From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932900AbcBXFPE (ORCPT ); Wed, 24 Feb 2016 00:15:04 -0500 Received: from e19.ny.us.ibm.com ([129.33.205.209]:46014 "EHLO e19.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757914AbcBXFNA (ORCPT ); Wed, 24 Feb 2016 00:13:00 -0500 X-IBM-Helo: d01dlp02.pok.ibm.com X-IBM-MailFrom: paulmck@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 11/13] rcu: Document unique-name limitation for DEFINE_STATIC_SRCU() Date: Tue, 23 Feb 2016 21:12:48 -0800 Message-Id: <1456290770-18659-11-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 2.5.2 In-Reply-To: <20160224051221.GA17099@linux.vnet.ibm.com> References: <20160224051221.GA17099@linux.vnet.ibm.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16022405-0057-0000-0000-0000038309BE Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Reviewed-by: Tejun Heo --- include/linux/srcu.h | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) 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. */ #define __DEFINE_SRCU(name, is_static) \ static DEFINE_PER_CPU(struct srcu_struct_array, name##_srcu_array);\ -- 2.5.2