From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qg0-f51.google.com (mail-qg0-f51.google.com [209.85.192.51]) by kanga.kvack.org (Postfix) with ESMTP id ECFF26B00F1 for ; Tue, 6 Jan 2015 14:29:32 -0500 (EST) Received: by mail-qg0-f51.google.com with SMTP id i50so16797198qgf.38 for ; Tue, 06 Jan 2015 11:29:32 -0800 (PST) Received: from mail-qc0-x232.google.com (mail-qc0-x232.google.com. [2607:f8b0:400d:c01::232]) by mx.google.com with ESMTPS id u46si22366909qge.42.2015.01.06.11.29.28 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 06 Jan 2015 11:29:28 -0800 (PST) Received: by mail-qc0-f178.google.com with SMTP id p6so1323642qcv.9 for ; Tue, 06 Jan 2015 11:29:28 -0800 (PST) From: Tejun Heo Subject: [PATCH 04/16] cgroup, block: implement task_get_css() and use it in bio_associate_current() Date: Tue, 6 Jan 2015 14:29:05 -0500 Message-Id: <1420572557-11572-5-git-send-email-tj@kernel.org> In-Reply-To: <1420572557-11572-1-git-send-email-tj@kernel.org> References: <1420572557-11572-1-git-send-email-tj@kernel.org> Sender: owner-linux-mm@kvack.org List-ID: To: axboe@kernel.dk Cc: linux-kernel@vger.kernel.org, jack@suse.cz, hch@infradead.org, hannes@cmpxchg.org, linux-fsdevel@vger.kernel.org, vgoyal@redhat.com, lizefan@huawei.com, cgroups@vger.kernel.org, linux-mm@kvack.org, mhocko@suse.cz, Tejun Heo 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 --- block/bio.c | 11 +---------- include/linux/cgroup.h | 25 +++++++++++++++++++++++++ 2 files changed, 26 insertions(+), 10 deletions(-) diff --git a/block/bio.c b/block/bio.c index 471d738..a1e0b00 100644 --- a/block/bio.c +++ b/block/bio.c @@ -2031,7 +2031,6 @@ 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; @@ -2040,17 +2039,9 @@ int bio_associate_current(struct bio *bio) 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; } diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index b9cb94c..e7da0aa 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -774,6 +774,31 @@ 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 -- 2.1.0 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org