Commit 5024ae29 authored by Tejun Heo's avatar Tejun Heo
Browse files

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: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent 36c38fb7

include/linux/cgroup.h

+15 −0
Original line number Diff line number Diff line
@@ -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)

{

kernel/cgroup.c

+1 −1
Original line number Diff line number Diff line
@@ -348,7 +348,7 @@ struct cgrp_cset_link { 
 * reference-counted, to improve performance when child cgroups

 * haven't been created.

 */

static struct css_set init_css_set = {

struct css_set init_css_set = {

	.refcount		= ATOMIC_INIT(1),

	.cgrp_links		= LIST_HEAD_INIT(init_css_set.cgrp_links),

	.tasks			= LIST_HEAD_INIT(init_css_set.tasks),

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