From adaae5dcf8920375a2fdc6268f762a0b7b331c55 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 11 Sep 2015 15:00:21 -0400 Subject: [PATCH] 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 Acked-by: Zefan Li --- kernel/cgroup.c | 211 ++++++++++++++++++++++++++++-------------------- 1 file changed, 125 insertions(+), 86 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index dc079560dd53..f24d3cedd809 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -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 @@ -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 @@ -2381,15 +2502,8 @@ err: 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 @@ -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); } /** -- 2.20.1