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>

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index c798997..82cf9e6 100644 (file)
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -159,6 +159,8 @@ struct cgroup {
         */
        atomic_t count;
 
+       int id;                         /* ida allocated in-hierarchy ID */
+
        /*
         * We link our 'sibling' struct into our parent's 'children'.
         * Our children link their 'sibling' into our 'children'.

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 96719f7..6db0141 100644 (file)
--- 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;