differences. This will also ease further changes.
-v2: nr_todo renamed to nr_migrating_tasks as per Paul Menage's
suggestion.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Paul Menage <paul@paulmenage.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
---
kernel/cgroup.c | 70 ++++++++++++++++++++++++++++++++++--------------------
1 files changed, 44 insertions(+), 26 deletions(-)
@@ -1739,6 +1739,11 @@ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
}
EXPORT_SYMBOL_GPL(cgroup_path);
+struct task_and_cgroup {
+ struct task_struct *task;
+ struct cgroup *cgrp;
+};
+
/*
* cgroup_task_migrate - move a task from one cgroup to another.
*
@@ -1990,15 +1995,15 @@ static int css_set_prefetch(struct cgroup *cgrp, struct css_set *cg,
*/
int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
{
- int retval, i, group_size;
+ int retval, i, group_size, nr_migrating_tasks;
struct cgroup_subsys *ss, *failed_ss = NULL;
bool cancel_failed_ss = false;
/* guaranteed to be initialized later, but the compiler needs this */
- struct cgroup *oldcgrp = NULL;
struct css_set *oldcg;
struct cgroupfs_root *root = cgrp->root;
/* threadgroup list cursor and array */
struct task_struct *tsk;
+ struct task_and_cgroup *tc;
struct flex_array *group;
/*
* we need to make sure we have css_sets for all the tasks we're
@@ -2017,8 +2022,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
*/
group_size = get_nr_threads(leader);
/* flex_array supports very large thread-groups better than kmalloc. */
- group = flex_array_alloc(sizeof(struct task_struct *), group_size,
- GFP_KERNEL);
+ group = flex_array_alloc(sizeof(*tc), group_size, GFP_KERNEL);
if (!group)
return -ENOMEM;
/* pre-allocate to guarantee space while iterating in rcu read-side. */
@@ -2042,8 +2046,10 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
}
/* take a reference on each task in the group to go in the array. */
tsk = leader;
- i = 0;
+ i = nr_migrating_tasks = 0;
do {
+ struct task_and_cgroup ent;
+
/* as per above, nr_threads may decrease, but not increase. */
BUG_ON(i >= group_size);
get_task_struct(tsk);
@@ -2051,14 +2057,23 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
* saying GFP_ATOMIC has no effect here because we did prealloc
* earlier, but it's good form to communicate our expectations.
*/
- retval = flex_array_put_ptr(group, i, tsk, GFP_ATOMIC);
+ ent.task = tsk;
+ ent.cgrp = task_cgroup_from_root(tsk, root);
+ retval = flex_array_put(group, i, &ent, GFP_ATOMIC);
BUG_ON(retval != 0);
i++;
+ if (ent.cgrp != cgrp)
+ nr_migrating_tasks++;
} while_each_thread(leader, tsk);
/* remember the number of threads in the array for later. */
group_size = i;
rcu_read_unlock();
+ /* methods shouldn't be called if no task is actually migrating */
+ retval = 0;
+ if (!nr_migrating_tasks)
+ goto out_put_tasks;
+
/*
* step 1: check that we can legitimately attach to the cgroup.
*/
@@ -2074,8 +2089,10 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
if (ss->can_attach_task) {
/* run on each task in the threadgroup. */
for (i = 0; i < group_size; i++) {
- tsk = flex_array_get_ptr(group, i);
- retval = ss->can_attach_task(cgrp, tsk);
+ tc = flex_array_get(group, i);
+ if (tc->cgrp == cgrp)
+ continue;
+ retval = ss->can_attach_task(cgrp, tc->task);
if (retval) {
failed_ss = ss;
cancel_failed_ss = true;
@@ -2091,23 +2108,22 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
*/
INIT_LIST_HEAD(&newcg_list);
for (i = 0; i < group_size; i++) {
- tsk = flex_array_get_ptr(group, i);
+ tc = flex_array_get(group, i);
/* nothing to do if this task is already in the cgroup */
- oldcgrp = task_cgroup_from_root(tsk, root);
- if (cgrp == oldcgrp)
+ if (tc->cgrp == cgrp)
continue;
/* get old css_set pointer */
- task_lock(tsk);
- if (tsk->flags & PF_EXITING) {
+ task_lock(tc->task);
+ if (tc->task->flags & PF_EXITING) {
/* ignore this task if it's going away */
- task_unlock(tsk);
+ task_unlock(tc->task);
continue;
}
- oldcg = tsk->cgroups;
+ oldcg = tc->task->cgroups;
get_css_set(oldcg);
- task_unlock(tsk);
+ task_unlock(tc->task);
/* see if the new one for us is already in the list? */
- if (css_set_check_fetched(cgrp, tsk, oldcg, &newcg_list)) {
+ if (css_set_check_fetched(cgrp, tc->task, oldcg, &newcg_list)) {
/* was already there, nothing to do. */
put_css_set(oldcg);
} else {
@@ -2130,20 +2146,19 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
ss->pre_attach(cgrp);
}
for (i = 0; i < group_size; i++) {
- tsk = flex_array_get_ptr(group, i);
+ tc = flex_array_get(group, i);
/* leave current thread as it is if it's already there */
- oldcgrp = task_cgroup_from_root(tsk, root);
- if (cgrp == oldcgrp)
+ if (tc->cgrp == cgrp)
continue;
/* if the thread is PF_EXITING, it can just get skipped. */
- retval = cgroup_task_migrate(cgrp, oldcgrp, tsk, true);
+ retval = cgroup_task_migrate(cgrp, tc->cgrp, tc->task, true);
BUG_ON(retval != 0 && retval != -ESRCH);
/* attach each task to each subsystem */
for_each_subsys(root, ss) {
if (ss->attach_task)
- ss->attach_task(cgrp, tsk);
+ ss->attach_task(cgrp, tc->task);
}
}
/* nothing is sensitive to fork() after this point. */
@@ -2154,8 +2169,10 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
* being moved, this call will need to be reworked to communicate that.
*/
for_each_subsys(root, ss) {
- if (ss->attach)
- ss->attach(ss, cgrp, oldcgrp, leader);
+ if (ss->attach) {
+ tc = flex_array_get(group, 0);
+ ss->attach(ss, cgrp, tc->cgrp, tc->task);
+ }
}
/*
@@ -2184,10 +2201,11 @@ out_cancel_attach:
ss->cancel_attach(ss, cgrp, leader);
}
}
+out_put_tasks:
/* clean up the array of referenced threads in the group. */
for (i = 0; i < group_size; i++) {
- tsk = flex_array_get_ptr(group, i);
- put_task_struct(tsk);
+ tc = flex_array_get(group, i);
+ put_task_struct(tc->task);
}
out_free_group_list:
flex_array_free(group);