linux-kernel - Re: [PATCH RFC tip/core/rcu 02/23] rcu: add _

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Date:	Thu, 13 May 2010 14:48:18 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Matt Helsley <matthltc@...ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	dvhltc@...ibm.com, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com,
	Arnd Bergmann <arnd@...db.de>,
	Christopher Li <sparse@...isli.org>
Subject: Re: [PATCH RFC tip/core/rcu 02/23] rcu: add __rcu API for later
 sparse checking

On Thu, May 13, 2010 at 01:53:07PM -0700, Matt Helsley wrote:
> On Wed, May 12, 2010 at 02:33:21PM -0700, Paul E. McKenney wrote:
> > This commit defines an __rcu API, but provides only vacuous definitions
> > for it.  This breaks dependencies among most of the subsequent patches,
> > allowing them to reach mainline asynchronously via whatever trees are
> > appropriate.
> 
> Seems like a good plan to me.
> 
> I know it's not the right time to push it but I am curious to see what,
> approximately, you expect a non-vacuous __rcu definition to look like.
> (i.e. when it's being run through sparse)

Patch 6 of this series defines the sparse magic and the rcu_dereference()
checks that do this.  But yes, there are dependencies among these patches.

							Thanx, Paul

> Cheers,
> 	-Matt Helsley
> 
> > 
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > Cc: Christopher Li <sparse@...isli.org>
> > Cc: Josh Triplett <josh@...htriplett.org>
> > ---
> >  include/linux/compiler.h |    2 ++
> >  1 files changed, 2 insertions(+), 0 deletions(-)
> > 
> > diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> > index a5a472b..c1a62c5 100644
> > --- a/include/linux/compiler.h
> > +++ b/include/linux/compiler.h
> > @@ -16,6 +16,7 @@
> >  # define __release(x)	__context__(x,-1)
> >  # define __cond_lock(x,c)	((c) ? ({ __acquire(x); 1; }) : 0)
> >  # define __percpu	__attribute__((noderef, address_space(3)))
> > +# define __rcu
> >  extern void __chk_user_ptr(const volatile void __user *);
> >  extern void __chk_io_ptr(const volatile void __iomem *);
> >  #else
> > @@ -34,6 +35,7 @@ extern void __chk_io_ptr(const volatile void __iomem *);
> >  # define __release(x) (void)0
> >  # define __cond_lock(x,c) (c)
> >  # define __percpu
> > +# define __rcu
> >  #endif
> > 
> >  #ifdef __KERNEL__
> > -- 
> > 1.7.0.6
> > 
> > --
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