4 files changed, 382 insertions, 1 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 788c4964c142..9a23bb098205 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -15,6 +15,7 @@
 #include <linux/cgroupstats.h>
 #include <linux/prio_heap.h>
 #include <linux/rwsem.h>
+#include <linux/idr.h>
 
 #ifdef CONFIG_CGROUPS
 
@@ -22,6 +23,7 @@ struct cgroupfs_root;
 struct cgroup_subsys;
 struct inode;
 struct cgroup;
+struct css_id;
 
 extern int cgroup_init_early(void);
 extern int cgroup_init(void);
@@ -63,6 +65,8 @@ struct cgroup_subsys_state {
         atomic_t refcnt;
 
         unsigned long flags;
+        /* ID for this css, if possible */
+        struct css_id *id;
 };
 
 /* bits in struct cgroup_subsys_state flags field */
@@ -373,6 +377,11 @@ struct cgroup_subsys {
         int active;
         int disabled;
         int early_init;
+        /*
+         * True if this subsys uses ID. ID is not available before cgroup_init()
+         * (not available in early_init time.)
+         */
+        bool use_id;
 #define MAX_CGROUP_TYPE_NAMELEN 32
         const char *name;
 
@@ -395,6 +404,9 @@ struct cgroup_subsys {
          */
         struct cgroupfs_root *root;
         struct list_head sibling;
+        /* used when use_id == true */
+        struct idr idr;
+        spinlock_t id_lock;
 };
 
 #define SUBSYS(_x) extern struct cgroup_subsys _x ## _subsys;
@@ -450,6 +462,44 @@ void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it);
 int cgroup_scan_tasks(struct cgroup_scanner *scan);
 int cgroup_attach_task(struct cgroup *, struct task_struct *);
 
+/*
+ * CSS ID is ID for cgroup_subsys_state structs under subsys. This only works
+ * if cgroup_subsys.use_id == true. It can be used for looking up and scanning.
+ * CSS ID is assigned at cgroup allocation (create) automatically
+ * and removed when subsys calls free_css_id() function. This is because
+ * the lifetime of cgroup_subsys_state is subsys's matter.
+ *
+ * Looking up and scanning function should be called under rcu_read_lock().
+ * Taking cgroup_mutex()/hierarchy_mutex() is not necessary for following calls.
+ * But the css returned by this routine can be "not populated yet" or "being
+ * destroyed". The caller should check css and cgroup's status.
+ */
+
+/*
+ * Typically Called at ->destroy(), or somewhere the subsys frees
+ * cgroup_subsys_state.
+ */
+void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css);
+
+/* Find a cgroup_subsys_state which has given ID */
+
+struct cgroup_subsys_state *css_lookup(struct cgroup_subsys *ss, int id);
+
+/*
+ * Get a cgroup whose id is greater than or equal to id under tree of root.
+ * Returning a cgroup_subsys_state or NULL.
+ */
+struct cgroup_subsys_state *css_get_next(struct cgroup_subsys *ss, int id,
+                struct cgroup_subsys_state *root, int *foundid);
+
+/* Returns true if root is ancestor of cg */
+bool css_is_ancestor(struct cgroup_subsys_state *cg,
+                     struct cgroup_subsys_state *root);
+
+/* Get id and depth of css */
+unsigned short css_id(struct cgroup_subsys_state *css);
+unsigned short css_depth(struct cgroup_subsys_state *css);
+
 #else /* !CONFIG_CGROUPS */
 
 static inline int cgroup_init_early(void) { return 0; }
diff --git a/include/linux/idr.h b/include/linux/idr.h
index dd846df8cd32..e968db71e33a 100644
--- a/include/linux/idr.h
+++ b/include/linux/idr.h
@@ -106,6 +106,7 @@ int idr_get_new(struct idr *idp, void *ptr, int *id);
 int idr_get_new_above(struct idr *idp, void *ptr, int starting_id, int *id);
 int idr_for_each(struct idr *idp,
                  int (*fn)(int id, void *p, void *data), void *data);
+void *idr_get_next(struct idr *idp, int *nextid);
 void *idr_replace(struct idr *idp, void *ptr, int id);
 void idr_remove(struct idr *idp, int id);
 void idr_remove_all(struct idr *idp);
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 27792bcb0758..d3c521137425 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -94,7 +94,6 @@ struct cgroupfs_root {
         char release_agent_path[PATH_MAX];
 };
 
-
 /*
  * The "rootnode" hierarchy is the "dummy hierarchy", reserved for the
  * subsystems that are otherwise unattached - it never has more than a
@@ -102,6 +101,39 @@ struct cgroupfs_root {
  */
 static struct cgroupfs_root rootnode;
 
+/*
+ * CSS ID -- ID per subsys's Cgroup Subsys State(CSS). used only when
+ * cgroup_subsys->use_id != 0.
+ */
+#define CSS_ID_MAX      (65535)
+struct css_id {
+        /*
+         * The css to which this ID points. This pointer is set to valid value
+         * after cgroup is populated. If cgroup is removed, this will be NULL.
+         * This pointer is expected to be RCU-safe because destroy()
+         * is called after synchronize_rcu(). But for safe use, css_is_removed()
+         * css_tryget() should be used for avoiding race.
+         */
+        struct cgroup_subsys_state *css;
+        /*
+         * ID of this css.
+         */
+        unsigned short id;
+        /*
+         * Depth in hierarchy which this ID belongs to.
+         */
+        unsigned short depth;
+        /*
+         * ID is freed by RCU. (and lookup routine is RCU safe.)
+         */
+        struct rcu_head rcu_head;
+        /*
+         * Hierarchy of CSS ID belongs to.
+         */
+        unsigned short stack[0]; /* Array of Length (depth+1) */
+};
+
+
 /* The list of hierarchy roots */
 
 static LIST_HEAD(roots);
@@ -185,6 +217,8 @@ struct cg_cgroup_link {
 static struct css_set init_css_set;
 static struct cg_cgroup_link init_css_set_link;
 
+static int cgroup_subsys_init_idr(struct cgroup_subsys *ss);
+
 /* css_set_lock protects the list of css_set objects, and the
  * chain of tasks off each css_set.  Nests outside task->alloc_lock
  * due to cgroup_iter_start() */
@@ -567,6 +601,9 @@ static struct backing_dev_info cgroup_backing_dev_info = {
         .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK,
 };
 
+static int alloc_css_id(struct cgroup_subsys *ss,
+                        struct cgroup *parent, struct cgroup *child);
+
 static struct inode *cgroup_new_inode(mode_t mode, struct super_block *sb)
 {
         struct inode *inode = new_inode(sb);
@@ -2327,6 +2364,17 @@ static int cgroup_populate_dir(struct cgroup *cgrp)
                 if (ss->populate && (err = ss->populate(ss, cgrp)) < 0)
                         return err;
         }
+        /* This cgroup is ready now */
+        for_each_subsys(cgrp->root, ss) {
+                struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
+                /*
+                 * Update id->css pointer and make this css visible from
+                 * CSS ID functions. This pointer will be dereferened
+                 * from RCU-read-side without locks.
+                 */
+                if (css->id)
+                        rcu_assign_pointer(css->id->css, css);
+        }
 
         return 0;
 }
@@ -2338,6 +2386,7 @@ static void init_cgroup_css(struct cgroup_subsys_state *css,
         css->cgroup = cgrp;
         atomic_set(&css->refcnt, 1);
         css->flags = 0;
+        css->id = NULL;
         if (cgrp == dummytop)
                 set_bit(CSS_ROOT, &css->flags);
         BUG_ON(cgrp->subsys[ss->subsys_id]);
@@ -2413,6 +2462,10 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
                         goto err_destroy;
                 }
                 init_cgroup_css(css, ss, cgrp);
+                if (ss->use_id)
+                        if (alloc_css_id(ss, parent, cgrp))
+                                goto err_destroy;
+                /* At error, ->destroy() callback has to free assigned ID. */
         }
 
         cgroup_lock_hierarchy(root);
@@ -2708,6 +2761,8 @@ int __init cgroup_init(void)
                 struct cgroup_subsys *ss = subsys[i];
                 if (!ss->early_init)
                         cgroup_init_subsys(ss);
+                if (ss->use_id)
+                        cgroup_subsys_init_idr(ss);
         }
 
         /* Add init_css_set to the hash table */
@@ -3242,3 +3297,232 @@ static int __init cgroup_disable(char *str)
         return 1;
 }
 __setup("cgroup_disable=", cgroup_disable);
+
+/*
+ * Functons for CSS ID.
+ */
+
+/*
+ *To get ID other than 0, this should be called when !cgroup_is_removed().
+ */
+unsigned short css_id(struct cgroup_subsys_state *css)
+{
+        struct css_id *cssid = rcu_dereference(css->id);
+
+        if (cssid)
+                return cssid->id;
+        return 0;
+}
+
+unsigned short css_depth(struct cgroup_subsys_state *css)
+{
+        struct css_id *cssid = rcu_dereference(css->id);
+
+        if (cssid)
+                return cssid->depth;
+        return 0;
+}
+
+bool css_is_ancestor(struct cgroup_subsys_state *child,
+                    struct cgroup_subsys_state *root)
+{
+        struct css_id *child_id = rcu_dereference(child->id);
+        struct css_id *root_id = rcu_dereference(root->id);
+
+        if (!child_id || !root_id || (child_id->depth < root_id->depth))
+                return false;
+        return child_id->stack[root_id->depth] == root_id->id;
+}
+
+static void __free_css_id_cb(struct rcu_head *head)
+{
+        struct css_id *id;
+
+        id = container_of(head, struct css_id, rcu_head);
+        kfree(id);
+}
+
+void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css)
+{
+        struct css_id *id = css->id;
+        /* When this is called before css_id initialization, id can be NULL */
+        if (!id)
+                return;
+
+        BUG_ON(!ss->use_id);
+
+        rcu_assign_pointer(id->css, NULL);
+        rcu_assign_pointer(css->id, NULL);
+        spin_lock(&ss->id_lock);
+        idr_remove(&ss->idr, id->id);
+        spin_unlock(&ss->id_lock);
+        call_rcu(&id->rcu_head, __free_css_id_cb);
+}
+
+/*
+ * This is called by init or create(). Then, calls to this function are
+ * always serialized (By cgroup_mutex() at create()).
+ */
+
+static struct css_id *get_new_cssid(struct cgroup_subsys *ss, int depth)
+{
+        struct css_id *newid;
+        int myid, error, size;
+
+        BUG_ON(!ss->use_id);
+
+        size = sizeof(*newid) + sizeof(unsigned short) * (depth + 1);
+        newid = kzalloc(size, GFP_KERNEL);
+        if (!newid)
+                return ERR_PTR(-ENOMEM);
+        /* get id */
+        if (unlikely(!idr_pre_get(&ss->idr, GFP_KERNEL))) {
+                error = -ENOMEM;
+                goto err_out;
+        }
+        spin_lock(&ss->id_lock);
+        /* Don't use 0. allocates an ID of 1-65535 */
+        error = idr_get_new_above(&ss->idr, newid, 1, &myid);
+        spin_unlock(&ss->id_lock);
+
+        /* Returns error when there are no free spaces for new ID.*/
+        if (error) {
+                error = -ENOSPC;
+                goto err_out;
+        }
+        if (myid > CSS_ID_MAX)
+                goto remove_idr;
+
+        newid->id = myid;
+        newid->depth = depth;
+        return newid;
+remove_idr:
+        error = -ENOSPC;
+        spin_lock(&ss->id_lock);
+        idr_remove(&ss->idr, myid);
+        spin_unlock(&ss->id_lock);
+err_out:
+        kfree(newid);
+        return ERR_PTR(error);
+
+}
+
+static int __init cgroup_subsys_init_idr(struct cgroup_subsys *ss)
+{
+        struct css_id *newid;
+        struct cgroup_subsys_state *rootcss;
+
+        spin_lock_init(&ss->id_lock);
+        idr_init(&ss->idr);
+
+        rootcss = init_css_set.subsys[ss->subsys_id];
+        newid = get_new_cssid(ss, 0);
+        if (IS_ERR(newid))
+                return PTR_ERR(newid);
+
+        newid->stack[0] = newid->id;
+        newid->css = rootcss;
+        rootcss->id = newid;
+        return 0;
+}
+
+static int alloc_css_id(struct cgroup_subsys *ss, struct cgroup *parent,
+                        struct cgroup *child)
+{
+        int subsys_id, i, depth = 0;
+        struct cgroup_subsys_state *parent_css, *child_css;
+        struct css_id *child_id, *parent_id = NULL;
+
+        subsys_id = ss->subsys_id;
+        parent_css = parent->subsys[subsys_id];
+        child_css = child->subsys[subsys_id];
+        depth = css_depth(parent_css) + 1;
+        parent_id = parent_css->id;
+
+        child_id = get_new_cssid(ss, depth);
+        if (IS_ERR(child_id))
+                return PTR_ERR(child_id);
+
+        for (i = 0; i < depth; i++)
+                child_id->stack[i] = parent_id->stack[i];
+        child_id->stack[depth] = child_id->id;
+        /*
+         * child_id->css pointer will be set after this cgroup is available
+         * see cgroup_populate_dir()
+         */
+        rcu_assign_pointer(child_css->id, child_id);
+
+        return 0;
+}
+
+/**
+ * css_lookup - lookup css by id
+ * @ss: cgroup subsys to be looked into.
+ * @id: the id
+ *
+ * Returns pointer to cgroup_subsys_state if there is valid one with id.
+ * NULL if not. Should be called under rcu_read_lock()
+ */
+struct cgroup_subsys_state *css_lookup(struct cgroup_subsys *ss, int id)
+{
+        struct css_id *cssid = NULL;
+
+        BUG_ON(!ss->use_id);
+        cssid = idr_find(&ss->idr, id);
+
+        if (unlikely(!cssid))
+                return NULL;
+
+        return rcu_dereference(cssid->css);
+}
+
+/**
+ * css_get_next - lookup next cgroup under specified hierarchy.
+ * @ss: pointer to subsystem
+ * @id: current position of iteration.
+ * @root: pointer to css. search tree under this.
+ * @foundid: position of found object.
+ *
+ * Search next css under the specified hierarchy of rootid. Calling under
+ * rcu_read_lock() is necessary. Returns NULL if it reaches the end.
+ */
+struct cgroup_subsys_state *
+css_get_next(struct cgroup_subsys *ss, int id,
+             struct cgroup_subsys_state *root, int *foundid)
+{
+        struct cgroup_subsys_state *ret = NULL;
+        struct css_id *tmp;
+        int tmpid;
+        int rootid = css_id(root);
+        int depth = css_depth(root);
+
+        if (!rootid)
+                return NULL;
+
+        BUG_ON(!ss->use_id);
+        /* fill start point for scan */
+        tmpid = id;
+        while (1) {
+                /*
+                 * scan next entry from bitmap(tree), tmpid is updated after
+                 * idr_get_next().
+                 */
+                spin_lock(&ss->id_lock);
+                tmp = idr_get_next(&ss->idr, &tmpid);
+                spin_unlock(&ss->id_lock);
+
+                if (!tmp)
+                        break;
+                if (tmp->depth >= depth && tmp->stack[depth] == rootid) {
+                        ret = rcu_dereference(tmp->css);
+                        if (ret) {
+                                *foundid = tmpid;
+                                break;
+                        }
+                }
+                /* continue to scan from next id */
+                tmpid = tmpid + 1;
+        }
+        return ret;
+}
+
diff --git a/lib/idr.c b/lib/idr.c
index dab4bca86f5d..80ca9aca038b 100644
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -579,6 +579,52 @@ int idr_for_each(struct idr *idp,
 EXPORT_SYMBOL(idr_for_each);
 
 /**
+ * idr_get_next - lookup next object of id to given id.
+ * @idp: idr handle
+ * @id:  pointer to lookup key
+ *
+ * Returns pointer to registered object with id, which is next number to
+ * given id.
+ */
+
+void *idr_get_next(struct idr *idp, int *nextidp)
+{
+        struct idr_layer *p, *pa[MAX_LEVEL];
+        struct idr_layer **paa = &pa[0];
+        int id = *nextidp;
+        int n, max;
+
+        /* find first ent */
+        n = idp->layers * IDR_BITS;
+        max = 1 << n;
+        p = rcu_dereference(idp->top);
+        if (!p)
+                return NULL;
+
+        while (id < max) {
+                while (n > 0 && p) {
+                        n -= IDR_BITS;
+                        *paa++ = p;
+                        p = rcu_dereference(p->ary[(id >> n) & IDR_MASK]);
+                }
+
+                if (p) {
+                        *nextidp = id;
+                        return p;
+                }
+
+                id += 1 << n;
+                while (n < fls(id)) {
+                        n += IDR_BITS;
+                        p = *--paa;
+                }
+        }
+        return NULL;
+}
+
+
+
+/**
  * idr_replace - replace pointer for given id
  * @idp: idr handle
  * @ptr: pointer you want associated with the id