From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934437AbaH0NPX (ORCPT ); Wed, 27 Aug 2014 09:15:23 -0400 Received: from mail-wg0-f42.google.com ([74.125.82.42]:34978 "EHLO mail-wg0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933270AbaH0NPV (ORCPT ); Wed, 27 Aug 2014 09:15:21 -0400 Date: Wed, 27 Aug 2014 16:15:13 +0300 From: Andreea-Cristina Bernat To: axboe@kernel.dk, linux-kernel@vger.kernel.org Cc: paulmck@linux.vnet.ibm.com Subject: [PATCH] block: genhd: Replace rcu_assign_pointer() with RCU_INIT_POINTER() Message-ID: <20140827131513.GA31290@ada> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org According to RCU_INIT_POINTER()'s block comment 3.a, it can be used if "3. The referenced data structure has already been exposed to readers either at compile time or via rcu_assign_pointer() -and- a. You have not made -any- reader-visible changes to this structure since then". This case fulfills the conditions above because between the rcu_dereference() call and the rcu_assign_pointer() call there is no update of the "part" variable. Therefore, this patch makes the replacement. The following Coccinelle semantic patch was used: @@ identifier v; @@ v = rcu_dereference(...); ... when != rcu_dereference(...); when != v = ...; when != (<+...v...+>)++; when != \(memcpy\|memset\)(...); ( - rcu_assign_pointer + RCU_INIT_POINTER (..., v); | if(...) { ... when != v = ...; - rcu_assign_pointer + RCU_INIT_POINTER (..., v); ... when any } ) Because there are cases where between a “rcu_dereference()” call and a “rcu_assign_pointer()” call might be updates of the value that interests us, the Coccinelle semantic patch ignores them and replaces with "RCU_INIT_POINTER()" only when the update is not happening. Signed-off-by: Andreea-Cristina Bernat --- block/genhd.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/block/genhd.c b/block/genhd.c index 3aec057..f7e29d8 100644 --- a/block/genhd.c +++ b/block/genhd.c @@ -228,7 +228,7 @@ struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector) part = rcu_dereference(ptbl->part[i]); if (part && sector_in_part(part, sector)) { - rcu_assign_pointer(ptbl->last_lookup, part); + RCU_INIT_POINTER(ptbl->last_lookup, part); return part; } } -- 1.9.1