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Commit eeecbd19 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: implement cgroup_get_e_css() 



Implement cgroup_get_e_css() which finds and gets the effective css
for the specified cgroup and subsystem combination.  This function
always returns a valid pinned css.  This will be used by cgroup
writeback support.

While at it, add comment to cgroup_e_css() to explain why that
function is different from cgroup_get_e_css() and has to test
cgrp->child_subsys_mask instead of cgroup_css(cgrp, ss).

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarZefan Li <lizefan@huawei.com>
parent 56c807ba

include/linux/cgroup.h

+2 −0
Original line number Diff line number Diff line
@@ -910,6 +910,8 @@ void css_task_iter_end(struct css_task_iter *it); 
int cgroup_attach_task_all(struct task_struct *from, struct task_struct *);

int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from);



struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgroup,

					     struct cgroup_subsys *ss);

struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry,

						       struct cgroup_subsys *ss);

kernel/cgroup.c

+37 −0
Original line number Diff line number Diff line
@@ -277,6 +277,10 @@ static struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp, 
	if (!(cgrp->root->subsys_mask & (1 << ss->id)))

		return NULL;



	/*

	 * This function is used while updating css associations and thus

	 * can't test the csses directly.  Use ->child_subsys_mask.

	 */

	while (cgroup_parent(cgrp) &&

	       !(cgroup_parent(cgrp)->child_subsys_mask & (1 << ss->id)))

		cgrp = cgroup_parent(cgrp);
@@ -284,6 +288,39 @@ static struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp, 
	return cgroup_css(cgrp, ss);

}



/**

 * cgroup_get_e_css - get a cgroup's effective css for the specified subsystem

 * @cgrp: the cgroup of interest

 * @ss: the subsystem of interest

 *

 * Find and get the effective css of @cgrp for @ss.  The effective css is

 * defined as the matching css of the nearest ancestor including self which

 * has @ss enabled.  If @ss is not mounted on the hierarchy @cgrp is on,

 * the root css is returned, so this function always returns a valid css.

 * The returned css must be put using css_put().

 */

struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgrp,

					     struct cgroup_subsys *ss)

{

	struct cgroup_subsys_state *css;



	rcu_read_lock();



	do {

		css = cgroup_css(cgrp, ss);



		if (css && css_tryget_online(css))

			goto out_unlock;

		cgrp = cgroup_parent(cgrp);

	} while (cgrp);



	css = init_css_set.subsys[ss->id];

	css_get(css);

out_unlock:

	rcu_read_unlock();

	return css;

}



/* convenient tests for these bits */

static inline bool cgroup_is_dead(const struct cgroup *cgrp)

{