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>

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 1d4f471de8d54e508ff2fb9ca99d2be5924b5c03..e6571ca822a027fe0c6473a1a5be1e36eb3fa170 100644 (file)
--- 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);