cgroup_freezer: add ->post_create() and ->pre_destroy() and track online state
A cgroup is online and visible to iteration between ->post_create()
and ->pre_destroy(). This patch introduces CGROUP_FREEZER_ONLINE and
toggles it from the newly added freezer_post_create() and
freezer_pre_destroy() while holding freezer->lock such that a
cgroup_freezer can be reilably distinguished to be online. This will
be used by full hierarchy support.
ONLINE test is added to freezer_apply_state() but it currently doesn't
make any difference as freezer_write() can only be called for an
online cgroup.
Adjusting system_freezing_cnt on destruction is moved from
freezer_destroy() to the new freezer_pre_destroy() for consistency.
This patch doesn't introduce any noticeable behavior change.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index b8ad93c..4f12d31 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -23,6 +23,7 @@
#include <linux/seq_file.h>
enum freezer_state_flags {
+ CGROUP_FREEZER_ONLINE = (1 << 0), /* freezer is fully online */
CGROUP_FREEZING_SELF = (1 << 1), /* this freezer is freezing */
CGROUP_FREEZING_PARENT = (1 << 2), /* the parent freezer is freezing */
CGROUP_FROZEN = (1 << 3), /* this and its descendants frozen */
@@ -98,13 +99,45 @@
return &freezer->css;
}
-static void freezer_destroy(struct cgroup *cgroup)
+/**
+ * freezer_post_create - commit creation of a freezer cgroup
+ * @cgroup: cgroup being created
+ *
+ * We're committing to creation of @cgroup. Mark it online.
+ */
+static void freezer_post_create(struct cgroup *cgroup)
{
struct freezer *freezer = cgroup_freezer(cgroup);
+ spin_lock_irq(&freezer->lock);
+ freezer->state |= CGROUP_FREEZER_ONLINE;
+ spin_unlock_irq(&freezer->lock);
+}
+
+/**
+ * freezer_pre_destroy - initiate destruction of @cgroup
+ * @cgroup: cgroup being destroyed
+ *
+ * @cgroup is going away. Mark it dead and decrement system_freezing_count
+ * if it was holding one.
+ */
+static void freezer_pre_destroy(struct cgroup *cgroup)
+{
+ struct freezer *freezer = cgroup_freezer(cgroup);
+
+ spin_lock_irq(&freezer->lock);
+
if (freezer->state & CGROUP_FREEZING)
atomic_dec(&system_freezing_cnt);
- kfree(freezer);
+
+ freezer->state = 0;
+
+ spin_unlock_irq(&freezer->lock);
+}
+
+static void freezer_destroy(struct cgroup *cgroup)
+{
+ kfree(cgroup_freezer(cgroup));
}
/*
@@ -260,6 +293,9 @@
/* also synchronizes against task migration, see freezer_attach() */
lockdep_assert_held(&freezer->lock);
+ if (!(freezer->state & CGROUP_FREEZER_ONLINE))
+ return;
+
if (freeze) {
if (!(freezer->state & CGROUP_FREEZING))
atomic_inc(&system_freezing_cnt);
@@ -347,6 +383,8 @@
struct cgroup_subsys freezer_subsys = {
.name = "freezer",
.create = freezer_create,
+ .post_create = freezer_post_create,
+ .pre_destroy = freezer_pre_destroy,
.destroy = freezer_destroy,
.subsys_id = freezer_subsys_id,
.attach = freezer_attach,
