From 73a7242a06ff995d771fbe243e72b516feaa6e3d Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Tue, 13 Jun 2017 17:18:01 -0400 Subject: cgroup: Keep accurate count of tasks in each css_set 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 Signed-off-by: Tejun Heo --- kernel/cgroup/cgroup.c | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'kernel/cgroup/cgroup.c') diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 8d4e85eae42c..dbfd7028b1c6 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -573,6 +573,11 @@ static int css_set_count = 1; /* 1 for init_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) { @@ -1598,6 +1603,7 @@ static void cgroup_enable_task_cg_lists(void) css_set_update_populated(cset, true); list_add_tail(&p->cg_list, &cset->tasks); get_css_set(cset); + cset->nr_tasks++; } spin_unlock(&p->sighand->siglock); } while_each_thread(g, p); @@ -2064,8 +2070,10 @@ static int cgroup_migrate_execute(struct cgroup_mgctx *mgctx) struct css_set *to_cset = cset->mg_dst_cset; get_css_set(to_cset); + to_cset->nr_tasks++; css_set_move_task(task, from_cset, to_cset, true); put_css_set_locked(from_cset); + from_cset->nr_tasks--; } } spin_unlock_irq(&css_set_lock); @@ -4789,6 +4797,7 @@ void cgroup_post_fork(struct task_struct *child) cset = task_css_set(current); if (list_empty(&child->cg_list)) { get_css_set(cset); + cset->nr_tasks++; css_set_move_task(child, NULL, cset, false); } spin_unlock_irq(&css_set_lock); @@ -4838,6 +4847,7 @@ void cgroup_exit(struct task_struct *tsk) if (!list_empty(&tsk->cg_list)) { spin_lock_irq(&css_set_lock); css_set_move_task(tsk, cset, NULL, false); + cset->nr_tasks--; spin_unlock_irq(&css_set_lock); } else { get_css_set(cset); -- cgit