Currently, css (cgroup_subsys_state) lifetime is tied to that of the
associated cgroup. With the planned unified hierarchy, css's will be
dynamically created and destroyed within the lifetime of a cgroup. To
enable such usages, css's will be individually RCU protected instead
of being tied to the cgroup.
cgroup->css_kill_cnt is used during cgroup destruction to wait for css
reference count disable; however, this model doesn't work once css's
lifetimes are managed separately from cgroup's. This patch replaces
it with cgroup->nr_css which is an cgroup_mutex protected integer
counting the number of attached css's. The count is incremented from
online_css() and decremented after refcnt kill is confirmed. If the
count reaches zero and the cgroup is marked dead, the second stage of
cgroup destruction is kicked off. If a cgroup doesn't have any css
attached at the time of rmdir, cgroup_destroy_locked() now invokes the
second stage directly as no css kill confirmation would happen.
cgroup_offline_fn() - the second step of cgroup destruction - is
renamed to cgroup_destroy_css_killed() and now expects to be called
with cgroup_mutex held.
While this patch changes how css destruction is punted to work items,
it shouldn't change any visible behavior.
Signed-off-by: Tejun Heo <t...@kernel.org>
---
include/linux/cgroup.h | 4 +++-
kernel/cgroup.c | 52 +++++++++++++++++++++++++++-----------------------
2 files changed, 31 insertions(+), 25 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index eb200b5..80dca87 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -171,6 +171,9 @@ struct cgroup {
*/
int id;
+ /* the number of attached css's */
+ int nr_css;
+
/*
* We link our 'sibling' struct into our parent's 'children'.
* Our children link their 'sibling' into our 'children'.
@@ -234,7 +237,6 @@ struct cgroup {
/* For css percpu_ref killing and RCU-protected deletion */
struct rcu_head rcu_head;
struct work_struct destroy_work;
- atomic_t css_kill_cnt;
/* List of events which userspace want to receive */
struct list_head event_list;
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 88b1095..484af35 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -218,7 +218,7 @@ static int need_forkexit_callback __read_mostly;
static struct cftype cgroup_base_files[];
-static void cgroup_offline_fn(struct work_struct *work);
+static void cgroup_destroy_css_killed(struct cgroup *cgrp);
static int cgroup_destroy_locked(struct cgroup *cgrp);
static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
bool is_add);
@@ -4335,6 +4335,7 @@ static int online_css(struct cgroup_subsys_state *css)
ret = ss->css_online(css);
if (!ret) {
css->flags |= CSS_ONLINE;
+ css->cgroup->nr_css++;
rcu_assign_pointer(css->cgroup->subsys[ss->subsys_id], css);
}
return ret;
@@ -4541,16 +4542,6 @@ static int cgroup_mkdir(struct inode *dir, struct dentry
*dentry, umode_t mode)
return cgroup_create(c_parent, dentry, mode | S_IFDIR);
}
-static void cgroup_css_killed(struct cgroup *cgrp)
-{
- if (!atomic_dec_and_test(&cgrp->css_kill_cnt))
- return;
-
- /* percpu ref's of all css's are killed, kick off the next step */
- INIT_WORK(&cgrp->destroy_work, cgroup_offline_fn);
- schedule_work(&cgrp->destroy_work);
-}
-
/*
* This is called when the refcnt of a css is confirmed to be killed.
* css_tryget() is now guaranteed to fail.
@@ -4561,7 +4552,17 @@ static void css_killed_work_fn(struct work_struct *work)
container_of(work, struct cgroup_subsys_state, destroy_work);
struct cgroup *cgrp = css->cgroup;
- cgroup_css_killed(cgrp);
+ mutex_lock(&cgroup_mutex);
+
+ /*
+ * 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))
+ cgroup_destroy_css_killed(cgrp);
+
+ mutex_unlock(&cgroup_mutex);
}
/* css kill confirmation processing requires process context, bounce */
@@ -4630,11 +4631,10 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
* 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 schedules cgroup_offline_fn() to perform the rest of
- * destruction once the percpu refs of all css's are confirmed to
- * be killed.
+ * 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.
*/
- atomic_set(&cgrp->css_kill_cnt, 1);
for_each_root_subsys(cgrp->root, ss) {
struct cgroup_subsys_state *css = cgroup_css(cgrp,
ss->subsys_id);
@@ -4644,10 +4644,8 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
*/
percpu_ref_get(&css->refcnt);
- atomic_inc(&cgrp->css_kill_cnt);
percpu_ref_kill_and_confirm(&css->refcnt, css_killed_ref_fn);
}
- cgroup_css_killed(cgrp);
/*
* Mark @cgrp dead. This prevents further task migration and child
@@ -4665,6 +4663,15 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
raw_spin_unlock(&release_list_lock);
/*
+ * If @cgrp has css's attached, the second stage of cgroup
+ * destruction is kicked off from css_killed_work_fn() after the
+ * refs of all attached css's are killed. If @cgrp doesn't have
+ * any css, we kick it off here.
+ */
+ if (!cgrp->nr_css)
+ cgroup_destroy_css_killed(cgrp);
+
+ /*
* Clear and remove @cgrp directory. The removal puts the base ref
* but we aren't quite done with @cgrp yet, so hold onto it.
*/
@@ -4689,7 +4696,7 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
};
/**
- * cgroup_offline_fn - the second step of cgroup destruction
+ * cgroup_destroy_css_killed - the second step of cgroup destruction
* @work: cgroup->destroy_free_work
*
* This function is invoked from a work item for a cgroup which is being
@@ -4698,14 +4705,13 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
* is the second step of destruction described in the comment above
* cgroup_destroy_locked().
*/
-static void cgroup_offline_fn(struct work_struct *work)
+static void cgroup_destroy_css_killed(struct cgroup *cgrp)
{
- struct cgroup *cgrp = container_of(work, struct cgroup, destroy_work);
struct cgroup *parent = cgrp->parent;
struct dentry *d = cgrp->dentry;
struct cgroup_subsys *ss;
- mutex_lock(&cgroup_mutex);
+ lockdep_assert_held(&cgroup_mutex);
/*
* css_tryget() is guaranteed to fail now. Tell subsystems to
@@ -4739,8 +4745,6 @@ static void cgroup_offline_fn(struct work_struct *work)
set_bit(CGRP_RELEASABLE, &parent->flags);
check_for_release(parent);
-
- mutex_unlock(&cgroup_mutex);
}
static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
--
1.8.3.1
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