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Commit 0f0a2b4f authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: reorganize css_task_iter 



This patch reorganizes css_task_iter so that adding effective css
support is easier.

* s/->cset_link/->cset_pos/ and s/->task/->task_pos/ for consistency

* ->origin_css is used to determine whether the iteration reached the
  last css_set.  Replace it with explicit ->cset_head so that
  css_advance_task_iter() doesn't have to know the termination
  condition directly.

* css_task_iter_next() currently assumes that it's walking list of
  cgrp_cset_link and reaches into the current cset through the current
  link to determine the termination conditions for task walking.  As
  this won't always be true for effective css walking, add
  ->tasks_head and ->mg_tasks_head and use them to control task
  walking so that css_task_iter_next() doesn't have to know how
  css_sets are being walked.

This patch doesn't make any behavior changes.  The iteration logic
stays unchanged after the patch.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent 3b281afb

include/linux/cgroup.h

+6 −3
Original line number Diff line number Diff line
@@ -842,9 +842,12 @@ css_next_descendant_post(struct cgroup_subsys_state *pos, 


/* A css_task_iter should be treated as an opaque object */

struct css_task_iter {

	struct cgroup_subsys_state	*origin_css;

	struct list_head		*cset_link;

	struct list_head		*task;

	struct list_head		*cset_pos;

	struct list_head		*cset_head;



	struct list_head		*task_pos;

	struct list_head		*tasks_head;

	struct list_head		*mg_tasks_head;

};



void css_task_iter_start(struct cgroup_subsys_state *css,

kernel/cgroup.c

+17 −16
Original line number Diff line number Diff line
@@ -2857,27 +2857,30 @@ css_next_descendant_post(struct cgroup_subsys_state *pos, 
 */

static void css_advance_task_iter(struct css_task_iter *it)

{

	struct list_head *l = it->cset_link;

	struct list_head *l = it->cset_pos;

	struct cgrp_cset_link *link;

	struct css_set *cset;



	/* Advance to the next non-empty css_set */

	do {

		l = l->next;

		if (l == &it->origin_css->cgroup->cset_links) {

			it->cset_link = NULL;

		if (l == it->cset_head) {

			it->cset_pos = NULL;

			return;

		}

		link = list_entry(l, struct cgrp_cset_link, cset_link);

		cset = link->cset;

	} while (list_empty(&cset->tasks) && list_empty(&cset->mg_tasks));



	it->cset_link = l;

	it->cset_pos = l;



	if (!list_empty(&cset->tasks))

		it->task = cset->tasks.next;

		it->task_pos = cset->tasks.next;

	else

		it->task = cset->mg_tasks.next;

		it->task_pos = cset->mg_tasks.next;



	it->tasks_head = &cset->tasks;

	it->mg_tasks_head = &cset->mg_tasks;

}



/**
@@ -2903,8 +2906,8 @@ void css_task_iter_start(struct cgroup_subsys_state *css, 


	down_read(&css_set_rwsem);



	it->origin_css = css;

	it->cset_link = &css->cgroup->cset_links;

	it->cset_pos = &css->cgroup->cset_links;

	it->cset_head = it->cset_pos;



	css_advance_task_iter(it);

}
@@ -2920,12 +2923,10 @@ void css_task_iter_start(struct cgroup_subsys_state *css, 
struct task_struct *css_task_iter_next(struct css_task_iter *it)

{

	struct task_struct *res;

	struct list_head *l = it->task;

	struct cgrp_cset_link *link = list_entry(it->cset_link,

					struct cgrp_cset_link, cset_link);

	struct list_head *l = it->task_pos;



	/* If the iterator cg is NULL, we have no tasks */

	if (!it->cset_link)

	if (!it->cset_pos)

		return NULL;

	res = list_entry(l, struct task_struct, cg_list);
@@ -2936,13 +2937,13 @@ struct task_struct *css_task_iter_next(struct css_task_iter *it) 
	 */

	l = l->next;



	if (l == &link->cset->tasks)

		l = link->cset->mg_tasks.next;

	if (l == it->tasks_head)

		l = it->mg_tasks_head->next;



	if (l == &link->cset->mg_tasks)

	if (l == it->mg_tasks_head)

		css_advance_task_iter(it);

	else

		it->task = l;

		it->task_pos = l;



	return res;

}