cgroup: introduce cgroup_taskset and use it in subsys->can_attach(), cancel_attach() and attach()
Currently, there's no way to pass multiple tasks to cgroup_subsys
methods necessitating the need for separate per-process and per-task
methods. This patch introduces cgroup_taskset which can be used to
pass multiple tasks and their associated cgroups to cgroup_subsys
methods.
Three methods - can_attach(), cancel_attach() and attach() - are
converted to use cgroup_taskset. This unifies passed parameters so
that all methods have access to all information. Conversions in this
patchset are identical and don't introduce any behavior change.
-v2: documentation updated as per Paul Menage's suggestion.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Paul Menage <paul@paulmenage.org>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: James Morris <jmorris@namei.org>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 0f2d005..41ee01e 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1757,11 +1757,85 @@
}
EXPORT_SYMBOL_GPL(cgroup_path);
+/*
+ * Control Group taskset
+ */
struct task_and_cgroup {
struct task_struct *task;
struct cgroup *cgrp;
};
+struct cgroup_taskset {
+ struct task_and_cgroup single;
+ struct flex_array *tc_array;
+ int tc_array_len;
+ int idx;
+ struct cgroup *cur_cgrp;
+};
+
+/**
+ * cgroup_taskset_first - reset taskset and return the first task
+ * @tset: taskset of interest
+ *
+ * @tset iteration is initialized and the first task is returned.
+ */
+struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset)
+{
+ if (tset->tc_array) {
+ tset->idx = 0;
+ return cgroup_taskset_next(tset);
+ } else {
+ tset->cur_cgrp = tset->single.cgrp;
+ return tset->single.task;
+ }
+}
+EXPORT_SYMBOL_GPL(cgroup_taskset_first);
+
+/**
+ * cgroup_taskset_next - iterate to the next task in taskset
+ * @tset: taskset of interest
+ *
+ * Return the next task in @tset. Iteration must have been initialized
+ * with cgroup_taskset_first().
+ */
+struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset)
+{
+ struct task_and_cgroup *tc;
+
+ if (!tset->tc_array || tset->idx >= tset->tc_array_len)
+ return NULL;
+
+ tc = flex_array_get(tset->tc_array, tset->idx++);
+ tset->cur_cgrp = tc->cgrp;
+ return tc->task;
+}
+EXPORT_SYMBOL_GPL(cgroup_taskset_next);
+
+/**
+ * cgroup_taskset_cur_cgroup - return the matching cgroup for the current task
+ * @tset: taskset of interest
+ *
+ * Return the cgroup for the current (last returned) task of @tset. This
+ * function must be preceded by either cgroup_taskset_first() or
+ * cgroup_taskset_next().
+ */
+struct cgroup *cgroup_taskset_cur_cgroup(struct cgroup_taskset *tset)
+{
+ return tset->cur_cgrp;
+}
+EXPORT_SYMBOL_GPL(cgroup_taskset_cur_cgroup);
+
+/**
+ * cgroup_taskset_size - return the number of tasks in taskset
+ * @tset: taskset of interest
+ */
+int cgroup_taskset_size(struct cgroup_taskset *tset)
+{
+ return tset->tc_array ? tset->tc_array_len : 1;
+}
+EXPORT_SYMBOL_GPL(cgroup_taskset_size);
+
+
/*
* cgroup_task_migrate - move a task from one cgroup to another.
*
@@ -1842,6 +1916,7 @@
struct cgroup_subsys *ss, *failed_ss = NULL;
struct cgroup *oldcgrp;
struct cgroupfs_root *root = cgrp->root;
+ struct cgroup_taskset tset = { };
/* @tsk either already exited or can't exit until the end */
if (tsk->flags & PF_EXITING)
@@ -1852,9 +1927,12 @@
if (cgrp == oldcgrp)
return 0;
+ tset.single.task = tsk;
+ tset.single.cgrp = oldcgrp;
+
for_each_subsys(root, ss) {
if (ss->can_attach) {
- retval = ss->can_attach(ss, cgrp, tsk);
+ retval = ss->can_attach(ss, cgrp, &tset);
if (retval) {
/*
* Remember on which subsystem the can_attach()
@@ -1885,7 +1963,7 @@
if (ss->attach_task)
ss->attach_task(cgrp, tsk);
if (ss->attach)
- ss->attach(ss, cgrp, oldcgrp, tsk);
+ ss->attach(ss, cgrp, &tset);
}
synchronize_rcu();
@@ -1907,7 +1985,7 @@
*/
break;
if (ss->cancel_attach)
- ss->cancel_attach(ss, cgrp, tsk);
+ ss->cancel_attach(ss, cgrp, &tset);
}
}
return retval;
@@ -2023,6 +2101,7 @@
struct task_struct *tsk;
struct task_and_cgroup *tc;
struct flex_array *group;
+ struct cgroup_taskset tset = { };
/*
* we need to make sure we have css_sets for all the tasks we're
* going to move -before- we actually start moving them, so that in
@@ -2089,6 +2168,8 @@
} while_each_thread(leader, tsk);
/* remember the number of threads in the array for later. */
group_size = i;
+ tset.tc_array = group;
+ tset.tc_array_len = group_size;
read_unlock(&tasklist_lock);
/* methods shouldn't be called if no task is actually migrating */
@@ -2101,7 +2182,7 @@
*/
for_each_subsys(root, ss) {
if (ss->can_attach) {
- retval = ss->can_attach(ss, cgrp, leader);
+ retval = ss->can_attach(ss, cgrp, &tset);
if (retval) {
failed_ss = ss;
goto out_cancel_attach;
@@ -2183,10 +2264,8 @@
* being moved, this call will need to be reworked to communicate that.
*/
for_each_subsys(root, ss) {
- if (ss->attach) {
- tc = flex_array_get(group, 0);
- ss->attach(ss, cgrp, tc->cgrp, tc->task);
- }
+ if (ss->attach)
+ ss->attach(ss, cgrp, &tset);
}
/*
@@ -2208,11 +2287,11 @@
for_each_subsys(root, ss) {
if (ss == failed_ss) {
if (cancel_failed_ss && ss->cancel_attach)
- ss->cancel_attach(ss, cgrp, leader);
+ ss->cancel_attach(ss, cgrp, &tset);
break;
}
if (ss->cancel_attach)
- ss->cancel_attach(ss, cgrp, leader);
+ ss->cancel_attach(ss, cgrp, &tset);
}
}
out_put_tasks:
