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>

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 8118a31..900af59 100644 (file)
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -203,6 +203,7 @@ struct cgroup {
 
        /* For RCU-protected deletion */
        struct rcu_head rcu_head;
+       struct work_struct free_work;
 
        /* List of events which userspace want to receive */
        struct list_head event_list;

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index af99391..02e4f20 100644 (file)
--- 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);