From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752829AbbEFOBr (ORCPT ); Wed, 6 May 2015 10:01:47 -0400 Received: from casper.infradead.org ([85.118.1.10]:49282 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750995AbbEFN7T (ORCPT ); Wed, 6 May 2015 09:59:19 -0400 Message-Id: <20150506135643.653213307@infradead.org> User-Agent: quilt/0.61-1 Date: Wed, 06 May 2015 15:51:42 +0200 From: Peter Zijlstra To: mingo@kernel.org, rusty@rustcorp.com.au, mathieu.desnoyers@efficios.com, oleg@redhat.com, paulmck@linux.vnet.ibm.com, torvalds@linux-foundation.org Cc: linux-kernel@vger.kernel.org, andi@firstfloor.org, rostedt@goodmis.org, tglx@linutronix.de, laijs@cn.fujitsu.com, linux@horizon.com, peterz@infradead.org Subject: [PATCH v6 3/9] rcu: Move lockless_dereference() out of rcupdate.h References: <20150506135139.751304211@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline; filename=peterz-move-lockless_dereference.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I want to use lockless_dereference() from seqlock.h, which would mean including rcupdate.h from it, however rcupdate.h already includes seqlock.h. Avoid this by moving lockless_dereference() into compiler.h. This is somewhat tricky since it uses smp_read_barrier_depends() which isn't available there, but its a CPP macro so we can get away with it. The alternative would be moving it into asm/barrier.h, but that would be updating each arch (I can do if people feel that is more appropriate). Cc: Paul McKenney Signed-off-by: Peter Zijlstra (Intel) --- include/linux/compiler.h | 15 +++++++++++++++ include/linux/rcupdate.h | 15 --------------- 2 files changed, 15 insertions(+), 15 deletions(-) --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -453,6 +453,21 @@ static __always_inline void __write_once (volatile typeof(x) *)&(x); }) #define ACCESS_ONCE(x) (*__ACCESS_ONCE(x)) +/** + * lockless_dereference() - safely load a pointer for later dereference + * @p: The pointer to load + * + * Similar to rcu_dereference(), but for situations where the pointed-to + * object's lifetime is managed by something other than RCU. That + * "something other" might be reference counting or simple immortality. + */ +#define lockless_dereference(p) \ +({ \ + typeof(p) _________p1 = ACCESS_ONCE(p); \ + smp_read_barrier_depends(); /* Dependency order vs. p above. */ \ + (_________p1); \ +}) + /* Ignore/forbid kprobes attach on very low level functions marked by this attribute: */ #ifdef CONFIG_KPROBES # define __kprobes __attribute__((__section__(".kprobes.text"))) --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -650,21 +650,6 @@ static inline void rcu_preempt_sleep_che #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v) /** - * lockless_dereference() - safely load a pointer for later dereference - * @p: The pointer to load - * - * Similar to rcu_dereference(), but for situations where the pointed-to - * object's lifetime is managed by something other than RCU. That - * "something other" might be reference counting or simple immortality. - */ -#define lockless_dereference(p) \ -({ \ - typeof(p) _________p1 = ACCESS_ONCE(p); \ - smp_read_barrier_depends(); /* Dependency order vs. p above. */ \ - (_________p1); \ -}) - -/** * rcu_assign_pointer() - assign to RCU-protected pointer * @p: pointer to assign to * @v: value to assign (publish)