From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752815AbaKQVPz (ORCPT ); Mon, 17 Nov 2014 16:15:55 -0500 Received: from mail-qg0-f48.google.com ([209.85.192.48]:35659 "EHLO mail-qg0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751923AbaKQVPy (ORCPT ); Mon, 17 Nov 2014 16:15:54 -0500 Date: Mon, 17 Nov 2014 16:15:46 -0500 From: Tejun Heo To: Jens Axboe Cc: linux-kernel@vger.kernel.org, Vivek Goyal , Li Zefan Subject: [PATCH block/for-next 3/4] cgroup, block: implement task_get_css() and use it in bio_associate_current() Message-ID: <20141117211546.GF23126@htj.dyndns.org> References: <20141117211321.GD23126@htj.dyndns.org> <20141117211357.GE23126@htj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141117211357.GE23126@htj.dyndns.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 bio_associate_current() currently open codes task_css() and css_tryget_online() to find and pin $current's blkcg css. Abstract it into task_get_css() which is implemented from cgroup side. 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. This is a cleanup and shouldn't lead to noticeable behavior changes. Signed-off-by: Tejun Heo Cc: Li Zefan Cc: Jens Axboe Cc: Vivek Goyal --- Hello, This one can be routed through either cgroup or block tree but I think it'd be easier to route this through block as there will be more block changes in the area. Thanks. block/bio.c | 11 +---------- include/linux/cgroup.h | 25 +++++++++++++++++++++++++ 2 files changed, 26 insertions(+), 10 deletions(-) --- a/block/bio.c +++ b/block/bio.c @@ -1997,7 +1997,6 @@ EXPORT_SYMBOL(bioset_create_nobvec); int bio_associate_current(struct bio *bio) { struct io_context *ioc; - struct cgroup_subsys_state *css; if (bio->bi_ioc) return -EBUSY; @@ -2006,17 +2005,9 @@ int bio_associate_current(struct bio *bi if (!ioc) return -ENOENT; - /* acquire active ref on @ioc and associate */ get_io_context_active(ioc); bio->bi_ioc = ioc; - - /* associate blkcg if exists */ - rcu_read_lock(); - css = task_css(current, blkio_cgrp_id); - if (css && css_tryget_online(css)) - bio->bi_css = css; - rcu_read_unlock(); - + bio->bi_css = task_get_css(current, blkio_cgrp_id); return 0; } --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -748,6 +748,31 @@ static inline struct cgroup_subsys_state } /** + * 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