cgroup: make serial_nr_cursor available throughout cgroup.c

The next patch will use it to determine if a cgroup is newly created
while we're iterating the cgroup hierarchy.

tj: Rephrased the comment on top of cgroup_serial_nr_cursor.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 10 insertions, 8 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 1d4f471de8d5..e6571ca822a0 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -198,6 +198,15 @@ static DEFINE_IDR(cgroup_hierarchy_idr);
 
 static struct cgroup_name root_cgroup_name = { .name = "/" };
 
+/*
+ * Assign a monotonically increasing serial number to cgroups.  It
+ * guarantees cgroups with bigger numbers are newer than those with smaller
+ * numbers.  Also, as cgroups are always appended to the parent's
+ * ->children list, it guarantees that sibling cgroups are always sorted in
+ * the ascending serial number order on the list.
+ */
+static atomic64_t cgroup_serial_nr_cursor = ATOMIC64_INIT(0);
+
 /* This flag indicates whether tasks in the fork and exit paths should
  * check for fork/exit handlers to call. This avoids us having to do
  * extra work in the fork/exit path if none of the subsystems need to
@@ -4222,7 +4231,6 @@ static void offline_css(struct cgroup_subsys *ss, struct cgroup *cgrp)
 static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
                              umode_t mode)
 {
-        static atomic64_t serial_nr_cursor = ATOMIC64_INIT(0);
         struct cgroup *cgrp;
         struct cgroup_name *name;
         struct cgroupfs_root *root = parent->root;
@@ -4309,13 +4317,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
                 goto err_free_all;
         lockdep_assert_held(&dentry->d_inode->i_mutex);
 
-        /*
-         * Assign a monotonically increasing serial number.  With the list
-         * appending below, it guarantees that sibling cgroups are always
-         * sorted in the ascending serial number order on the parent's
-         * ->children.
-         */
-        cgrp->serial_nr = atomic64_inc_return(&serial_nr_cursor);
+        cgrp->serial_nr = atomic64_inc_return(&cgroup_serial_nr_cursor);
 
         /* allocation complete, commit to creation */
         list_add_tail(&cgrp->allcg_node, &root->allcg_list);