cgroup: add cgroup->id

With the introduction of generic cgroup hierarchy iterators, css_id is
being phased out.  It was unnecessarily complex, id'ing the wrong
thing (cgroups need IDs, not CSSes) and has other oddities like not
being available at ->css_alloc().

This patch adds cgroup->id, which is a simple per-hierarchy
ida-allocated ID which is assigned before ->css_alloc() and released
after ->css_free().

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

1 files changed, 14 insertions, 1 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 96719f73e95d..6db01417d39a 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -138,6 +138,9 @@ struct cgroupfs_root {
         /* Hierarchy-specific flags */
         unsigned long flags;
 
+        /* IDs for cgroups in this hierarchy */
+        struct ida cgroup_ida;
+
         /* The path to use for release notifications. */
         char release_agent_path[PATH_MAX];
 
@@ -890,6 +893,7 @@ static void cgroup_diput(struct dentry *dentry, struct inode *inode)
 
                 simple_xattrs_free(&cgrp->xattrs);
 
+                ida_simple_remove(&cgrp->root->cgroup_ida, cgrp->id);
                 kfree_rcu(cgrp, rcu_head);
         } else {
                 struct cfent *cfe = __d_cfe(dentry);
@@ -1465,6 +1469,7 @@ static struct cgroupfs_root *cgroup_root_from_opts(struct cgroup_sb_opts *opts)
 
         root->subsys_mask = opts->subsys_mask;
         root->flags = opts->flags;
+        ida_init(&root->cgroup_ida);
         if (opts->release_agent)
                 strcpy(root->release_agent_path, opts->release_agent);
         if (opts->name)
@@ -1483,6 +1488,7 @@ static void cgroup_drop_root(struct cgroupfs_root *root)
         spin_lock(&hierarchy_id_lock);
         ida_remove(&hierarchy_ida, root->hierarchy_id);
         spin_unlock(&hierarchy_id_lock);
+        ida_destroy(&root->cgroup_ida);
         kfree(root);
 }
 
@@ -4093,10 +4099,15 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
         struct cgroup_subsys *ss;
         struct super_block *sb = root->sb;
 
+        /* allocate the cgroup and its ID, 0 is reserved for the root */
         cgrp = kzalloc(sizeof(*cgrp), GFP_KERNEL);
         if (!cgrp)
                 return -ENOMEM;
 
+        cgrp->id = ida_simple_get(&root->cgroup_ida, 1, 0, GFP_KERNEL);
+        if (cgrp->id < 0)
+                goto err_free_cgrp;
+
         /*
          * Only live parents can have children.  Note that the liveliness
          * check isn't strictly necessary because cgroup_mkdir() and
@@ -4106,7 +4117,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
          */
         if (!cgroup_lock_live_group(parent)) {
                 err = -ENODEV;
-                goto err_free_cgrp;
+                goto err_free_id;
         }
 
         /* Grab a reference on the superblock so the hierarchy doesn't
@@ -4198,6 +4209,8 @@ err_free_all:
         mutex_unlock(&cgroup_mutex);
         /* Release the reference count that we took on the superblock */
         deactivate_super(sb);
+err_free_id:
+        ida_simple_remove(&root->cgroup_ida, cgrp->id);
 err_free_cgrp:
         kfree(cgrp);
         return err;