cgroup: remove synchronize_rcu() from cgroup_diput()

Free cgroup via call_rcu(). The actual work is done through
workqueue.

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

1 files changed, 43 insertions, 29 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index af993919aa04..02e4f201472e 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -852,12 +852,52 @@ static struct inode *cgroup_new_inode(umode_t mode, struct super_block *sb)
         return inode;
 }
 
+static void cgroup_free_fn(struct work_struct *work)
+{
+        struct cgroup *cgrp = container_of(work, struct cgroup, free_work);
+        struct cgroup_subsys *ss;
+
+        mutex_lock(&cgroup_mutex);
+        /*
+         * Release the subsystem state objects.
+         */
+        for_each_subsys(cgrp->root, ss)
+                ss->css_free(cgrp);
+
+        cgrp->root->number_of_cgroups--;
+        mutex_unlock(&cgroup_mutex);
+
+        /*
+         * Drop the active superblock reference that we took when we
+         * created the cgroup
+         */
+        deactivate_super(cgrp->root->sb);
+
+        /*
+         * if we're getting rid of the cgroup, refcount should ensure
+         * that there are no pidlists left.
+         */
+        BUG_ON(!list_empty(&cgrp->pidlists));
+
+        simple_xattrs_free(&cgrp->xattrs);
+
+        ida_simple_remove(&cgrp->root->cgroup_ida, cgrp->id);
+        kfree(cgrp);
+}
+
+static void cgroup_free_rcu(struct rcu_head *head)
+{
+        struct cgroup *cgrp = container_of(head, struct cgroup, rcu_head);
+
+        schedule_work(&cgrp->free_work);
+}
+
 static void cgroup_diput(struct dentry *dentry, struct inode *inode)
 {
         /* is dentry a directory ? if so, kfree() associated cgroup */
         if (S_ISDIR(inode->i_mode)) {
                 struct cgroup *cgrp = dentry->d_fsdata;
-                struct cgroup_subsys *ss;
+
                 BUG_ON(!(cgroup_is_removed(cgrp)));
                 /* It's possible for external users to be holding css
                  * reference counts on a cgroup; css_put() needs to
@@ -865,34 +905,7 @@ static void cgroup_diput(struct dentry *dentry, struct inode *inode)
                  * the reference count in order to know if it needs to
                  * queue the cgroup to be handled by the release
                  * agent */
-                synchronize_rcu();
-
-                mutex_lock(&cgroup_mutex);
-                /*
-                 * Release the subsystem state objects.
-                 */
-                for_each_subsys(cgrp->root, ss)
-                        ss->css_free(cgrp);
-
-                cgrp->root->number_of_cgroups--;
-                mutex_unlock(&cgroup_mutex);
-
-                /*
-                 * Drop the active superblock reference that we took when we
-                 * created the cgroup
-                 */
-                deactivate_super(cgrp->root->sb);
-
-                /*
-                 * if we're getting rid of the cgroup, refcount should ensure
-                 * that there are no pidlists left.
-                 */
-                BUG_ON(!list_empty(&cgrp->pidlists));
-
-                simple_xattrs_free(&cgrp->xattrs);
-
-                ida_simple_remove(&cgrp->root->cgroup_ida, cgrp->id);
-                kfree(cgrp);
+                call_rcu(&cgrp->rcu_head, cgroup_free_rcu);
         } else {
                 struct cfent *cfe = __d_cfe(dentry);
                 struct cgroup *cgrp = dentry->d_parent->d_fsdata;
@@ -1391,6 +1404,7 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
         INIT_LIST_HEAD(&cgrp->allcg_node);
         INIT_LIST_HEAD(&cgrp->release_list);
         INIT_LIST_HEAD(&cgrp->pidlists);
+        INIT_WORK(&cgrp->free_work, cgroup_free_fn);
         mutex_init(&cgrp->pidlist_mutex);
         INIT_LIST_HEAD(&cgrp->event_list);
         spin_lock_init(&cgrp->event_list_lock);