The reference count in the css_set data structure was used as a
proxy of the number of tasks attached to that css_set. However, that
count is actually not an accurate measure especially with thread mode
support. So a new variable nr_tasks is added to the css_set to keep
track of the actual task count. This new variable is protected by
the css_set_lock. Functions that require the actual task count are
updated to use the new variable.
tj: s/task_count/nr_tasks/ for consistency with cgroup_root->nr_cgrps.
Refreshed on top of cgroup/for-v4.13 which dropped on
css_set_populated() -> nr_tasks conversion.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
/* the default cgroup associated with this css_set */
struct cgroup *dfl_cgrp;
/* the default cgroup associated with this css_set */
struct cgroup *dfl_cgrp;
+ /* internal task count, protected by css_set_lock */
+ int nr_tasks;
+
/*
* Lists running through all tasks using this cgroup group.
* mg_tasks lists tasks which belong to this cset but are in the
/*
* Lists running through all tasks using this cgroup group.
* mg_tasks lists tasks which belong to this cset but are in the
/**
* cgroup_task_count - count the number of tasks in a cgroup.
* @cgrp: the cgroup in question
/**
* cgroup_task_count - count the number of tasks in a cgroup.
* @cgrp: the cgroup in question
- *
- * Return the number of tasks in the cgroup. The returned number can be
- * higher than the actual number of tasks due to css_set references from
- * namespace roots and temporary usages.
*/
static int cgroup_task_count(const struct cgroup *cgrp)
{
*/
static int cgroup_task_count(const struct cgroup *cgrp)
{
spin_lock_irq(&css_set_lock);
list_for_each_entry(link, &cgrp->cset_links, cset_link)
spin_lock_irq(&css_set_lock);
list_for_each_entry(link, &cgrp->cset_links, cset_link)
- count += refcount_read(&link->cset->refcount);
+ count += link->cset->nr_tasks;
spin_unlock_irq(&css_set_lock);
return count;
}
spin_unlock_irq(&css_set_lock);
return count;
}
/**
* css_set_populated - does a css_set contain any tasks?
* @cset: target css_set
/**
* css_set_populated - does a css_set contain any tasks?
* @cset: target css_set
+ *
+ * css_set_populated() should be the same as !!cset->nr_tasks at steady
+ * state. However, css_set_populated() can be called while a task is being
+ * added to or removed from the linked list before the nr_tasks is
+ * properly updated. Hence, we can't just look at ->nr_tasks here.
*/
static bool css_set_populated(struct css_set *cset)
{
*/
static bool css_set_populated(struct css_set *cset)
{
css_set_update_populated(cset, true);
list_add_tail(&p->cg_list, &cset->tasks);
get_css_set(cset);
css_set_update_populated(cset, true);
list_add_tail(&p->cg_list, &cset->tasks);
get_css_set(cset);
}
spin_unlock(&p->sighand->siglock);
} while_each_thread(g, p);
}
spin_unlock(&p->sighand->siglock);
} while_each_thread(g, p);
struct css_set *to_cset = cset->mg_dst_cset;
get_css_set(to_cset);
struct css_set *to_cset = cset->mg_dst_cset;
get_css_set(to_cset);
css_set_move_task(task, from_cset, to_cset, true);
put_css_set_locked(from_cset);
css_set_move_task(task, from_cset, to_cset, true);
put_css_set_locked(from_cset);
}
}
spin_unlock_irq(&css_set_lock);
}
}
spin_unlock_irq(&css_set_lock);
cset = task_css_set(current);
if (list_empty(&child->cg_list)) {
get_css_set(cset);
cset = task_css_set(current);
if (list_empty(&child->cg_list)) {
get_css_set(cset);
css_set_move_task(child, NULL, cset, false);
}
spin_unlock_irq(&css_set_lock);
css_set_move_task(child, NULL, cset, false);
}
spin_unlock_irq(&css_set_lock);
if (!list_empty(&tsk->cg_list)) {
spin_lock_irq(&css_set_lock);
css_set_move_task(tsk, cset, NULL, false);
if (!list_empty(&tsk->cg_list)) {
spin_lock_irq(&css_set_lock);
css_set_move_task(tsk, cset, NULL, false);
spin_unlock_irq(&css_set_lock);
} else {
get_css_set(cset);
spin_unlock_irq(&css_set_lock);
} else {
get_css_set(cset);