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authorTejun Heo <tj@kernel.org>2014-05-07 21:31:17 -0400
committerTejun Heo <tj@kernel.org>2014-05-13 11:26:27 -0400
commit5024ae29cd285ce9e736776414da645d3a91828c (patch)
tree0afef891029af86947869d25b8a3c0e10b6ead69 /include/linux/cgroup.h
parent36c38fb7144aa941dc072ba8f58b2dbe509c0345 (diff)
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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/cgroup.h')
-rw-r--r--include/linux/cgroup.h15
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)
{