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cgroup: factor out css_set_move_task() 

A task is associated and disassociated with its css_set in three
places - during migration, after a new task is created and when a task
exits.  The first is handled by cgroup_task_migrate() and the latter
two are open-coded.

These are similar operations and spreading them over multiple places
makes it harder to follow and update.  This patch collects all task
css_set [dis]association operations into css_set_move_task().

While css_set_move_task() may check whether populated state needs to
be updated when not strictly necessary, the behavior is essentially
equivalent before and after this patch.

Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Tejun Heo 2015-10-15 16:41:52 -04:00
parent 389b9c1bc9
commit f6d7d049c1
1 changed files with 56 additions and 48 deletions
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104
kernel/cgroup.c
View File

@ -664,6 +664,52 @@ static void css_set_update_populated(struct css_set *cset, bool populated)
cgroup_update_populated(link->cgrp, populated);
}
/**
* css_set_move_task - move a task from one css_set to another
* @task: task being moved
* @from_cset: css_set @task currently belongs to (may be NULL)
* @to_cset: new css_set @task is being moved to (may be NULL)
* @use_mg_tasks: move to @to_cset->mg_tasks instead of ->tasks
*
* Move @task from @from_cset to @to_cset. If @task didn't belong to any
* css_set, @from_cset can be NULL. If @task is being disassociated
* instead of moved, @to_cset can be NULL.
*
* This function automatically handles populated_cnt updates but the caller
* is responsible for managing @from_cset and @to_cset's reference counts.
*/
static void css_set_move_task(struct task_struct *task,
struct css_set *from_cset, struct css_set *to_cset,
bool use_mg_tasks)
{
lockdep_assert_held(&css_set_rwsem);
if (from_cset) {
WARN_ON_ONCE(list_empty(&task->cg_list));
list_del_init(&task->cg_list);
if (!css_set_populated(from_cset))
css_set_update_populated(from_cset, false);
} else {
WARN_ON_ONCE(!list_empty(&task->cg_list));
}
if (to_cset) {
/*
* We are synchronized through cgroup_threadgroup_rwsem
* against PF_EXITING setting such that we can't race
* against cgroup_exit() changing the css_set to
* init_css_set and dropping the old one.
*/
WARN_ON_ONCE(task->flags & PF_EXITING);
if (!css_set_populated(to_cset))
css_set_update_populated(to_cset, true);
rcu_assign_pointer(task->cgroups, to_cset);
list_add_tail(&task->cg_list, use_mg_tasks ? &to_cset->mg_tasks :
&to_cset->tasks);
}
}
/*
* hash table for cgroup groups. This improves the performance to find
* an existing css_set. This hash doesn't (currently) take into
@ -2261,47 +2307,6 @@ struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset)
return NULL;
}
/**
* cgroup_task_migrate - move a task from one cgroup to another.
* @tsk: the task being migrated
* @new_cset: the new css_set @tsk is being attached to
*
* Must be called with cgroup_mutex, threadgroup and css_set_rwsem locked.
*/
static void cgroup_task_migrate(struct task_struct *tsk,
struct css_set *new_cset)
{
struct css_set *old_cset;
lockdep_assert_held(&cgroup_mutex);
lockdep_assert_held(&css_set_rwsem);
/*
* We are synchronized through cgroup_threadgroup_rwsem against
* PF_EXITING setting such that we can't race against cgroup_exit()
* changing the css_set to init_css_set and dropping the old one.
*/
WARN_ON_ONCE(tsk->flags & PF_EXITING);
old_cset = task_css_set(tsk);
if (!css_set_populated(new_cset))
css_set_update_populated(new_cset, true);
get_css_set(new_cset);
rcu_assign_pointer(tsk->cgroups, new_cset);
list_move_tail(&tsk->cg_list, &new_cset->mg_tasks);
if (!css_set_populated(old_cset))
css_set_update_populated(old_cset, false);
/*
* We just gained a reference on old_cset by taking it from the
* task. As trading it for new_cset is protected by cgroup_mutex,
* we're safe to drop it here; it will be freed under RCU.
*/
put_css_set_locked(old_cset);
}
/**
* cgroup_taskset_migrate - migrate a taskset to a cgroup
* @tset: taget taskset
@ -2342,8 +2347,14 @@ static int cgroup_taskset_migrate(struct cgroup_taskset *tset,
*/
down_write(&css_set_rwsem);
list_for_each_entry(cset, &tset->src_csets, mg_node) {
list_for_each_entry_safe(task, tmp_task, &cset->mg_tasks, cg_list)
cgroup_task_migrate(task, cset->mg_dst_cset);
list_for_each_entry_safe(task, tmp_task, &cset->mg_tasks, cg_list) {
struct css_set *from_cset = task_css_set(task);
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);
}
}
up_write(&css_set_rwsem);
@ -5478,9 +5489,8 @@ void cgroup_post_fork(struct task_struct *child,
down_write(&css_set_rwsem);
cset = task_css_set(current);
if (list_empty(&child->cg_list)) {
rcu_assign_pointer(child->cgroups, cset);
list_add_tail(&child->cg_list, &cset->tasks);
get_css_set(cset);
css_set_move_task(child, NULL, cset, false);
}
up_write(&css_set_rwsem);
}
@ -5528,9 +5538,7 @@ void cgroup_exit(struct task_struct *tsk)
if (!list_empty(&tsk->cg_list)) {
down_write(&css_set_rwsem);
list_del_init(&tsk->cg_list);
if (!css_set_populated(cset))
css_set_update_populated(cset, false);
css_set_move_task(tsk, cset, NULL, false);
up_write(&css_set_rwsem);
put_cset = true;
}