cgroup: misc preps for kernfs conversion

* Un-inline seq_css().  After kernfs conversion, the function will
  need to dereference internal data structures.

* Add cgroup_get/put_root() and replace direct super_block->s_active
  manipulatinos with them.  These will be converted to kernfs_root
  refcnting.

* Add cgroup_get/put() and replace dget/put() on cgrp->dentry with
  them.  These will be converted to kernfs refcnting.

* Update current_css_set_cg_links_read() to use cgroup_name() instead
  of reaching into the dentry name.  The end result is the same.

These changes don't make functional differences but will make
transition to kernfs easier.

v2: Rebased on top of 0ab02ca8f887 ("cgroup: protect modifications to
    cgroup_idr with cgroup_mutex").

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

2 files changed, 55 insertions, 38 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 06f577764414..523277871913 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -516,18 +516,14 @@ static inline ino_t cgroup_ino(struct cgroup *cgrp)
                 return 0;
 }
 
-static inline struct cgroup_subsys_state *seq_css(struct seq_file *seq)
-{
-        struct cgroup_open_file *of = seq->private;
-        return of->cfe->css;
-}
-
 static inline struct cftype *seq_cft(struct seq_file *seq)
 {
         struct cgroup_open_file *of = seq->private;
         return of->cfe->type;
 }
 
+struct cgroup_subsys_state *seq_css(struct seq_file *seq);
+
 int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
 int cgroup_rm_cftypes(struct cftype *cfts);
 
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 11f7a05e791e..9e9e8fd632d8 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -169,6 +169,7 @@ static int need_forkexit_callback __read_mostly;
 
 static struct cftype cgroup_base_files[];
 
+static void cgroup_put(struct cgroup *cgrp);
 static void cgroup_destroy_css_killed(struct cgroup *cgrp);
 static int cgroup_destroy_locked(struct cgroup *cgrp);
 static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
@@ -204,6 +205,13 @@ static inline bool cgroup_is_dead(const struct cgroup *cgrp)
         return test_bit(CGRP_DEAD, &cgrp->flags);
 }
 
+struct cgroup_subsys_state *seq_css(struct seq_file *seq)
+{
+        struct cgroup_open_file *of = seq->private;
+        return of->cfe->css;
+}
+EXPORT_SYMBOL_GPL(seq_css);
+
 /**
  * cgroup_is_descendant - test ancestry
  * @cgrp: the cgroup to be tested
@@ -682,6 +690,16 @@ static struct css_set *find_css_set(struct css_set *old_cset,
         return cset;
 }
 
+static void cgroup_get_root(struct cgroupfs_root *root)
+{
+        atomic_inc(&root->sb->s_active);
+}
+
+static void cgroup_put_root(struct cgroupfs_root *root)
+{
+        deactivate_super(root->sb);
+}
+
 /*
  * Return the cgroup for "task" from the given hierarchy. Must be
  * called with cgroup_mutex held.
@@ -837,18 +855,14 @@ static void cgroup_free_fn(struct work_struct *work)
         mutex_unlock(&cgroup_mutex);
 
         /*
-         * We get a ref to the parent's dentry, and put the ref when
-         * this cgroup is being freed, so it's guaranteed that the
-         * parent won't be destroyed before its children.
+         * We get a ref to the parent, and put the ref when this cgroup is
+         * being freed, so it's guaranteed that the parent won't be
+         * destroyed before its children.
          */
-        dput(cgrp->parent->dentry);
+        cgroup_put(cgrp->parent);
 
-        /*
-         * Drop the active superblock reference that we took when we
-         * created the cgroup. This will free cgrp->root, if we are
-         * holding the last reference to @sb.
-         */
-        deactivate_super(cgrp->root->sb);
+        /* put the root reference that we took when we created the cgroup */
+        cgroup_put_root(cgrp->root);
 
         cgroup_pidlist_destroy_all(cgrp);
 
@@ -866,6 +880,11 @@ static void cgroup_free_rcu(struct rcu_head *head)
         queue_work(cgroup_destroy_wq, &cgrp->destroy_work);
 }
 
+static void cgroup_get(struct cgroup *cgrp)
+{
+        dget(cgrp->dentry);
+}
+
 static void cgroup_diput(struct dentry *dentry, struct inode *inode)
 {
         /* is dentry a directory ? if so, kfree() associated cgroup */
@@ -899,6 +918,11 @@ static void cgroup_diput(struct dentry *dentry, struct inode *inode)
         iput(inode);
 }
 
+static void cgroup_put(struct cgroup *cgrp)
+{
+        dput(cgrp->dentry);
+}
+
 static void remove_dir(struct dentry *d)
 {
         struct dentry *parent = dget(d->d_parent);
@@ -2724,7 +2748,7 @@ static int cgroup_cfts_commit(struct cftype *cfts, bool is_add)
         struct cgroup_subsys *ss = cfts[0].ss;
         struct cgroup *root = &ss->root->top_cgroup;
         struct super_block *sb = ss->root->sb;
-        struct dentry *prev = NULL;
+        struct cgroup *prev = NULL;
         struct inode *inode;
         struct cgroup_subsys_state *css;
         u64 update_before;
@@ -2754,9 +2778,10 @@ static int cgroup_cfts_commit(struct cftype *cfts, bool is_add)
                         continue;
 
                 inode = cgrp->dentry->d_inode;
-                dget(cgrp->dentry);
-                dput(prev);
-                prev = cgrp->dentry;
+                cgroup_get(cgrp);
+                if (prev)
+                        cgroup_put(prev);
+                prev = cgrp;
 
                 mutex_unlock(&cgroup_tree_mutex);
                 mutex_lock(&inode->i_mutex);
@@ -2768,8 +2793,8 @@ static int cgroup_cfts_commit(struct cftype *cfts, bool is_add)
                         break;
         }
         mutex_unlock(&cgroup_tree_mutex);
-        dput(prev);
-        deactivate_super(sb);
+        cgroup_put(prev);
+        cgroup_put_root(ss->root);
         return ret;
 }
 
@@ -3863,11 +3888,9 @@ static int cgroup_write_notify_on_release(struct cgroup_subsys_state *css,
  */
 static void cgroup_dput(struct cgroup *cgrp)
 {
-        struct super_block *sb = cgrp->root->sb;
-
-        atomic_inc(&sb->s_active);
-        dput(cgrp->dentry);
-        deactivate_super(sb);
+        cgroup_get_root(cgrp->root);
+        cgroup_put(cgrp);
+        cgroup_put_root(cgrp->root);
 }
 
 static u64 cgroup_clone_children_read(struct cgroup_subsys_state *css,
@@ -4118,7 +4141,7 @@ static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss)
         if (err)
                 goto err_free;
 
-        dget(cgrp->dentry);
+        cgroup_get(cgrp);
         css_get(css->parent);
 
         if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
@@ -4197,7 +4220,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
          * can be done outside cgroup_mutex, since the sb can't
          * disappear while someone has an open control file on the
          * fs */
-        atomic_inc(&sb->s_active);
+        cgroup_get_root(root);
 
         init_cgroup_housekeeping(cgrp);
 
@@ -4231,7 +4254,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
         root->number_of_cgroups++;
 
         /* hold a ref to the parent's dentry */
-        dget(parent->dentry);
+        cgroup_get(parent);
 
         /*
          * @cgrp is now fully operational.  If something fails after this
@@ -4261,7 +4284,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
 err_free_id:
         idr_remove(&root->cgroup_idr, cgrp->id);
         /* Release the reference count that we took on the superblock */
-        deactivate_super(sb);
+        cgroup_put_root(root);
 err_unlock:
         mutex_unlock(&cgroup_mutex);
 err_unlock_tree:
@@ -4493,7 +4516,6 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
 static void cgroup_destroy_css_killed(struct cgroup *cgrp)
 {
         struct cgroup *parent = cgrp->parent;
-        struct dentry *d = cgrp->dentry;
 
         lockdep_assert_held(&cgroup_tree_mutex);
         lockdep_assert_held(&cgroup_mutex);
@@ -4501,7 +4523,7 @@ static void cgroup_destroy_css_killed(struct cgroup *cgrp)
         /* delete this cgroup from parent->children */
         list_del_rcu(&cgrp->sibling);
 
-        dput(d);
+        cgroup_put(cgrp);
 
         set_bit(CGRP_RELEASABLE, &parent->flags);
         check_for_release(parent);
@@ -5161,12 +5183,11 @@ static int current_css_set_cg_links_read(struct seq_file *seq, void *v)
         cset = rcu_dereference(current->cgroups);
         list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
                 struct cgroup *c = link->cgrp;
-                const char *name;
+                const char *name = "?";
+
+                if (c != cgroup_dummy_top)
+                        name = cgroup_name(c);
 
-                if (c->dentry)
-                        name = c->dentry->d_name.name;
-                else
-                        name = "?";
                 seq_printf(seq, "Root %d group %s\n",
                            c->root->hierarchy_id, name);
         }