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>

1 files changed, 25 insertions, 15 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 5679cb1ce43f..4412d9694f13 100644
--- 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);