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authorTejun Heo <tj@kernel.org>2013-08-13 20:22:50 -0400
committerTejun Heo <tj@kernel.org>2013-08-13 20:22:50 -0400
commit09a503ea3a816b285b0b402b7f785eaec0c7a7e1 (patch)
tree67f3a360c2e8e0851825cf3e1675bd5244d15926 /kernel/cgroup.c
parentf20104de55a212a9742d8df1807f1f29dc95b748 (diff)
cgroup: decouple cgroup_subsys_state destruction from cgroup destruction
Currently, css (cgroup_subsys_state) lifetime is tied to that of the associated cgroup. css's are created when the associated cgroup is created and destroyed when it gets destroyed. Also, individual css's aren't RCU protected but the whole cgroup is. With the planned unified hierarchy, css's will need to be dynamically created and destroyed within the lifetime of a cgroup. To enable such usages, this patch decouples css destruction from cgroup destruction - offline_css() invocation and the final css_put() are moved from cgroup_destroy_css_killed() to css_killed_work_fn(). Now each css is individually offlined and put as its reference count is killed instead of waiting for all css's attached to the cgroup to finish refcnt killing and then proceeding to offlining and putting them together. While this changes the order of destruction operations, the changes shouldn't be noticeable to cgroup subsystems or userland. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Diffstat (limited to 'kernel/cgroup.c')
-rw-r--r--kernel/cgroup.c52
1 files changed, 24 insertions, 28 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 174f4c3d72e..3c4c4b01ffe 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4355,6 +4355,7 @@ static void offline_css(struct cgroup_subsys_state *css)
ss->css_offline(css);
css->flags &= ~CSS_ONLINE;
+ css->cgroup->nr_css--;
}
/*
@@ -4559,14 +4560,29 @@ static void css_killed_work_fn(struct work_struct *work)
mutex_lock(&cgroup_mutex);
/*
+ * css_tryget() is guaranteed to fail now. Tell subsystems to
+ * initate destruction.
+ */
+ offline_css(css);
+
+ /*
* If @cgrp is marked dead, it's waiting for refs of all css's to
* be disabled before proceeding to the second phase of cgroup
* destruction. If we are the last one, kick it off.
*/
- if (!--cgrp->nr_css && cgroup_is_dead(cgrp))
+ if (!cgrp->nr_css && cgroup_is_dead(cgrp))
cgroup_destroy_css_killed(cgrp);
mutex_unlock(&cgroup_mutex);
+
+ /*
+ * Put the css refs from kill_css(). Each css holds an extra
+ * reference to the cgroup's dentry and cgroup removal proceeds
+ * regardless of css refs. On the last put of each css, whenever
+ * that may be, the extra dentry ref is put so that dentry
+ * destruction happens only after all css's are released.
+ */
+ css_put(css);
}
/* css kill confirmation processing requires process context, bounce */
@@ -4633,11 +4649,10 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
* as killed on all CPUs on return.
*
* Use percpu_ref_kill_and_confirm() to get notifications as each
- * css is confirmed to be seen as killed on all CPUs. The
- * notification callback keeps track of the number of css's to be
- * killed and invokes cgroup_destroy_css_killed() to perform the
- * rest of destruction once the percpu refs of all css's are
- * confirmed to be killed.
+ * css is confirmed to be seen as killed on all CPUs.
+ * cgroup_destroy_css_killed() will be invoked to perform the rest
+ * of destruction once the percpu refs of all css's are confirmed
+ * to be killed.
*/
for_each_root_subsys(cgrp->root, ss) {
struct cgroup_subsys_state *css = cgroup_css(cgrp, ss->subsys_id);
@@ -4704,36 +4719,17 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
* @work: cgroup->destroy_free_work
*
* This function is invoked from a work item for a cgroup which is being
- * destroyed after the percpu refcnts of all css's are guaranteed to be
- * seen as killed on all CPUs, and performs the rest of destruction. This
- * is the second step of destruction described in the comment above
- * cgroup_destroy_locked().
+ * destroyed after all css's are offlined and performs the rest of
+ * destruction. This is the second step of destruction described in the
+ * comment above cgroup_destroy_locked().
*/
static void cgroup_destroy_css_killed(struct cgroup *cgrp)
{
struct cgroup *parent = cgrp->parent;
struct dentry *d = cgrp->dentry;
- struct cgroup_subsys *ss;
lockdep_assert_held(&cgroup_mutex);
- /*
- * css_tryget() is guaranteed to fail now. Tell subsystems to
- * initate destruction.
- */
- for_each_root_subsys(cgrp->root, ss)
- offline_css(cgroup_css(cgrp, ss->subsys_id));
-
- /*
- * Put the css refs from cgroup_destroy_locked(). Each css holds
- * an extra reference to the cgroup's dentry and cgroup removal
- * proceeds regardless of css refs. On the last put of each css,
- * whenever that may be, the extra dentry ref is put so that dentry
- * destruction happens only after all css's are released.
- */
- for_each_root_subsys(cgrp->root, ss)
- css_put(cgroup_css(cgrp, ss->subsys_id));
-
/* delete this cgroup from parent->children */
list_del_rcu(&cgrp->sibling);