Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935541AbYBMWH7 (ORCPT ); Wed, 13 Feb 2008 17:07:59 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932401AbYBMWF0 (ORCPT ); Wed, 13 Feb 2008 17:05:26 -0500 Received: from e34.co.us.ibm.com ([32.97.110.152]:44649 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933786AbYBMWFX (ORCPT ); Wed, 13 Feb 2008 17:05:23 -0500 Date: Wed, 13 Feb 2008 14:05:15 -0800 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: shemminger@vyatta.com, davem@davemloft.net, netdev@vger.kernel.org, dipankar@in.ibm.com, ego@in.ibm.com, herbert@gondor.apana.org.au, akpm@linux-foundation.org Subject: [PATCH 2/2] add rcu_assign_index() if ever needed Message-ID: <20080213220515.GA10642@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20080213220024.GA30729@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080213220024.GA30729@linux.vnet.ibm.com> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2041 Lines: 52 Hello again! This is a speculative patch that as far as I can tell is not yet required. If anyone applies RCU to a data structure allocated out of an array, using array indexes in place of pointers to link the array elements together, then the rcu_assign_index() function in this patch will be needed to assign a given element's array index to the RCU-traversed index. The implementation is exactly that of the old rcu_assign_pointer(), so is extremely well tested. The existing rcu_assign_pointer() will emit a compiler warning in cases where rcu_assign_index() is required. Signed-off-by: Paul E. McKenney --- rcupdate.h | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff -urpNa -X dontdiff linux-2.6.24-rap/include/linux/rcupdate.h linux-2.6.24-rai/include/linux/rcupdate.h --- linux-2.6.24-rap/include/linux/rcupdate.h 2008-02-13 13:36:47.000000000 -0800 +++ linux-2.6.24-rai/include/linux/rcupdate.h 2008-02-13 10:55:40.000000000 -0800 @@ -286,6 +286,24 @@ extern struct lockdep_map rcu_lock_map; }) /** + * rcu_assign_index - assign (publicize) a index of a newly + * initialized array elementg that will be dereferenced by RCU + * read-side critical sections. Returns the value assigned. + * + * Inserts memory barriers on architectures that require them + * (pretty much all of them other than x86), and also prevents + * the compiler from reordering the code that initializes the + * structure after the index assignment. More importantly, this + * call documents which indexes will be dereferenced by RCU read-side + * code. + */ + +#define rcu_assign_index(p, v) ({ \ + smp_wmb(); \ + (p) = (v); \ + }) + +/** * synchronize_sched - block until all CPUs have exited any non-preemptive * kernel code sequences. * -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/