linux-kernel - Re: linux-next: build failure after merge of the rcu tree

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Date:	Fri, 8 Jan 2016 12:54:53 +0800
From:	Boqun Feng <boqun.feng@...il.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	Tejun Heo <tj@...nel.org>,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: linux-next: build failure after merge of the rcu tree

On Thu, Jan 07, 2016 at 08:48:35PM -0800, Paul E. McKenney wrote:
> On Fri, Jan 08, 2016 at 03:08:50PM +1100, Stephen Rothwell wrote:
> > Hi Paul,
> > 
> > On Thu, 7 Jan 2016 19:41:57 -0800 "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> > >
> > > Indeed, I suspect that SRCU might not be the only thing that would like
> > > static per-CPU variables.  ;-)
> > 
> > from include/linux/percpu-defs.h:
> > 
> >  * s390 and alpha modules require percpu variables to be defined as
> >  * weak to force the compiler to generate GOT based external
> >  * references for them.  This is necessary because percpu sections
> >  * will be located outside of the usually addressable area.
> >  *
> >  * This definition puts the following two extra restrictions when
> >  * defining percpu variables.
> >  *
> >  * 1. The symbol must be globally unique, even the static ones.
> >  * 2. Static percpu variables cannot be defined inside a function.
> >  *
> >  * Archs which need weak percpu definitions should define
> >  * ARCH_NEEDS_WEAK_PER_CPU in asm/percpu.h when necessary.
> >  *
> >  * To ensure that the generic code observes the above two
> >  * restrictions, if CONFIG_DEBUG_FORCE_WEAK_PER_CPU is set weak
> >  * definition is used for all cases.
> > 
> > so they can be static, but must be globally unique.

Interesting ;-) Thank you.

> 
> Thank you for the tutorial!  I have updated the patch to use a unique
> name for the srcu_struct added by rcuperf.c.
> 

Plus a comment for DEFINE_STATIC_SRCU saying srcu can be defined as
static but must have a unique name for this reason?

Regards,
Boqun

> 							Thanx, Paul
> 

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