cgroup: separate out taskset operations from cgroup_migrate()
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>
This commit is contained in:
Tejun Heo
Родитель
9af2ec45c2
Коммит
adaae5dcf8
211
kernel/cgroup.c
211
kernel/cgroup.c
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@ -2144,6 +2144,49 @@ struct cgroup_taskset {
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struct task_struct *cur_task;
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};
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#define CGROUP_TASKSET_INIT(tset) (struct cgroup_taskset){ \
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.src_csets = LIST_HEAD_INIT(tset.src_csets), \
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.dst_csets = LIST_HEAD_INIT(tset.dst_csets), \
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.csets = &tset.src_csets, \
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}
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/**
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* cgroup_taskset_add - try to add a migration target task to a taskset
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* @task: target task
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* @tset: target taskset
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*
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* Add @task, which is a migration target, to @tset. This function becomes
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* noop if @task doesn't need to be migrated. @task's css_set should have
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* been added as a migration source and @task->cg_list will be moved from
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* the css_set's tasks list to mg_tasks one.
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*/
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static void cgroup_taskset_add(struct task_struct *task,
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struct cgroup_taskset *tset)
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{
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struct css_set *cset;
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lockdep_assert_held(&css_set_rwsem);
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/* @task either already exited or can't exit until the end */
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if (task->flags & PF_EXITING)
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return;
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/* leave @task alone if post_fork() hasn't linked it yet */
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if (list_empty(&task->cg_list))
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return;
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cset = task_css_set(task);
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if (!cset->mg_src_cgrp)
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return;
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list_move_tail(&task->cg_list, &cset->mg_tasks);
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if (list_empty(&cset->mg_node))
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list_add_tail(&cset->mg_node, &tset->src_csets);
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if (list_empty(&cset->mg_dst_cset->mg_node))
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list_move_tail(&cset->mg_dst_cset->mg_node,
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&tset->dst_csets);
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}
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/**
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* cgroup_taskset_first - reset taskset and return the first task
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* @tset: taskset of interest
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@ -2227,6 +2270,84 @@ static void cgroup_task_migrate(struct cgroup *old_cgrp,
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put_css_set_locked(old_cset);
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}
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/**
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* cgroup_taskset_migrate - migrate a taskset to a cgroup
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* @tset: taget taskset
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* @dst_cgrp: destination cgroup
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*
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* Migrate tasks in @tset to @dst_cgrp. This function fails iff one of the
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* ->can_attach callbacks fails and guarantees that either all or none of
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* the tasks in @tset are migrated. @tset is consumed regardless of
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* success.
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*/
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static int cgroup_taskset_migrate(struct cgroup_taskset *tset,
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struct cgroup *dst_cgrp)
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{
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struct cgroup_subsys_state *css, *failed_css = NULL;
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struct task_struct *task, *tmp_task;
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struct css_set *cset, *tmp_cset;
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int i, ret;
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/* methods shouldn't be called if no task is actually migrating */
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if (list_empty(&tset->src_csets))
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return 0;
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/* check that we can legitimately attach to the cgroup */
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for_each_e_css(css, i, dst_cgrp) {
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if (css->ss->can_attach) {
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ret = css->ss->can_attach(css, tset);
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if (ret) {
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failed_css = css;
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goto out_cancel_attach;
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}
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}
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}
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/*
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* Now that we're guaranteed success, proceed to move all tasks to
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* the new cgroup. There are no failure cases after here, so this
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* is the commit point.
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*/
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down_write(&css_set_rwsem);
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list_for_each_entry(cset, &tset->src_csets, mg_node) {
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list_for_each_entry_safe(task, tmp_task, &cset->mg_tasks, cg_list)
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cgroup_task_migrate(cset->mg_src_cgrp, task,
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cset->mg_dst_cset);
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}
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up_write(&css_set_rwsem);
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/*
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* Migration is committed, all target tasks are now on dst_csets.
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* Nothing is sensitive to fork() after this point. Notify
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* controllers that migration is complete.
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*/
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tset->csets = &tset->dst_csets;
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for_each_e_css(css, i, dst_cgrp)
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if (css->ss->attach)
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css->ss->attach(css, tset);
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ret = 0;
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goto out_release_tset;
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out_cancel_attach:
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for_each_e_css(css, i, dst_cgrp) {
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if (css == failed_css)
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break;
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if (css->ss->cancel_attach)
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css->ss->cancel_attach(css, tset);
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}
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out_release_tset:
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down_write(&css_set_rwsem);
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list_splice_init(&tset->dst_csets, &tset->src_csets);
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list_for_each_entry_safe(cset, tmp_cset, &tset->src_csets, mg_node) {
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list_splice_tail_init(&cset->mg_tasks, &cset->tasks);
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list_del_init(&cset->mg_node);
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}
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up_write(&css_set_rwsem);
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return ret;
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}
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/**
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* cgroup_migrate_finish - cleanup after attach
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* @preloaded_csets: list of preloaded css_sets
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@ -2381,15 +2502,8 @@ err:
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static int cgroup_migrate(struct task_struct *leader, bool threadgroup,
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struct cgroup *cgrp)
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{
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struct cgroup_taskset tset = {
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.src_csets = LIST_HEAD_INIT(tset.src_csets),
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.dst_csets = LIST_HEAD_INIT(tset.dst_csets),
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.csets = &tset.src_csets,
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};
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struct cgroup_subsys_state *css, *failed_css = NULL;
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struct css_set *cset, *tmp_cset;
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struct task_struct *task, *tmp_task;
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int i, ret;
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struct cgroup_taskset tset = CGROUP_TASKSET_INIT(tset);
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struct task_struct *task;
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/*
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* Prevent freeing of tasks while we take a snapshot. Tasks that are
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@ -2400,89 +2514,14 @@ static int cgroup_migrate(struct task_struct *leader, bool threadgroup,
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rcu_read_lock();
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task = leader;
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do {
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/* @task either already exited or can't exit until the end */
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if (task->flags & PF_EXITING)
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goto next;
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/* leave @task alone if post_fork() hasn't linked it yet */
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if (list_empty(&task->cg_list))
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goto next;
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cset = task_css_set(task);
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if (!cset->mg_src_cgrp)
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goto next;
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list_move_tail(&task->cg_list, &cset->mg_tasks);
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if (list_empty(&cset->mg_node))
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list_add_tail(&cset->mg_node, &tset.src_csets);
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if (list_empty(&cset->mg_dst_cset->mg_node))
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list_move_tail(&cset->mg_dst_cset->mg_node,
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&tset.dst_csets);
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next:
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cgroup_taskset_add(task, &tset);
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if (!threadgroup)
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break;
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} while_each_thread(leader, task);
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rcu_read_unlock();
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up_write(&css_set_rwsem);
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/* methods shouldn't be called if no task is actually migrating */
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if (list_empty(&tset.src_csets))
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return 0;
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/* check that we can legitimately attach to the cgroup */
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for_each_e_css(css, i, cgrp) {
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if (css->ss->can_attach) {
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ret = css->ss->can_attach(css, &tset);
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if (ret) {
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failed_css = css;
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goto out_cancel_attach;
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}
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}
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}
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/*
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* Now that we're guaranteed success, proceed to move all tasks to
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* the new cgroup. There are no failure cases after here, so this
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* is the commit point.
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*/
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down_write(&css_set_rwsem);
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list_for_each_entry(cset, &tset.src_csets, mg_node) {
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list_for_each_entry_safe(task, tmp_task, &cset->mg_tasks, cg_list)
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cgroup_task_migrate(cset->mg_src_cgrp, task,
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cset->mg_dst_cset);
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}
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up_write(&css_set_rwsem);
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/*
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* Migration is committed, all target tasks are now on dst_csets.
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* Nothing is sensitive to fork() after this point. Notify
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* controllers that migration is complete.
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*/
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tset.csets = &tset.dst_csets;
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for_each_e_css(css, i, cgrp)
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if (css->ss->attach)
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css->ss->attach(css, &tset);
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ret = 0;
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goto out_release_tset;
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out_cancel_attach:
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for_each_e_css(css, i, cgrp) {
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if (css == failed_css)
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break;
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if (css->ss->cancel_attach)
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css->ss->cancel_attach(css, &tset);
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}
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out_release_tset:
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down_write(&css_set_rwsem);
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list_splice_init(&tset.dst_csets, &tset.src_csets);
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list_for_each_entry_safe(cset, tmp_cset, &tset.src_csets, mg_node) {
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list_splice_tail_init(&cset->mg_tasks, &cset->tasks);
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list_del_init(&cset->mg_node);
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}
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up_write(&css_set_rwsem);
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return ret;
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return cgroup_taskset_migrate(&tset, cgrp);
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}
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/**
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