It
> > shouldn't be called directly anyway, even by code in the kernel proper.
> 
> Ah.  Doesn't matter though.  I downloaded their latest, tried to build
> it with EXPORT_SYMBOL(migrate_enable/disable) ..
> 
> FATAL: modpost: GPL-incompatible module nvidia.ko uses GPL-only symbol '__rt_mutex_init'
> 
> With that exported, the thing builds and runs, but rt_mutex_foo exports
> appear to be intentionally GPL only, so it's "go fish" for nVidia.

Bah.  I checked the crusty old hack for crusty old driver, and it still
works just fine with a trivial define.  It'd probably work better if it
didn't need cheezy raw_* hacks, but then it'd probably work better if it
was GPL too ;-)

	-Mike

Re: [PATCH 1/2] v3.2-rc1-52e4c2a05-rt1 fix for compile break

[Paul E. McKenney]

On Mon, Nov 14, 2011 at 02:44:42AM +0100, John Kacur wrote:
> kernel/rcutorture.c:492: error: ‘synchronize_rcu_bh’ undeclared here (not in a function)
> 
> In CONFIG_PREEMPT_RT_FULL
> doesn't cover function pointer assignment unless we remove the brackets.
> 
> Compile-tested.

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

I have not yet queued this because mainline does not yet fold RCU and
RCU-bh together.

							Thanx, Paul

> Signed-off-by: John Kacur <jkacur@redhat.com>
> ---
>  include/linux/rcutree.h |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
> index 800b840..6e503a3 100644
> --- a/include/linux/rcutree.h
> +++ b/include/linux/rcutree.h
> @@ -60,7 +60,7 @@ static inline void exit_rcu(void)
>  #ifndef CONFIG_PREEMPT_RT_FULL
>  extern void synchronize_rcu_bh(void);
>  #else
> -# define synchronize_rcu_bh()	synchronize_rcu()
> +# define synchronize_rcu_bh	synchronize_rcu
>  #endif
>  extern void synchronize_sched_expedited(void);
>  extern void synchronize_rcu_expedited(void);
> -- 
> 1.7.2.3
> 

Re: [PATCH 1/2] v3.2-rc1-52e4c2a05-rt1 fix for compile break

[Steven Rostedt]

On Mon, 2011-11-14 at 02:44 +0100, John Kacur wrote:
> kernel/rcutorture.c:492: error: ‘synchronize_rcu_bh’ undeclared here (not in a function)
> 
> In CONFIG_PREEMPT_RT_FULL
> doesn't cover function pointer assignment unless we remove the brackets.

John,

Please write better change logs. Do not assume that people are looking
at the patch while looking at the logs. I mostly read change logs as
"git log" which doesn't include the changes, and most other developers
do this too. The above sentence does not make any real sense.

Something like:

synchronize_rcu_bh() is not just called as a normal function, but can
also be referenced as a function pointer. When CONFIG_PREEMPT_RT_FULL is
enabled, synchronize_rcu_bh() is defined as synchronize_rcu(), but needs
to be defined without the parenthesis because the compiler will complain
when synchronize_rcu_bh is referenced as a function pointer and not a
function.

-- Steve



> 
> Compile-tested.
> 
> Signed-off-by: John Kacur <jkacur@redhat.com>
> ---
>  include/linux/rcutree.h |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
> index 800b840..6e503a3 100644
> --- a/include/linux/rcutree.h
> +++ b/include/linux/rcutree.h
> @@ -60,7 +60,7 @@ static inline void exit_rcu(void)
>  #ifndef CONFIG_PREEMPT_RT_FULL
>  extern void synchronize_rcu_bh(void);
>  #else
> -# define synchronize_rcu_bh()	synchronize_rcu()
> +# define synchronize_rcu_bh	synchronize_rcu
>  #endif
>  extern void synchronize_sched_expedited(void);
>  extern void synchronize_rcu_expedited(void);