From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: linux-next: build failure after merge of the rcu tree Date: Fri, 8 Jan 2016 10:57:27 -0500 Message-ID: <20160108155727.GP1898@mtj.duckdns.org> References: <20160107195725.3a130b4d@canb.auug.org.au> <20160107180244.GR3818@linux.vnet.ibm.com> <20160108071932.060a9bcc@canb.auug.org.au> <20160107205220.GU3818@linux.vnet.ibm.com> <20160108013631.GA11410@fixme-laptop.cn.ibm.com> <20160108034157.GZ3818@linux.vnet.ibm.com> <20160108150850.1ec97e78@canb.auug.org.au> <20160108044835.GB3818@linux.vnet.ibm.com> <20160108045453.GB4300@fixme-laptop.cn.ibm.com> <20160108155341.GC3818@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20160108155341.GC3818@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org To: "Paul E. McKenney" Cc: Boqun Feng , Stephen Rothwell , linux-next@vger.kernel.org, linux-kernel@vger.kernel.org, Christoph Lameter List-Id: linux-next.vger.kernel.org On Fri, Jan 08, 2016 at 07:53:41AM -0800, Paul E. McKenney wrote: > commit 61822ff81839ee3c5b6094ce348944d972b87892 > Author: Paul E. McKenney > Date: Fri Jan 8 07:43:50 2016 -0800 > > rcu: Document unique-name limitation for DEFINE_STATIC_SRCU() > > SRCU uses per-CPU variables, and DEFINE_STATIC_SRCU() uses a static > per-CPU variable. However, per-CPU variables have significant > restrictions, for example, names of per-CPU variables must be globally > unique, even if declared static. These restrictions carry over to > DEFINE_STATIC_SRCU(), and this commit therefore documents these > restrictions. > > Reported-by: Stephen Rothwell > Reported-by: kbuild test robot > Suggested-by: Boqun Feng > Signed-off-by: Paul E. McKenney > > diff --git a/include/linux/srcu.h b/include/linux/srcu.h > index f5f80c5643ac..dc8eb63c6568 100644 > --- a/include/linux/srcu.h > +++ b/include/linux/srcu.h > @@ -99,8 +99,23 @@ void process_srcu(struct work_struct *work); > } > > /* > - * define and init a srcu struct at build time. > - * dont't call init_srcu_struct() nor cleanup_srcu_struct() on it. > + * Define and initialize a srcu struct at build time. > + * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it. > + * > + * Note that although DEFINE_STATIC_SRCU() hides the name from other > + * files, the per-CPU variable rules nevertheless require that the > + * chosen name be globally unique. These rules also prohibit use of > + * DEFINE_STATIC_SRCU() within a function. If these rules are too > + * restrictive, declare the srcu_struct manually. For example, in > + * each file: > + * > + * static struct srcu_struct my_srcu; > + * > + * Then, before the first use of each my_srcu, manually initialize it: > + * > + * init_srcu_struct(&my_srcu); > + * > + * See include/linux/percpu-defs.h for the rules on per-CPU variables. FWIW, Reviewed-by: Tejun Heo Thanks Stephen for posting the rules around static percpu definitions. I wonder whether there is a better way to tell people what's going on. Thanks. -- tejun