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cgroup: reorder the operations in cgroup_destroy_locked()

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This patch reorders the operations in cgroup_destroy_locked() such
that the userland visible parts happen before css offlining and
removal from the ->sibling list.  This will be used to make css use
percpu refcnt.

While at it, split out CGRP_DEAD related comment from the refcnt
deactivation one and correct / clarify how different guarantees are
met.

While this patch changes the specific order of operations, it
shouldn't cause any noticeable behavior difference.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
This commit is contained in:
Tejun Heo 2013-06-13 19:27:41 -07:00
parent 6f3d828f0f
commit 455050d23e
1 changed files with 35 additions and 26 deletions
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61
kernel/cgroup.c
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@ -4379,13 +4379,8 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
/*
* Block new css_tryget() by deactivating refcnt and mark @cgrp
* removed. This makes future css_tryget() and child creation
* attempts fail thus maintaining the removal conditions verified
* above.
*
* Note that CGRP_DEAD assertion is depended upon by
* cgroup_next_sibling() to resume iteration after dropping RCU
* read lock. See cgroup_next_sibling() for details.
* removed. This makes future css_tryget() attempts fail which we
* guarantee to ->css_offline() callbacks.
*/
for_each_subsys(cgrp->root, ss) {
struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
@ -4393,8 +4388,41 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
WARN_ON(atomic_read(&css->refcnt) < 0);
atomic_add(CSS_DEACT_BIAS, &css->refcnt);
}
/*
* Mark @cgrp dead. This prevents further task migration and child
* creation by disabling cgroup_lock_live_group(). Note that
* CGRP_DEAD assertion is depended upon by cgroup_next_sibling() to
* resume iteration after dropping RCU read lock. See
* cgroup_next_sibling() for details.
*/
set_bit(CGRP_DEAD, &cgrp->flags);
/* CGRP_DEAD is set, remove from ->release_list for the last time */
raw_spin_lock(&release_list_lock);
if (!list_empty(&cgrp->release_list))
list_del_init(&cgrp->release_list);
raw_spin_unlock(&release_list_lock);
/*
* Remove @cgrp directory. The removal puts the base ref but we
* aren't quite done with @cgrp yet, so hold onto it.
*/
dget(d);
cgroup_d_remove_dir(d);
/*
* Unregister events and notify userspace.
* Notify userspace about cgroup removing only after rmdir of cgroup
* directory to avoid race between userspace and kernelspace.
*/
spin_lock(&cgrp->event_list_lock);
list_for_each_entry_safe(event, tmp, &cgrp->event_list, list) {
list_del_init(&event->list);
schedule_work(&event->remove);
}
spin_unlock(&cgrp->event_list_lock);
/* tell subsystems to initate destruction */
for_each_subsys(cgrp->root, ss)
offline_css(ss, cgrp);
@ -4409,34 +4437,15 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
for_each_subsys(cgrp->root, ss)
css_put(cgrp->subsys[ss->subsys_id]);
raw_spin_lock(&release_list_lock);
if (!list_empty(&cgrp->release_list))
list_del_init(&cgrp->release_list);
raw_spin_unlock(&release_list_lock);
/* delete this cgroup from parent->children */
list_del_rcu(&cgrp->sibling);
list_del_init(&cgrp->allcg_node);
dget(d);
cgroup_d_remove_dir(d);
dput(d);
set_bit(CGRP_RELEASABLE, &parent->flags);
check_for_release(parent);
/*
* Unregister events and notify userspace.
* Notify userspace about cgroup removing only after rmdir of cgroup
* directory to avoid race between userspace and kernelspace.
*/
spin_lock(&cgrp->event_list_lock);
list_for_each_entry_safe(event, tmp, &cgrp->event_list, list) {
list_del_init(&event->list);
schedule_work(&event->remove);
}
spin_unlock(&cgrp->event_list_lock);
return 0;
}