Skip to content

Commit

Permalink
cgroup: separate out taskset operations from cgroup_migrate()
Browse files Browse the repository at this point in the history 
Currently, cgroup_migreate() implements large part of the migration
logic inline including building the target taskset and actually
migrating them.  This patch separates out the following taskset
operations.

 CGROUP_TASKSET_INIT()		: taskset initializer
 cgroup_taskset_add()		: add a task to a taskset
 cgroup_taskset_migrate()	: migrate a taskset to the destination cgroup

This will be used to implement atomic multi-process migration in
cgroup_update_dfl_csses().  This is pure reorganization which doesn't
introduce any functional changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Zefan Li <lizefan@huawei.com>
  • Loading branch information
Tejun Heo committed Sep 22, 2015
1 parent 9af2ec4 commit adaae5d
Showing 1 changed file with 125 additions and 86 deletions.
211 changes: 125 additions & 86 deletions kernel/cgroup.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2144,6 +2144,49 @@ struct cgroup_taskset {
struct task_struct *cur_task;
};

#define CGROUP_TASKSET_INIT(tset) (struct cgroup_taskset){ \
.src_csets = LIST_HEAD_INIT(tset.src_csets), \
.dst_csets = LIST_HEAD_INIT(tset.dst_csets), \
.csets = &tset.src_csets, \
}

/**
* cgroup_taskset_add - try to add a migration target task to a taskset
* @task: target task
* @tset: target taskset
*
* Add @task, which is a migration target, to @tset. This function becomes
* noop if @task doesn't need to be migrated. @task's css_set should have
* been added as a migration source and @task->cg_list will be moved from
* the css_set's tasks list to mg_tasks one.
*/
static void cgroup_taskset_add(struct task_struct *task,
struct cgroup_taskset *tset)
{
struct css_set *cset;

lockdep_assert_held(&css_set_rwsem);

/* @task either already exited or can't exit until the end */
if (task->flags & PF_EXITING)
return;

/* leave @task alone if post_fork() hasn't linked it yet */
if (list_empty(&task->cg_list))
return;

cset = task_css_set(task);
if (!cset->mg_src_cgrp)
return;

list_move_tail(&task->cg_list, &cset->mg_tasks);
if (list_empty(&cset->mg_node))
list_add_tail(&cset->mg_node, &tset->src_csets);
if (list_empty(&cset->mg_dst_cset->mg_node))
list_move_tail(&cset->mg_dst_cset->mg_node,
&tset->dst_csets);
}

/**
* cgroup_taskset_first - reset taskset and return the first task
* @tset: taskset of interest
Expand Down Expand Up @@ -2227,6 +2270,84 @@ static void cgroup_task_migrate(struct cgroup *old_cgrp,
put_css_set_locked(old_cset);
}

/**
* cgroup_taskset_migrate - migrate a taskset to a cgroup
* @tset: taget taskset
* @dst_cgrp: destination cgroup
*
* Migrate tasks in @tset to @dst_cgrp. This function fails iff one of the
* ->can_attach callbacks fails and guarantees that either all or none of
* the tasks in @tset are migrated. @tset is consumed regardless of
* success.
*/
static int cgroup_taskset_migrate(struct cgroup_taskset *tset,
struct cgroup *dst_cgrp)
{
struct cgroup_subsys_state *css, *failed_css = NULL;
struct task_struct *task, *tmp_task;
struct css_set *cset, *tmp_cset;
int i, ret;

/* methods shouldn't be called if no task is actually migrating */
if (list_empty(&tset->src_csets))
return 0;

/* check that we can legitimately attach to the cgroup */
for_each_e_css(css, i, dst_cgrp) {
if (css->ss->can_attach) {
ret = css->ss->can_attach(css, tset);
if (ret) {
failed_css = css;
goto out_cancel_attach;
}
}
}

/*
* Now that we're guaranteed success, proceed to move all tasks to
* the new cgroup. There are no failure cases after here, so this
* is the commit point.
*/
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(cset->mg_src_cgrp, task,
cset->mg_dst_cset);
}
up_write(&css_set_rwsem);

/*
* Migration is committed, all target tasks are now on dst_csets.
* Nothing is sensitive to fork() after this point. Notify
* controllers that migration is complete.
*/
tset->csets = &tset->dst_csets;

for_each_e_css(css, i, dst_cgrp)
if (css->ss->attach)
css->ss->attach(css, tset);

ret = 0;
goto out_release_tset;

out_cancel_attach:
for_each_e_css(css, i, dst_cgrp) {
if (css == failed_css)
break;
if (css->ss->cancel_attach)
css->ss->cancel_attach(css, tset);
}
out_release_tset:
down_write(&css_set_rwsem);
list_splice_init(&tset->dst_csets, &tset->src_csets);
list_for_each_entry_safe(cset, tmp_cset, &tset->src_csets, mg_node) {
list_splice_tail_init(&cset->mg_tasks, &cset->tasks);
list_del_init(&cset->mg_node);
}
up_write(&css_set_rwsem);
return ret;
}

/**
* cgroup_migrate_finish - cleanup after attach
* @preloaded_csets: list of preloaded css_sets
Expand Down Expand Up @@ -2381,15 +2502,8 @@ static int cgroup_migrate_prepare_dst(struct cgroup *dst_cgrp,
static int cgroup_migrate(struct task_struct *leader, bool threadgroup,
struct cgroup *cgrp)
{
struct cgroup_taskset tset = {
.src_csets = LIST_HEAD_INIT(tset.src_csets),
.dst_csets = LIST_HEAD_INIT(tset.dst_csets),
.csets = &tset.src_csets,
};
struct cgroup_subsys_state *css, *failed_css = NULL;
struct css_set *cset, *tmp_cset;
struct task_struct *task, *tmp_task;
int i, ret;
struct cgroup_taskset tset = CGROUP_TASKSET_INIT(tset);
struct task_struct *task;

/*
* Prevent freeing of tasks while we take a snapshot. Tasks that are
Expand All @@ -2400,89 +2514,14 @@ static int cgroup_migrate(struct task_struct *leader, bool threadgroup,
rcu_read_lock();
task = leader;
do {
/* @task either already exited or can't exit until the end */
if (task->flags & PF_EXITING)
goto next;

/* leave @task alone if post_fork() hasn't linked it yet */
if (list_empty(&task->cg_list))
goto next;

cset = task_css_set(task);
if (!cset->mg_src_cgrp)
goto next;

list_move_tail(&task->cg_list, &cset->mg_tasks);
if (list_empty(&cset->mg_node))
list_add_tail(&cset->mg_node, &tset.src_csets);
if (list_empty(&cset->mg_dst_cset->mg_node))
list_move_tail(&cset->mg_dst_cset->mg_node,
&tset.dst_csets);
next:
cgroup_taskset_add(task, &tset);
if (!threadgroup)
break;
} while_each_thread(leader, task);
rcu_read_unlock();
up_write(&css_set_rwsem);

/* methods shouldn't be called if no task is actually migrating */
if (list_empty(&tset.src_csets))
return 0;

/* check that we can legitimately attach to the cgroup */
for_each_e_css(css, i, cgrp) {
if (css->ss->can_attach) {
ret = css->ss->can_attach(css, &tset);
if (ret) {
failed_css = css;
goto out_cancel_attach;
}
}
}

/*
* Now that we're guaranteed success, proceed to move all tasks to
* the new cgroup. There are no failure cases after here, so this
* is the commit point.
*/
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(cset->mg_src_cgrp, task,
cset->mg_dst_cset);
}
up_write(&css_set_rwsem);

/*
* Migration is committed, all target tasks are now on dst_csets.
* Nothing is sensitive to fork() after this point. Notify
* controllers that migration is complete.
*/
tset.csets = &tset.dst_csets;

for_each_e_css(css, i, cgrp)
if (css->ss->attach)
css->ss->attach(css, &tset);

ret = 0;
goto out_release_tset;

out_cancel_attach:
for_each_e_css(css, i, cgrp) {
if (css == failed_css)
break;
if (css->ss->cancel_attach)
css->ss->cancel_attach(css, &tset);
}
out_release_tset:
down_write(&css_set_rwsem);
list_splice_init(&tset.dst_csets, &tset.src_csets);
list_for_each_entry_safe(cset, tmp_cset, &tset.src_csets, mg_node) {
list_splice_tail_init(&cset->mg_tasks, &cset->tasks);
list_del_init(&cset->mg_node);
}
up_write(&css_set_rwsem);
return ret;
return cgroup_taskset_migrate(&tset, cgrp);
}

/**
Expand Down

0 comments on commit adaae5d

Please sign in to comment.