cgroup: separate out cgroup_destroy_locked()

Separate out cgroup_destroy_locked() from cgroup_destroy().  This will
be later used in cgroup_create() failure path.

While at it, add lockdep asserts on i_mutex and cgroup_mutex, and move
@d and @parent assignments to their declarations.

This patch doesn't introduce any functional difference.

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

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 5679cb1..4412d96 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -242,6 +242,8 @@ static DEFINE_SPINLOCK(hierarchy_id_lock);
  */
 static int need_forkexit_callback __read_mostly;
 
+static int cgroup_destroy_locked(struct cgroup *cgrp);
+
 #ifdef CONFIG_PROVE_LOCKING
 int cgroup_lock_is_held(void)
 {
@@ -4209,22 +4211,20 @@ static int cgroup_has_css_refs(struct cgroup *cgrp)
        return 0;
 }
 
-static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
+static int cgroup_destroy_locked(struct cgroup *cgrp)
+       __releases(&cgroup_mutex) __acquires(&cgroup_mutex)
 {
-       struct cgroup *cgrp = dentry->d_fsdata;
-       struct dentry *d;
-       struct cgroup *parent;
+       struct dentry *d = cgrp->dentry;
+       struct cgroup *parent = cgrp->parent;
        DEFINE_WAIT(wait);
        struct cgroup_event *event, *tmp;
        struct cgroup_subsys *ss;
 
-       /* the vfs holds both inode->i_mutex already */
-       mutex_lock(&cgroup_mutex);
-       parent = cgrp->parent;
-       if (atomic_read(&cgrp->count) || !list_empty(&cgrp->children)) {
-               mutex_unlock(&cgroup_mutex);
+       lockdep_assert_held(&d->d_inode->i_mutex);
+       lockdep_assert_held(&cgroup_mutex);
+
+       if (atomic_read(&cgrp->count) || !list_empty(&cgrp->children))
                return -EBUSY;
-       }
 
        /*
         * Block new css_tryget() by deactivating refcnt and mark @cgrp
@@ -4243,7 +4243,9 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
        /*
         * Tell subsystems to initate destruction.  pre_destroy() should be
         * called with cgroup_mutex unlocked.  See 3fa59dfbc3 ("cgroup: fix
-        * potential deadlock in pre_destroy") for details.
+        * potential deadlock in pre_destroy") for details.  This temporary
+        * unlocking should go away once cgroup_mutex is unexported from
+        * controllers.
         */
        mutex_unlock(&cgroup_mutex);
        for_each_subsys(cgrp->root, ss)
@@ -4268,11 +4270,9 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
 
        /* delete this cgroup from parent->children */
        list_del_rcu(&cgrp->sibling);
-
        list_del_init(&cgrp->allcg_node);
 
-       d = dget(cgrp->dentry);
-
+       dget(d);
        cgroup_d_remove_dir(d);
        dput(d);
 
@@ -4293,10 +4293,20 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
        }
        spin_unlock(&cgrp->event_list_lock);
 
-       mutex_unlock(&cgroup_mutex);
        return 0;
 }
 
+static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
+{
+       int ret;
+
+       mutex_lock(&cgroup_mutex);
+       ret = cgroup_destroy_locked(dentry->d_fsdata);
+       mutex_unlock(&cgroup_mutex);
+
+       return ret;
+}
+
 static void __init_or_module cgroup_init_cftsets(struct cgroup_subsys *ss)
 {
        INIT_LIST_HEAD(&ss->cftsets);