linux-kernel - Re: [PATCH -tip 1/2] Add "notrace" to RCU function headers used by ftrace.

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Message-ID: <20090825022532.GD7355@linux.vnet.ibm.com>
Date:	Mon, 24 Aug 2009 19:25:32 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josht@...ux.vnet.ibm.com,
	dvhltc@...ibm.com, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org
Subject: Re: [PATCH -tip 1/2] Add "notrace" to RCU function headers used by
	ftrace.

On Mon, Aug 24, 2009 at 10:11:40PM -0400, Steven Rostedt wrote:
> 
> On Mon, 24 Aug 2009, Paul E. McKenney wrote:
> 
> > On Mon, Aug 24, 2009 at 07:38:51PM -0400, Steven Rostedt wrote:
> > > 
> > > On Mon, 24 Aug 2009, Paul E. McKenney wrote:
> > > 
> > > > Both rcu_read_lock_sched_notrace() and rcu_read_unlock_sched_notrace()
> > > > are used by ftrace, and thus need to be marked "notrace".  Unfortunately,
> > > > my naive assumption that gcc would see the inner "notrace" does not hold.
> > > > Kudos to Lai Jiangshan for noting this.
> > > > 
> > > > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > > > ---
> > > >  include/linux/rcupdate.h |    4 ++--
> > > >  1 files changed, 2 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> > > > index ec90fc3..8b4422c 100644
> > > > --- a/include/linux/rcupdate.h
> > > > +++ b/include/linux/rcupdate.h
> > > > @@ -191,7 +191,7 @@ static inline void rcu_read_lock_sched(void)
> > > >  	__acquire(RCU_SCHED);
> > > >  	rcu_read_acquire();
> > > >  }
> > > > -static inline void rcu_read_lock_sched_notrace(void)
> > > > +static inline notrace void rcu_read_lock_sched_notrace(void)
> > > >  {
> > > >  	preempt_disable_notrace();
> > > >  	__acquire(RCU_SCHED);
> > > > @@ -209,7 +209,7 @@ static inline void rcu_read_unlock_sched(void)
> > > >  	__release(RCU_SCHED);
> > > >  	preempt_enable();
> > > >  }
> > > > -static inline void rcu_read_unlock_sched_notrace(void)
> > > > +static inline notrace void rcu_read_unlock_sched_notrace(void)
> > > 
> > > Funny, inlines should not be traced. Is gcc ignoring the inlines here?
> > 
> > Well, that was my line of thinking as well, until Lai Jiangshan set
> > me straight.  Version 4.x of gcc apparently decides on a case-by-case
> > basis.
> 
> Yeah, I've seen gcc do it, but when it does it to static inlines in header 
> files, I just get a feeling to squinge.

Especially when they are as short and simple as those particular
functions were...

							Thanx, Paul
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