From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932866AbbFILdY (ORCPT ); Tue, 9 Jun 2015 07:33:24 -0400 Received: from mail-wg0-f41.google.com ([74.125.82.41]:36350 "EHLO mail-wg0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932774AbbFILdO (ORCPT ); Tue, 9 Jun 2015 07:33:14 -0400 From: Aleksa Sarai To: tj@kernel.org, lizefan@huawei.com, mingo@redhat.com, peterz@infradead.org Cc: richard@nod.at, fweisbec@gmail.com, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org Subject: [PATCH v14 2/4] cgroup, block: implement task_get_css() Date: Tue, 9 Jun 2015 21:32:08 +1000 Message-Id: <1433849530-22845-3-git-send-email-cyphar@cyphar.com> X-Mailer: git-send-email 2.4.2 In-Reply-To: <1433849530-22845-1-git-send-email-cyphar@cyphar.com> References: <1433849530-22845-1-git-send-email-cyphar@cyphar.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Tejun Heo Implement task_get_css() which find and pins the css for the specified task and subsys. As a task is always associated with an online css for every subsystem except while the css_set update is propagating, task_get_css() retries till css_tryget_online() succeeds. Signed-off-by: Tejun Heo Cc: Li Zefan --- include/linux/cgroup.h | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index 82319fb..a593e29 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -354,6 +354,31 @@ static inline struct cgroup_subsys_state *task_css(struct task_struct *task, } /** + * task_get_css - find and get the css for (task, subsys) + * @task: the target task + * @subsys_id: the target subsystem ID + * + * Find the css for the (@task, @subsys_id) combination, increment a + * reference on and return it. This function is guaranteed to return a + * valid css. + */ +static inline struct cgroup_subsys_state * +task_get_css(struct task_struct *task, int subsys_id) +{ + struct cgroup_subsys_state *css; + + rcu_read_lock(); + while (true) { + css = task_css(task, subsys_id); + if (likely(css_tryget_online(css))) + break; + cpu_relax(); + } + rcu_read_unlock(); + return css; +} + +/** * task_css_is_root - test whether a task belongs to the root css * @task: the target task * @subsys_id: the target subsystem ID -- 2.4.2