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Date: Fri, 9 Oct 2015 23:29:36 -0400
From: Tejun Heo <tj@...nel.org>
To: lizefan@...wei.com, hannes@...xchg.org
Cc: cgroups@...r.kernel.org, cyphar@...har.com,
linux-kernel@...r.kernel.org, kernel-team@...com,
Tejun Heo <tj@...nel.org>
Subject: [PATCH 09/14] 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@...nel.org>
---
kernel/cgroup.c | 104 ++++++++++++++++++++++++++++++--------------------------
1 file changed, 56 insertions(+), 48 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 5cb28d2..4e239e4 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -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
@@ -2260,47 +2306,6 @@ struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset)
}
/**
- * 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
* @dst_cgrp: destination cgroup
@@ -2340,8 +2345,14 @@ 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);
@@ -5476,9 +5487,8 @@ 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);
}
@@ -5526,9 +5536,7 @@ 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;
}
--
2.4.3
--
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