From ec438699a9ae0856c2ce20a50dd39cdc7e92a732 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 22 May 2015 17:13:22 -0400 Subject: cgroup, block: implement task_get_css() and use it in bio_associate_current() 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 Signed-off-by: Jens Axboe --- include/linux/cgroup.h | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) (limited to 'include/linux/cgroup.h') diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index b9cb94c3102a..e7da0aa65b2d 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -773,6 +773,31 @@ static inline struct cgroup_subsys_state *task_css(struct task_struct *task, return task_css_check(task, subsys_id, false); } +/** + * 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 -- cgit v1.2.3