From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757742AbaEPQH7 (ORCPT ); Fri, 16 May 2014 12:07:59 -0400 Received: from mail-qc0-f175.google.com ([209.85.216.175]:50570 "EHLO mail-qc0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757437AbaEPQH5 (ORCPT ); Fri, 16 May 2014 12:07:57 -0400 Date: Fri, 16 May 2014 12:07:53 -0400 From: Tejun Heo To: lizefan@huawei.com Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, hannes@cmpxchg.org Subject: [PATCH v2 14/14] cgroup: implement css_tryget() Message-ID: <20140516160753.GD5379@htj.dyndns.org> References: <1399671091-23867-1-git-send-email-tj@kernel.org> <1399671091-23867-15-git-send-email-tj@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1399671091-23867-15-git-send-email-tj@kernel.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >>From 141fdfadf18c10fed33624bbd414fcc0cb74d7ca Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 16 May 2014 11:40:38 -0400 Implement css_tryget() which tries to grab a cgroup_subsys_state's reference as long as it already hasn't reached zero. Combined with the recent css iterator changes to include offline && !released csses during traversal, this can be used to access csses regardless of its online state. v2: Take the new flag CSS_NO_REF into account. Signed-off-by: Tejun Heo Acked-by: Li Zefan Cc: Johannes Weiner --- include/linux/cgroup.h | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index b769999..4afe544 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -113,6 +113,24 @@ static inline void css_get(struct cgroup_subsys_state *css) } /** + * css_tryget - try to obtain a reference on the specified css + * @css: target css + * + * Obtain a reference on @css unless it already has reached zero and is + * being released. This function doesn't care whether @css is on or + * offline. The caller naturally needs to ensure that @css is accessible + * but doesn't have to be holding a reference on it - IOW, RCU protected + * access is good enough for this function. Returns %true if a reference + * count was successfully obtained; %false otherwise. + */ +static inline bool css_tryget(struct cgroup_subsys_state *css) +{ + if (!(css->flags & CSS_NO_REF)) + return percpu_ref_tryget(&css->refcnt); + return true; +} + +/** * css_tryget_online - try to obtain a reference on the specified css if online * @css: target css * -- 1.9.0