From patchwork Tue Dec 8 09:09:04 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Herbert Xu X-Patchwork-Id: 553830 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id EBF0B1402BD for ; Tue, 8 Dec 2015 20:09:37 +1100 (AEDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756187AbbLHJJd (ORCPT ); Tue, 8 Dec 2015 04:09:33 -0500 Received: from helcar.hengli.com.au ([209.40.204.226]:45802 "EHLO helcar.hengli.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756098AbbLHJJb (ORCPT ); Tue, 8 Dec 2015 04:09:31 -0500 Received: from gondolin.me.apana.org.au ([192.168.0.6]) by norbury.hengli.com.au with esmtp (Exim 4.80 #3 (Debian)) id 1a6EGs-0006Yb-Dr; Tue, 08 Dec 2015 20:09:18 +1100 Received: from herbert by gondolin.me.apana.org.au with local (Exim 4.80) (envelope-from ) id 1a6EGi-0004bP-QY; Tue, 08 Dec 2015 17:09:08 +0800 Date: Tue, 8 Dec 2015 17:09:04 +0800 From: Herbert Xu To: "David S. Miller" , Thomas Graf , Eric Dumazet , Josh Triplett , "Paul E. McKenney" , netdev@vger.kernel.org Subject: rhashtable: Remove unnecessary wmb for future_tbl Message-ID: <20151208090904.GA17605@gondor.apana.org.au> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org The patch 9497df88ab5567daa001829051c5f87161a81ff0 ("rhashtable: Fix reader/rehash race") added a pair of barriers. In fact the wmb is superfluous because every subsequent write to the old or new hash table uses rcu_assign_pointer, which itself carriers a full barrier prior to the assignment. Therefore we may remove the explicit wmb. Signed-off-by: Herbert Xu Acked-by: Thomas Graf diff --git a/lib/rhashtable.c b/lib/rhashtable.c index 1c624db..d1f94b4 100644 --- a/lib/rhashtable.c +++ b/lib/rhashtable.c @@ -232,9 +232,6 @@ static int rhashtable_rehash_attach(struct rhashtable *ht, */ rcu_assign_pointer(old_tbl->future_tbl, new_tbl); - /* Ensure the new table is visible to readers. */ - smp_wmb(); - spin_unlock_bh(old_tbl->locks); return 0;