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| author | Tejun Heo | 2014-05-08 03:31:17 +0200 |
|---|---|---|
| committer | Tejun Heo | 2014-05-13 17:26:27 +0200 |
| commit | 5024ae29cd285ce9e736776414da645d3a91828c (patch) | |
| tree | 0afef891029af86947869d25b8a3c0e10b6ead69 /include/linux | |
| parent | blkcg: use trylock on blkcg_pol_mutex in blkcg_reset_stats() (diff) | |
| download | kernel-qcow2-linux-5024ae29cd285ce9e736776414da645d3a91828c.tar.gz kernel-qcow2-linux-5024ae29cd285ce9e736776414da645d3a91828c.tar.xz kernel-qcow2-linux-5024ae29cd285ce9e736776414da645d3a91828c.zip | |
cgroup: introduce task_css_is_root()
Determining the css of a task usually requires RCU read lock as that's
the only thing which keeps the returned css accessible till its
reference is acquired; however, testing whether a task belongs to the
root can be performed without dereferencing the returned css by
comparing the returned pointer against the root one in init_css_set[]
which never changes.
Implement task_css_is_root() which can be invoked in any context.
This will be used by the scheduled cgroup_freezer change.
v2: cgroup no longer supports modular controllers. No need to export
init_css_set. Pointed out by Li.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/cgroup.h | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index c2515851c1aa..d60904b9e505 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -473,6 +473,7 @@ struct cftype { }; extern struct cgroup_root cgrp_dfl_root; +extern struct css_set init_css_set; static inline bool cgroup_on_dfl(const struct cgroup *cgrp) { @@ -700,6 +701,20 @@ static inline struct cgroup_subsys_state *task_css(struct task_struct *task, return task_css_check(task, subsys_id, false); } +/** + * task_css_is_root - test whether a task belongs to the root css + * @task: the target task + * @subsys_id: the target subsystem ID + * + * Test whether @task belongs to the root css on the specified subsystem. + * May be invoked in any context. + */ +static inline bool task_css_is_root(struct task_struct *task, int subsys_id) +{ + return task_css_check(task, subsys_id, true) == + init_css_set.subsys[subsys_id]; +} + static inline struct cgroup *task_cgroup(struct task_struct *task, int subsys_id) { |