cgroup->count tracks the number of css_sets associated with the cgroup
and used only to verify that no css_set is associated when the cgroup
is being destroyed. It's superflous as the destruction path can
simply check whether cgroup->cset_links is empty instead.
Drop cgroup->count and check ->cset_links directly from
cgroup_destroy_locked().
Signed-off-by: Tejun Heo <t...@kernel.org>
---
include/linux/cgroup.h | 6 ------
kernel/cgroup.c | 21 +++++----------------
2 files changed, 5 insertions(+), 22 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index c86a93a..81bfd02 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -169,12 +169,6 @@ struct cgroup_name {
struct cgroup {
unsigned long flags; /* "unsigned long" so bitops work */
- /*
- * count users of this cgroup. >0 means busy, but doesn't
- * necessarily indicate the number of tasks in the cgroup
- */
- atomic_t count;
-
int id; /* ida allocated in-hierarchy ID */
/*
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 22f9729..062653f 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -408,8 +408,7 @@ static void __put_css_set(struct css_set *cset, int
taskexit)
list_del(&link->cgrp_link);
/* @cgrp can't go away while we're holding css_set_lock */
- if (atomic_dec_and_test(&cgrp->count) &&
- notify_on_release(cgrp)) {
+ if (list_empty(&cgrp->cset_links) && notify_on_release(cgrp)) {
if (taskexit)
set_bit(CGRP_RELEASABLE, &cgrp->flags);
check_for_release(cgrp);
@@ -616,7 +615,6 @@ static void link_css_set(struct list_head *tmp_links,
struct css_set *cset,
link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link);
link->cset = cset;
link->cgrp = cgrp;
- atomic_inc(&cgrp->count);
list_move(&link->cset_link, &cgrp->cset_links);
/*
* Always add links to the tail of the list so that the list
@@ -4373,11 +4371,11 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
lockdep_assert_held(&cgroup_mutex);
/*
- * css_set_lock prevents @cgrp from being removed while
- * __put_css_set() is in progress.
+ * css_set_lock synchronizes access to ->cset_links and prevents
+ * @cgrp from being removed while __put_css_set() is in progress.
*/
read_lock(&css_set_lock);
- empty = !atomic_read(&cgrp->count) && list_empty(&cgrp->children);
+ empty = list_empty(&cgrp->cset_links) && list_empty(&cgrp->children);
read_unlock(&css_set_lock);
if (!empty)
return -EBUSY;
@@ -5057,7 +5055,7 @@ void cgroup_exit(struct task_struct *tsk, int
run_callbacks)
static void check_for_release(struct cgroup *cgrp)
{
if (cgroup_is_releasable(cgrp) &&
- !atomic_read(&cgrp->count) && list_empty(&cgrp->children)) {
+ list_empty(&cgrp->cset_links) && list_empty(&cgrp->children)) {
/*
* Control Group is currently removeable. If it's not
* already queued for a userspace notification, queue
@@ -5425,11 +5423,6 @@ static void debug_css_free(struct cgroup *cont)
kfree(cont->subsys[debug_subsys_id]);
}
-static u64 cgroup_refcount_read(struct cgroup *cont, struct cftype *cft)
-{
- return atomic_read(&cont->count);
-}
-
static u64 debug_taskcount_read(struct cgroup *cont, struct cftype *cft)
{
return cgroup_task_count(cont);
@@ -5511,10 +5504,6 @@ static u64 releasable_read(struct cgroup *cgrp, struct
cftype *cft)
static struct cftype debug_files[] = {
{
- .name = "cgroup_refcount",
- .read_u64 = cgroup_refcount_read,
- },
- {
.name = "taskcount",
.read_u64 = debug_taskcount_read,
},
--
1.8.2.1
--
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