Gitweb:     
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=817929ec274bcfe771586d338bb31d1659615686
Commit:     817929ec274bcfe771586d338bb31d1659615686
Parent:     a424316ca154317367c7ddf89997d1c80e4a8051
Author:     Paul Menage <[EMAIL PROTECTED]>
AuthorDate: Thu Oct 18 23:39:36 2007 -0700
Committer:  Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Fri Oct 19 11:53:36 2007 -0700

    Task Control Groups: shared cgroup subsystem group arrays
    
    Replace the struct css_set embedded in task_struct with a pointer; all tasks
    that have the same set of memberships across all hierarchies will share a
    css_set object, and will be linked via their css_sets field to the "tasks"
    list_head in the css_set.
    
    Assuming that many tasks share the same cgroup assignments, this reduces
    overall space usage and keeps the size of the task_struct down (three 
pointers
    added to task_struct compared to a non-cgroups kernel, no matter how many
    subsystems are registered).
    
    [EMAIL PROTECTED]: fix a printk]
    [EMAIL PROTECTED]: build fix]
    Signed-off-by: Paul Menage <[EMAIL PROTECTED]>
    Cc: Serge E. Hallyn <[EMAIL PROTECTED]>
    Cc: "Eric W. Biederman" <[EMAIL PROTECTED]>
    Cc: Dave Hansen <[EMAIL PROTECTED]>
    Cc: Balbir Singh <[EMAIL PROTECTED]>
    Cc: Paul Jackson <[EMAIL PROTECTED]>
    Cc: Kirill Korotaev <[EMAIL PROTECTED]>
    Cc: Herbert Poetzl <[EMAIL PROTECTED]>
    Cc: Srivatsa Vaddagiri <[EMAIL PROTECTED]>
    Cc: Cedric Le Goater <[EMAIL PROTECTED]>
    Cc: Serge E. Hallyn <[EMAIL PROTECTED]>
    Cc: "Eric W. Biederman" <[EMAIL PROTECTED]>
    Cc: Dave Hansen <[EMAIL PROTECTED]>
    Cc: Balbir Singh <[EMAIL PROTECTED]>
    Cc: Paul Jackson <[EMAIL PROTECTED]>
    Cc: Kirill Korotaev <[EMAIL PROTECTED]>
    Cc: Herbert Poetzl <[EMAIL PROTECTED]>
    Cc: Srivatsa Vaddagiri <[EMAIL PROTECTED]>
    Cc: Cedric Le Goater <[EMAIL PROTECTED]>
    Cc: KAMEZAWA Hiroyuki <[EMAIL PROTECTED]>
    Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
    Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
 Documentation/cgroups.txt |   14 +-
 include/linux/cgroup.h    |   89 ++++++-
 include/linux/sched.h     |   33 +--
 kernel/cgroup.c           |  649 +++++++++++++++++++++++++++++++++++++--------
 kernel/fork.c             |    1 +
 5 files changed, 632 insertions(+), 154 deletions(-)

diff --git a/Documentation/cgroups.txt b/Documentation/cgroups.txt
index 553727c..98a26f8 100644
--- a/Documentation/cgroups.txt
+++ b/Documentation/cgroups.txt
@@ -176,7 +176,9 @@ Control Groups extends the kernel as follows:
    subsystem state is something that's expected to happen frequently
    and in performance-critical code, whereas operations that require a
    task's actual cgroup assignments (in particular, moving between
-   cgroups) are less common.
+   cgroups) are less common. A linked list runs through the cg_list
+   field of each task_struct using the css_set, anchored at
+   css_set->tasks.
 
  - A cgroup hierarchy filesystem can be mounted  for browsing and
    manipulation from user space.
@@ -252,6 +254,16 @@ linear search to locate an appropriate existing css_set, 
so isn't
 very efficient. A future version will use a hash table for better
 performance.
 
+To allow access from a cgroup to the css_sets (and hence tasks)
+that comprise it, a set of cg_cgroup_link objects form a lattice;
+each cg_cgroup_link is linked into a list of cg_cgroup_links for
+a single cgroup on its cont_link_list field, and a list of
+cg_cgroup_links for a single css_set on its cg_link_list.
+
+Thus the set of tasks in a cgroup can be listed by iterating over
+each css_set that references the cgroup, and sub-iterating over
+each css_set's task set.
+
 The use of a Linux virtual file system (vfs) to represent the
 cgroup hierarchy provides for a familiar permission and name space
 for cgroups, with a minimum of additional kernel code.
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index a955356..836b355 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -27,10 +27,19 @@ extern void cgroup_lock(void);
 extern void cgroup_unlock(void);
 extern void cgroup_fork(struct task_struct *p);
 extern void cgroup_fork_callbacks(struct task_struct *p);
+extern void cgroup_post_fork(struct task_struct *p);
 extern void cgroup_exit(struct task_struct *p, int run_callbacks);
 
 extern struct file_operations proc_cgroup_operations;
 
+/* Define the enumeration of all cgroup subsystems */
+#define SUBSYS(_x) _x ## _subsys_id,
+enum cgroup_subsys_id {
+#include <linux/cgroup_subsys.h>
+       CGROUP_SUBSYS_COUNT
+};
+#undef SUBSYS
+
 /* Per-subsystem/per-cgroup state maintained by the system. */
 struct cgroup_subsys_state {
        /* The cgroup that this subsystem is attached to. Useful
@@ -97,6 +106,52 @@ struct cgroup {
 
        struct cgroupfs_root *root;
        struct cgroup *top_cgroup;
+
+       /*
+        * List of cg_cgroup_links pointing at css_sets with
+        * tasks in this cgroup. Protected by css_set_lock
+        */
+       struct list_head css_sets;
+};
+
+/* A css_set is a structure holding pointers to a set of
+ * cgroup_subsys_state objects. This saves space in the task struct
+ * object and speeds up fork()/exit(), since a single inc/dec and a
+ * list_add()/del() can bump the reference count on the entire
+ * cgroup set for a task.
+ */
+
+struct css_set {
+
+       /* Reference count */
+       struct kref ref;
+
+       /*
+        * List running through all cgroup groups. Protected by
+        * css_set_lock
+        */
+       struct list_head list;
+
+       /*
+        * List running through all tasks using this cgroup
+        * group. Protected by css_set_lock
+        */
+       struct list_head tasks;
+
+       /*
+        * List of cg_cgroup_link objects on link chains from
+        * cgroups referenced from this css_set. Protected by
+        * css_set_lock
+        */
+       struct list_head cg_links;
+
+       /*
+        * Set of subsystem states, one for each subsystem. This array
+        * is immutable after creation apart from the init_css_set
+        * during subsystem registration (at boot time).
+        */
+       struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];
+
 };
 
 /* struct cftype:
@@ -157,15 +212,7 @@ int cgroup_is_removed(const struct cgroup *cont);
 
 int cgroup_path(const struct cgroup *cont, char *buf, int buflen);
 
-int __cgroup_task_count(const struct cgroup *cont);
-static inline int cgroup_task_count(const struct cgroup *cont)
-{
-       int task_count;
-       rcu_read_lock();
-       task_count = __cgroup_task_count(cont);
-       rcu_read_unlock();
-       return task_count;
-}
+int cgroup_task_count(const struct cgroup *cont);
 
 /* Return true if the cgroup is a descendant of the current cgroup */
 int cgroup_is_descendant(const struct cgroup *cont);
@@ -213,7 +260,7 @@ static inline struct cgroup_subsys_state 
*cgroup_subsys_state(
 static inline struct cgroup_subsys_state *task_subsys_state(
        struct task_struct *task, int subsys_id)
 {
-       return rcu_dereference(task->cgroups.subsys[subsys_id]);
+       return rcu_dereference(task->cgroups->subsys[subsys_id]);
 }
 
 static inline struct cgroup* task_cgroup(struct task_struct *task,
@@ -226,6 +273,27 @@ int cgroup_path(const struct cgroup *cont, char *buf, int 
buflen);
 
 int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *ss);
 
+/* A cgroup_iter should be treated as an opaque object */
+struct cgroup_iter {
+       struct list_head *cg_link;
+       struct list_head *task;
+};
+
+/* To iterate across the tasks in a cgroup:
+ *
+ * 1) call cgroup_iter_start to intialize an iterator
+ *
+ * 2) call cgroup_iter_next() to retrieve member tasks until it
+ *    returns NULL or until you want to end the iteration
+ *
+ * 3) call cgroup_iter_end() to destroy the iterator.
+ */
+void cgroup_iter_start(struct cgroup *cont, struct cgroup_iter *it);
+struct task_struct *cgroup_iter_next(struct cgroup *cont,
+                                       struct cgroup_iter *it);
+void cgroup_iter_end(struct cgroup *cont, struct cgroup_iter *it);
+
+
 #else /* !CONFIG_CGROUPS */
 
 static inline int cgroup_init_early(void) { return 0; }
@@ -233,6 +301,7 @@ static inline int cgroup_init(void) { return 0; }
 static inline void cgroup_init_smp(void) {}
 static inline void cgroup_fork(struct task_struct *p) {}
 static inline void cgroup_fork_callbacks(struct task_struct *p) {}
+static inline void cgroup_post_fork(struct task_struct *p) {}
 static inline void cgroup_exit(struct task_struct *p, int callbacks) {}
 
 static inline void cgroup_lock(void) {}
diff --git a/include/linux/sched.h b/include/linux/sched.h
index af2ed4b..1aa1cfa 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -894,34 +894,6 @@ struct sched_entity {
 #endif
 };
 
-#ifdef CONFIG_CGROUPS
-
-#define SUBSYS(_x) _x ## _subsys_id,
-enum cgroup_subsys_id {
-#include <linux/cgroup_subsys.h>
-       CGROUP_SUBSYS_COUNT
-};
-#undef SUBSYS
-
-/* A css_set is a structure holding pointers to a set of
- * cgroup_subsys_state objects.
- */
-
-struct css_set {
-
-       /* Set of subsystem states, one for each subsystem. NULL for
-        * subsystems that aren't part of this hierarchy. These
-        * pointers reduce the number of dereferences required to get
-        * from a task to its state for a given cgroup, but result
-        * in increased space usage if tasks are in wildly different
-        * groupings across different hierarchies. This array is
-        * immutable after creation */
-       struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];
-
-};
-
-#endif /* CONFIG_CGROUPS */
-
 struct task_struct {
        volatile long state;    /* -1 unrunnable, 0 runnable, >0 stopped */
        void *stack;
@@ -1159,7 +1131,10 @@ struct task_struct {
        int cpuset_mem_spread_rotor;
 #endif
 #ifdef CONFIG_CGROUPS
-       struct css_set cgroups;
+       /* Control Group info protected by css_set_lock */
+       struct css_set *cgroups;
+       /* cg_list protected by css_set_lock and tsk->alloc_lock */
+       struct list_head cg_list;
 #endif
 #ifdef CONFIG_FUTEX
        struct robust_list_head __user *robust_list;
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index db245f1..883928c 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -36,6 +36,7 @@
 #include <linux/proc_fs.h>
 #include <linux/rcupdate.h>
 #include <linux/sched.h>
+#include <linux/backing-dev.h>
 #include <linux/seq_file.h>
 #include <linux/slab.h>
 #include <linux/magic.h>
@@ -95,6 +96,7 @@ static struct cgroupfs_root rootnode;
 /* The list of hierarchy roots */
 
 static LIST_HEAD(roots);
+static int root_count;
 
 /* dummytop is a shorthand for the dummy hierarchy's top cgroup */
 #define dummytop (&rootnode.top_cgroup)
@@ -133,12 +135,49 @@ list_for_each_entry(_ss, &_root->subsys_list, sibling)
 #define for_each_root(_root) \
 list_for_each_entry(_root, &roots, root_list)
 
-/* Each task_struct has an embedded css_set, so the get/put
- * operation simply takes a reference count on all the cgroups
- * referenced by subsystems in this css_set. This can end up
- * multiple-counting some cgroups, but that's OK - the ref-count is
- * just a busy/not-busy indicator; ensuring that we only count each
- * cgroup once would require taking a global lock to ensure that no
+/* Link structure for associating css_set objects with cgroups */
+struct cg_cgroup_link {
+       /*
+        * List running through cg_cgroup_links associated with a
+        * cgroup, anchored on cgroup->css_sets
+        */
+       struct list_head cont_link_list;
+       /*
+        * List running through cg_cgroup_links pointing at a
+        * single css_set object, anchored on css_set->cg_links
+        */
+       struct list_head cg_link_list;
+       struct css_set *cg;
+};
+
+/* The default css_set - used by init and its children prior to any
+ * hierarchies being mounted. It contains a pointer to the root state
+ * for each subsystem. Also used to anchor the list of css_sets. Not
+ * reference-counted, to improve performance when child cgroups
+ * haven't been created.
+ */
+
+static struct css_set init_css_set;
+static struct cg_cgroup_link init_css_set_link;
+
+/* 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() */
+static DEFINE_RWLOCK(css_set_lock);
+static int css_set_count;
+
+/* We don't maintain the lists running through each css_set to its
+ * task until after the first call to cgroup_iter_start(). This
+ * reduces the fork()/exit() overhead for people who have cgroups
+ * compiled into their kernel but not actually in use */
+static int use_task_css_set_links;
+
+/* When we create or destroy a css_set, the operation simply
+ * takes/releases a reference count on all the cgroups referenced
+ * by subsystems in this css_set. This can end up multiple-counting
+ * some cgroups, but that's OK - the ref-count is just a
+ * busy/not-busy indicator; ensuring that we only count each cgroup
+ * once would require taking a global lock to ensure that no
  * subsystems moved between hierarchies while we were doing so.
  *
  * Possible TODO: decide at boot time based on the number of
@@ -146,18 +185,230 @@ list_for_each_entry(_root, &roots, root_list)
  * it's better for performance to ref-count every subsystem, or to
  * take a global lock and only add one ref count to each hierarchy.
  */
-static void get_css_set(struct css_set *cg)
+
+/*
+ * unlink a css_set from the list and free it
+ */
+static void release_css_set(struct kref *k)
 {
+       struct css_set *cg = container_of(k, struct css_set, ref);
        int i;
+
+       write_lock(&css_set_lock);
+       list_del(&cg->list);
+       css_set_count--;
+       while (!list_empty(&cg->cg_links)) {
+               struct cg_cgroup_link *link;
+               link = list_entry(cg->cg_links.next,
+                                 struct cg_cgroup_link, cg_link_list);
+               list_del(&link->cg_link_list);
+               list_del(&link->cont_link_list);
+               kfree(link);
+       }
+       write_unlock(&css_set_lock);
        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++)
-               atomic_inc(&cg->subsys[i]->cgroup->count);
+               atomic_dec(&cg->subsys[i]->cgroup->count);
+       kfree(cg);
 }
 
-static void put_css_set(struct css_set *cg)
+/*
+ * refcounted get/put for css_set objects
+ */
+static inline void get_css_set(struct css_set *cg)
+{
+       kref_get(&cg->ref);
+}
+
+static inline void put_css_set(struct css_set *cg)
+{
+       kref_put(&cg->ref, release_css_set);
+}
+
+/*
+ * find_existing_css_set() is a helper for
+ * find_css_set(), and checks to see whether an existing
+ * css_set is suitable. This currently walks a linked-list for
+ * simplicity; a later patch will use a hash table for better
+ * performance
+ *
+ * oldcg: the cgroup group that we're using before the cgroup
+ * transition
+ *
+ * cont: the cgroup that we're moving into
+ *
+ * template: location in which to build the desired set of subsystem
+ * state objects for the new cgroup group
+ */
+
+static struct css_set *find_existing_css_set(
+       struct css_set *oldcg,
+       struct cgroup *cont,
+       struct cgroup_subsys_state *template[])
 {
        int i;
-       for (i = 0; i < CGROUP_SUBSYS_COUNT; i++)
-               atomic_dec(&cg->subsys[i]->cgroup->count);
+       struct cgroupfs_root *root = cont->root;
+       struct list_head *l = &init_css_set.list;
+
+       /* Built the set of subsystem state objects that we want to
+        * see in the new css_set */
+       for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+               if (root->subsys_bits & (1ull << i)) {
+                       /* Subsystem is in this hierarchy. So we want
+                        * the subsystem state from the new
+                        * cgroup */
+                       template[i] = cont->subsys[i];
+               } else {
+                       /* Subsystem is not in this hierarchy, so we
+                        * don't want to change the subsystem state */
+                       template[i] = oldcg->subsys[i];
+               }
+       }
+
+       /* Look through existing cgroup groups to find one to reuse */
+       do {
+               struct css_set *cg =
+                       list_entry(l, struct css_set, list);
+
+               if (!memcmp(template, cg->subsys, sizeof(cg->subsys))) {
+                       /* All subsystems matched */
+                       return cg;
+               }
+               /* Try the next cgroup group */
+               l = l->next;
+       } while (l != &init_css_set.list);
+
+       /* No existing cgroup group matched */
+       return NULL;
+}
+
+/*
+ * allocate_cg_links() allocates "count" cg_cgroup_link structures
+ * and chains them on tmp through their cont_link_list fields. Returns 0 on
+ * success or a negative error
+ */
+
+static int allocate_cg_links(int count, struct list_head *tmp)
+{
+       struct cg_cgroup_link *link;
+       int i;
+       INIT_LIST_HEAD(tmp);
+       for (i = 0; i < count; i++) {
+               link = kmalloc(sizeof(*link), GFP_KERNEL);
+               if (!link) {
+                       while (!list_empty(tmp)) {
+                               link = list_entry(tmp->next,
+                                                 struct cg_cgroup_link,
+                                                 cont_link_list);
+                               list_del(&link->cont_link_list);
+                               kfree(link);
+                       }
+                       return -ENOMEM;
+               }
+               list_add(&link->cont_link_list, tmp);
+       }
+       return 0;
+}
+
+static void free_cg_links(struct list_head *tmp)
+{
+       while (!list_empty(tmp)) {
+               struct cg_cgroup_link *link;
+               link = list_entry(tmp->next,
+                                 struct cg_cgroup_link,
+                                 cont_link_list);
+               list_del(&link->cont_link_list);
+               kfree(link);
+       }
+}
+
+/*
+ * find_css_set() takes an existing cgroup group and a
+ * cgroup object, and returns a css_set object that's
+ * equivalent to the old group, but with the given cgroup
+ * substituted into the appropriate hierarchy. Must be called with
+ * cgroup_mutex held
+ */
+
+static struct css_set *find_css_set(
+       struct css_set *oldcg, struct cgroup *cont)
+{
+       struct css_set *res;
+       struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT];
+       int i;
+
+       struct list_head tmp_cg_links;
+       struct cg_cgroup_link *link;
+
+       /* First see if we already have a cgroup group that matches
+        * the desired set */
+       write_lock(&css_set_lock);
+       res = find_existing_css_set(oldcg, cont, template);
+       if (res)
+               get_css_set(res);
+       write_unlock(&css_set_lock);
+
+       if (res)
+               return res;
+
+       res = kmalloc(sizeof(*res), GFP_KERNEL);
+       if (!res)
+               return NULL;
+
+       /* Allocate all the cg_cgroup_link objects that we'll need */
+       if (allocate_cg_links(root_count, &tmp_cg_links) < 0) {
+               kfree(res);
+               return NULL;
+       }
+
+       kref_init(&res->ref);
+       INIT_LIST_HEAD(&res->cg_links);
+       INIT_LIST_HEAD(&res->tasks);
+
+       /* Copy the set of subsystem state objects generated in
+        * find_existing_css_set() */
+       memcpy(res->subsys, template, sizeof(res->subsys));
+
+       write_lock(&css_set_lock);
+       /* Add reference counts and links from the new css_set. */
+       for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+               struct cgroup *cont = res->subsys[i]->cgroup;
+               struct cgroup_subsys *ss = subsys[i];
+               atomic_inc(&cont->count);
+               /*
+                * We want to add a link once per cgroup, so we
+                * only do it for the first subsystem in each
+                * hierarchy
+                */
+               if (ss->root->subsys_list.next == &ss->sibling) {
+                       BUG_ON(list_empty(&tmp_cg_links));
+                       link = list_entry(tmp_cg_links.next,
+                                         struct cg_cgroup_link,
+                                         cont_link_list);
+                       list_del(&link->cont_link_list);
+                       list_add(&link->cont_link_list, &cont->css_sets);
+                       link->cg = res;
+                       list_add(&link->cg_link_list, &res->cg_links);
+               }
+       }
+       if (list_empty(&rootnode.subsys_list)) {
+               link = list_entry(tmp_cg_links.next,
+                                 struct cg_cgroup_link,
+                                 cont_link_list);
+               list_del(&link->cont_link_list);
+               list_add(&link->cont_link_list, &dummytop->css_sets);
+               link->cg = res;
+               list_add(&link->cg_link_list, &res->cg_links);
+       }
+
+       BUG_ON(!list_empty(&tmp_cg_links));
+
+       /* Link this cgroup group into the list */
+       list_add(&res->list, &init_css_set.list);
+       css_set_count++;
+       INIT_LIST_HEAD(&res->tasks);
+       write_unlock(&css_set_lock);
+
+       return res;
 }
 
 /*
@@ -504,6 +755,7 @@ static void init_cgroup_root(struct cgroupfs_root *root)
        cont->top_cgroup = cont;
        INIT_LIST_HEAD(&cont->sibling);
        INIT_LIST_HEAD(&cont->children);
+       INIT_LIST_HEAD(&cont->css_sets);
 }
 
 static int cgroup_test_super(struct super_block *sb, void *data)
@@ -573,6 +825,8 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
        int ret = 0;
        struct super_block *sb;
        struct cgroupfs_root *root;
+       struct list_head tmp_cg_links, *l;
+       INIT_LIST_HEAD(&tmp_cg_links);
 
        /* First find the desired set of subsystems */
        ret = parse_cgroupfs_options(data, &opts);
@@ -602,18 +856,36 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
        } else {
                /* New superblock */
                struct cgroup *cont = &root->top_cgroup;
+               struct inode *inode;
 
                BUG_ON(sb->s_root != NULL);
 
                ret = cgroup_get_rootdir(sb);
                if (ret)
                        goto drop_new_super;
+               inode = sb->s_root->d_inode;
 
+               mutex_lock(&inode->i_mutex);
                mutex_lock(&cgroup_mutex);
 
+               /*
+                * We're accessing css_set_count without locking
+                * css_set_lock here, but that's OK - it can only be
+                * increased by someone holding cgroup_lock, and
+                * that's us. The worst that can happen is that we
+                * have some link structures left over
+                */
+               ret = allocate_cg_links(css_set_count, &tmp_cg_links);
+               if (ret) {
+                       mutex_unlock(&cgroup_mutex);
+                       mutex_unlock(&inode->i_mutex);
+                       goto drop_new_super;
+               }
+
                ret = rebind_subsystems(root, root->subsys_bits);
                if (ret == -EBUSY) {
                        mutex_unlock(&cgroup_mutex);
+                       mutex_unlock(&inode->i_mutex);
                        goto drop_new_super;
                }
 
@@ -621,24 +893,40 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
                BUG_ON(ret);
 
                list_add(&root->root_list, &roots);
+               root_count++;
 
                sb->s_root->d_fsdata = &root->top_cgroup;
                root->top_cgroup.dentry = sb->s_root;
 
+               /* Link the top cgroup in this hierarchy into all
+                * the css_set objects */
+               write_lock(&css_set_lock);
+               l = &init_css_set.list;
+               do {
+                       struct css_set *cg;
+                       struct cg_cgroup_link *link;
+                       cg = list_entry(l, struct css_set, list);
+                       BUG_ON(list_empty(&tmp_cg_links));
+                       link = list_entry(tmp_cg_links.next,
+                                         struct cg_cgroup_link,
+                                         cont_link_list);
+                       list_del(&link->cont_link_list);
+                       link->cg = cg;
+                       list_add(&link->cont_link_list,
+                                &root->top_cgroup.css_sets);
+                       list_add(&link->cg_link_list, &cg->cg_links);
+                       l = l->next;
+               } while (l != &init_css_set.list);
+               write_unlock(&css_set_lock);
+
+               free_cg_links(&tmp_cg_links);
+
                BUG_ON(!list_empty(&cont->sibling));
                BUG_ON(!list_empty(&cont->children));
                BUG_ON(root->number_of_cgroups != 1);
 
-               /*
-                * I believe that it's safe to nest i_mutex inside
-                * cgroup_mutex in this case, since no-one else can
-                * be accessing this directory yet. But we still need
-                * to teach lockdep that this is the case - currently
-                * a cgroupfs remount triggers a lockdep warning
-                */
-               mutex_lock(&cont->dentry->d_inode->i_mutex);
                cgroup_populate_dir(cont);
-               mutex_unlock(&cont->dentry->d_inode->i_mutex);
+               mutex_unlock(&inode->i_mutex);
                mutex_unlock(&cgroup_mutex);
        }
 
@@ -647,6 +935,7 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
  drop_new_super:
        up_write(&sb->s_umount);
        deactivate_super(sb);
+       free_cg_links(&tmp_cg_links);
        return ret;
 }
 
@@ -668,8 +957,25 @@ static void cgroup_kill_sb(struct super_block *sb) {
        /* Shouldn't be able to fail ... */
        BUG_ON(ret);
 
-       if (!list_empty(&root->root_list))
+       /*
+        * Release all the links from css_sets to this hierarchy's
+        * root cgroup
+        */
+       write_lock(&css_set_lock);
+       while (!list_empty(&cont->css_sets)) {
+               struct cg_cgroup_link *link;
+               link = list_entry(cont->css_sets.next,
+                                 struct cg_cgroup_link, cont_link_list);
+               list_del(&link->cg_link_list);
+               list_del(&link->cont_link_list);
+               kfree(link);
+       }
+       write_unlock(&css_set_lock);
+
+       if (!list_empty(&root->root_list)) {
                list_del(&root->root_list);
+               root_count--;
+       }
        mutex_unlock(&cgroup_mutex);
 
        kfree(root);
@@ -762,9 +1068,9 @@ static int attach_task(struct cgroup *cont, struct 
task_struct *tsk)
        int retval = 0;
        struct cgroup_subsys *ss;
        struct cgroup *oldcont;
-       struct css_set *cg = &tsk->cgroups;
+       struct css_set *cg = tsk->cgroups;
+       struct css_set *newcg;
        struct cgroupfs_root *root = cont->root;
-       int i;
        int subsys_id;
 
        get_first_subsys(cont, NULL, &subsys_id);
@@ -783,26 +1089,32 @@ static int attach_task(struct cgroup *cont, struct 
task_struct *tsk)
                }
        }
 
+       /*
+        * Locate or allocate a new css_set for this task,
+        * based on its final set of cgroups
+        */
+       newcg = find_css_set(cg, cont);
+       if (!newcg) {
+               return -ENOMEM;
+       }
+
        task_lock(tsk);
        if (tsk->flags & PF_EXITING) {
                task_unlock(tsk);
+               put_css_set(newcg);
                return -ESRCH;
        }
-       /* Update the css_set pointers for the subsystems in this
-        * hierarchy */
-       for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
-               if (root->subsys_bits & (1ull << i)) {
-                       /* Subsystem is in this hierarchy. So we want
-                        * the subsystem state from the new
-                        * cgroup. Transfer the refcount from the
-                        * old to the new */
-                       atomic_inc(&cont->count);
-                       atomic_dec(&cg->subsys[i]->cgroup->count);
-                       rcu_assign_pointer(cg->subsys[i], cont->subsys[i]);
-               }
-       }
+       rcu_assign_pointer(tsk->cgroups, newcg);
        task_unlock(tsk);
 
+       /* Update the css_set linked lists if we're using them */
+       write_lock(&css_set_lock);
+       if (!list_empty(&tsk->cg_list)) {
+               list_del(&tsk->cg_list);
+               list_add(&tsk->cg_list, &newcg->tasks);
+       }
+       write_unlock(&css_set_lock);
+
        for_each_subsys(root, ss) {
                if (ss->attach) {
                        ss->attach(ss, cont, oldcont, tsk);
@@ -810,6 +1122,7 @@ static int attach_task(struct cgroup *cont, struct 
task_struct *tsk)
        }
 
        synchronize_rcu();
+       put_css_set(cg);
        return 0;
 }
 
@@ -1069,7 +1382,7 @@ static int cgroup_create_file(struct dentry *dentry, int 
mode,
 
                /* start with the directory inode held, so that we can
                 * populate it without racing with another mkdir */
-               mutex_lock(&inode->i_mutex);
+               mutex_lock_nested(&inode->i_mutex, I_MUTEX_CHILD);
        } else if (S_ISREG(mode)) {
                inode->i_size = 0;
                inode->i_fop = &cgroup_file_operations;
@@ -1148,28 +1461,102 @@ int cgroup_add_files(struct cgroup *cont,
        return 0;
 }
 
-/* Count the number of tasks in a cgroup. Could be made more
- * time-efficient but less space-efficient with more linked lists
- * running through each cgroup and the css_set structures that
- * referenced it. Must be called with tasklist_lock held for read or
- * write or in an rcu critical section.
- */
-int __cgroup_task_count(const struct cgroup *cont)
+/* Count the number of tasks in a cgroup. */
+
+int cgroup_task_count(const struct cgroup *cont)
 {
        int count = 0;
-       struct task_struct *g, *p;
-       struct cgroup_subsys_state *css;
-       int subsys_id;
-
-       get_first_subsys(cont, &css, &subsys_id);
-       do_each_thread(g, p) {
-               if (task_subsys_state(p, subsys_id) == css)
-                       count ++;
-       } while_each_thread(g, p);
+       struct list_head *l;
+
+       read_lock(&css_set_lock);
+       l = cont->css_sets.next;
+       while (l != &cont->css_sets) {
+               struct cg_cgroup_link *link =
+                       list_entry(l, struct cg_cgroup_link, cont_link_list);
+               count += atomic_read(&link->cg->ref.refcount);
+               l = l->next;
+       }
+       read_unlock(&css_set_lock);
        return count;
 }
 
 /*
+ * Advance a list_head iterator.  The iterator should be positioned at
+ * the start of a css_set
+ */
+static void cgroup_advance_iter(struct cgroup *cont,
+                                         struct cgroup_iter *it)
+{
+       struct list_head *l = it->cg_link;
+       struct cg_cgroup_link *link;
+       struct css_set *cg;
+
+       /* Advance to the next non-empty css_set */
+       do {
+               l = l->next;
+               if (l == &cont->css_sets) {
+                       it->cg_link = NULL;
+                       return;
+               }
+               link = list_entry(l, struct cg_cgroup_link, cont_link_list);
+               cg = link->cg;
+       } while (list_empty(&cg->tasks));
+       it->cg_link = l;
+       it->task = cg->tasks.next;
+}
+
+void cgroup_iter_start(struct cgroup *cont, struct cgroup_iter *it)
+{
+       /*
+        * The first time anyone tries to iterate across a cgroup,
+        * we need to enable the list linking each css_set to its
+        * tasks, and fix up all existing tasks.
+        */
+       if (!use_task_css_set_links) {
+               struct task_struct *p, *g;
+               write_lock(&css_set_lock);
+               use_task_css_set_links = 1;
+               do_each_thread(g, p) {
+                       task_lock(p);
+                       if (list_empty(&p->cg_list))
+                               list_add(&p->cg_list, &p->cgroups->tasks);
+                       task_unlock(p);
+               } while_each_thread(g, p);
+               write_unlock(&css_set_lock);
+       }
+       read_lock(&css_set_lock);
+       it->cg_link = &cont->css_sets;
+       cgroup_advance_iter(cont, it);
+}
+
+struct task_struct *cgroup_iter_next(struct cgroup *cont,
+                                       struct cgroup_iter *it)
+{
+       struct task_struct *res;
+       struct list_head *l = it->task;
+
+       /* If the iterator cg is NULL, we have no tasks */
+       if (!it->cg_link)
+               return NULL;
+       res = list_entry(l, struct task_struct, cg_list);
+       /* Advance iterator to find next entry */
+       l = l->next;
+       if (l == &res->cgroups->tasks) {
+               /* We reached the end of this task list - move on to
+                * the next cg_cgroup_link */
+               cgroup_advance_iter(cont, it);
+       } else {
+               it->task = l;
+       }
+       return res;
+}
+
+void cgroup_iter_end(struct cgroup *cont, struct cgroup_iter *it)
+{
+       read_unlock(&css_set_lock);
+}
+
+/*
  * Stuff for reading the 'tasks' file.
  *
  * Reading this file can return large amounts of data if a cgroup has
@@ -1198,22 +1585,15 @@ struct ctr_struct {
 static int pid_array_load(pid_t *pidarray, int npids, struct cgroup *cont)
 {
        int n = 0;
-       struct task_struct *g, *p;
-       struct cgroup_subsys_state *css;
-       int subsys_id;
-
-       get_first_subsys(cont, &css, &subsys_id);
-       rcu_read_lock();
-       do_each_thread(g, p) {
-               if (task_subsys_state(p, subsys_id) == css) {
-                       pidarray[n++] = pid_nr(task_pid(p));
-                       if (unlikely(n == npids))
-                               goto array_full;
-               }
-       } while_each_thread(g, p);
-
-array_full:
-       rcu_read_unlock();
+       struct cgroup_iter it;
+       struct task_struct *tsk;
+       cgroup_iter_start(cont, &it);
+       while ((tsk = cgroup_iter_next(cont, &it))) {
+               if (unlikely(n == npids))
+                       break;
+               pidarray[n++] = pid_nr(task_pid(tsk));
+       }
+       cgroup_iter_end(cont, &it);
        return n;
 }
 
@@ -1398,6 +1778,7 @@ static long cgroup_create(struct cgroup *parent, struct 
dentry *dentry,
        cont->flags = 0;
        INIT_LIST_HEAD(&cont->sibling);
        INIT_LIST_HEAD(&cont->children);
+       INIT_LIST_HEAD(&cont->css_sets);
 
        cont->parent = parent;
        cont->root = parent->root;
@@ -1529,8 +1910,8 @@ static int cgroup_rmdir(struct inode *unused_dir, struct 
dentry *dentry)
 
 static void cgroup_init_subsys(struct cgroup_subsys *ss)
 {
-       struct task_struct *g, *p;
        struct cgroup_subsys_state *css;
+       struct list_head *l;
        printk(KERN_ERR "Initializing cgroup subsys %s\n", ss->name);
 
        /* Create the top cgroup state for this subsystem */
@@ -1540,26 +1921,32 @@ static void cgroup_init_subsys(struct cgroup_subsys *ss)
        BUG_ON(IS_ERR(css));
        init_cgroup_css(css, ss, dummytop);
 
-       /* Update all tasks to contain a subsys pointer to this state
-        * - since the subsystem is newly registered, all tasks are in
-        * the subsystem's top cgroup. */
+       /* Update all cgroup groups to contain a subsys
+        * pointer to this state - since the subsystem is
+        * newly registered, all tasks and hence all cgroup
+        * groups are in the subsystem's top cgroup. */
+       write_lock(&css_set_lock);
+       l = &init_css_set.list;
+       do {
+               struct css_set *cg =
+                       list_entry(l, struct css_set, list);
+               cg->subsys[ss->subsys_id] = dummytop->subsys[ss->subsys_id];
+               l = l->next;
+       } while (l != &init_css_set.list);
+       write_unlock(&css_set_lock);
 
        /* If this subsystem requested that it be notified with fork
         * events, we should send it one now for every process in the
         * system */
+       if (ss->fork) {
+               struct task_struct *g, *p;
 
-       read_lock(&tasklist_lock);
-       init_task.cgroups.subsys[ss->subsys_id] = css;
-       if (ss->fork)
-               ss->fork(ss, &init_task);
-
-       do_each_thread(g, p) {
-               printk(KERN_INFO "Setting task %p css to %p (%d)\n", css, p, 
p->pid);
-               p->cgroups.subsys[ss->subsys_id] = css;
-               if (ss->fork)
-                       ss->fork(ss, p);
-       } while_each_thread(g, p);
-       read_unlock(&tasklist_lock);
+               read_lock(&tasklist_lock);
+               do_each_thread(g, p) {
+                       ss->fork(ss, p);
+               } while_each_thread(g, p);
+               read_unlock(&tasklist_lock);
+       }
 
        need_forkexit_callback |= ss->fork || ss->exit;
 
@@ -1573,8 +1960,22 @@ static void cgroup_init_subsys(struct cgroup_subsys *ss)
 int __init cgroup_init_early(void)
 {
        int i;
+       kref_init(&init_css_set.ref);
+       kref_get(&init_css_set.ref);
+       INIT_LIST_HEAD(&init_css_set.list);
+       INIT_LIST_HEAD(&init_css_set.cg_links);
+       INIT_LIST_HEAD(&init_css_set.tasks);
+       css_set_count = 1;
        init_cgroup_root(&rootnode);
        list_add(&rootnode.root_list, &roots);
+       root_count = 1;
+       init_task.cgroups = &init_css_set;
+
+       init_css_set_link.cg = &init_css_set;
+       list_add(&init_css_set_link.cont_link_list,
+                &rootnode.top_cgroup.css_sets);
+       list_add(&init_css_set_link.cg_link_list,
+                &init_css_set.cg_links);
 
        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
                struct cgroup_subsys *ss = subsys[i];
@@ -1715,29 +2116,13 @@ static int proc_cgroupstats_show(struct seq_file *m, 
void *v)
        int i;
        struct cgroupfs_root *root;
 
+       seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\n");
        mutex_lock(&cgroup_mutex);
-       seq_puts(m, "Hierarchies:\n");
-       for_each_root(root) {
-               struct cgroup_subsys *ss;
-               int first = 1;
-               seq_printf(m, "%p: bits=%lx cgroups=%d (", root,
-                          root->subsys_bits, root->number_of_cgroups);
-               for_each_subsys(root, ss) {
-                       seq_printf(m, "%s%s", first ? "" : ", ", ss->name);
-                       first = false;
-               }
-               seq_putc(m, ')');
-               if (root->sb) {
-                       seq_printf(m, " s_active=%d",
-                                  atomic_read(&root->sb->s_active));
-               }
-               seq_putc(m, '\n');
-       }
-       seq_puts(m, "Subsystems:\n");
        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
                struct cgroup_subsys *ss = subsys[i];
-               seq_printf(m, "%d: name=%s hierarchy=%p\n",
-                          i, ss->name, ss->root);
+               seq_printf(m, "%s\t%lu\t%d\n",
+                          ss->name, ss->root->subsys_bits,
+                          ss->root->number_of_cgroups);
        }
        mutex_unlock(&cgroup_mutex);
        return 0;
@@ -1765,18 +2150,19 @@ static struct file_operations 
proc_cgroupstats_operations = {
  * fork.c by dup_task_struct().  However, we ignore that copy, since
  * it was not made under the protection of RCU or cgroup_mutex, so
  * might no longer be a valid cgroup pointer.  attach_task() might
- * have already changed current->cgroup, allowing the previously
- * referenced cgroup to be removed and freed.
+ * have already changed current->cgroups, allowing the previously
+ * referenced cgroup group to be removed and freed.
  *
  * At the point that cgroup_fork() is called, 'current' is the parent
  * task, and the passed argument 'child' points to the child task.
  */
 void cgroup_fork(struct task_struct *child)
 {
-       rcu_read_lock();
-       child->cgroups = rcu_dereference(current->cgroups);
-       get_css_set(&child->cgroups);
-       rcu_read_unlock();
+       task_lock(current);
+       child->cgroups = current->cgroups;
+       get_css_set(child->cgroups);
+       task_unlock(current);
+       INIT_LIST_HEAD(&child->cg_list);
 }
 
 /**
@@ -1797,6 +2183,21 @@ void cgroup_fork_callbacks(struct task_struct *child)
 }
 
 /**
+ * cgroup_post_fork - called on a new task after adding it to the
+ * task list. Adds the task to the list running through its css_set
+ * if necessary. Has to be after the task is visible on the task list
+ * in case we race with the first call to cgroup_iter_start() - to
+ * guarantee that the new task ends up on its list. */
+void cgroup_post_fork(struct task_struct *child)
+{
+       if (use_task_css_set_links) {
+               write_lock(&css_set_lock);
+               if (list_empty(&child->cg_list))
+                       list_add(&child->cg_list, &child->cgroups->tasks);
+               write_unlock(&css_set_lock);
+       }
+}
+/**
  * cgroup_exit - detach cgroup from exiting task
  * @tsk: pointer to task_struct of exiting process
  *
@@ -1834,6 +2235,7 @@ void cgroup_fork_callbacks(struct task_struct *child)
 void cgroup_exit(struct task_struct *tsk, int run_callbacks)
 {
        int i;
+       struct css_set *cg;
 
        if (run_callbacks && need_forkexit_callback) {
                for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
@@ -1842,11 +2244,26 @@ void cgroup_exit(struct task_struct *tsk, int 
run_callbacks)
                                ss->exit(ss, tsk);
                }
        }
+
+       /*
+        * Unlink from the css_set task list if necessary.
+        * Optimistically check cg_list before taking
+        * css_set_lock
+        */
+       if (!list_empty(&tsk->cg_list)) {
+               write_lock(&css_set_lock);
+               if (!list_empty(&tsk->cg_list))
+                       list_del(&tsk->cg_list);
+               write_unlock(&css_set_lock);
+       }
+
        /* Reassign the task to the init_css_set. */
        task_lock(tsk);
-       put_css_set(&tsk->cgroups);
-       tsk->cgroups = init_task.cgroups;
+       cg = tsk->cgroups;
+       tsk->cgroups = &init_css_set;
        task_unlock(tsk);
+       if (cg)
+               put_css_set(cg);
 }
 
 /**
@@ -1880,7 +2297,7 @@ int cgroup_clone(struct task_struct *tsk, struct 
cgroup_subsys *subsys)
                mutex_unlock(&cgroup_mutex);
                return 0;
        }
-       cg = &tsk->cgroups;
+       cg = tsk->cgroups;
        parent = task_cgroup(tsk, subsys->subsys_id);
 
        snprintf(nodename, MAX_CGROUP_TYPE_NAMELEN, "node_%d", tsk->pid);
@@ -1888,6 +2305,8 @@ int cgroup_clone(struct task_struct *tsk, struct 
cgroup_subsys *subsys)
        /* Pin the hierarchy */
        atomic_inc(&parent->root->sb->s_active);
 
+       /* Keep the cgroup alive */
+       get_css_set(cg);
        mutex_unlock(&cgroup_mutex);
 
        /* Now do the VFS work to create a cgroup */
@@ -1931,6 +2350,7 @@ int cgroup_clone(struct task_struct *tsk, struct 
cgroup_subsys *subsys)
            (parent != task_cgroup(tsk, subsys->subsys_id))) {
                /* Aargh, we raced ... */
                mutex_unlock(&inode->i_mutex);
+               put_css_set(cg);
 
                deactivate_super(parent->root->sb);
                /* The cgroup is still accessible in the VFS, but
@@ -1954,6 +2374,7 @@ int cgroup_clone(struct task_struct *tsk, struct 
cgroup_subsys *subsys)
 
  out_release:
        mutex_unlock(&inode->i_mutex);
+       put_css_set(cg);
        deactivate_super(parent->root->sb);
        return ret;
 }
diff --git a/kernel/fork.c b/kernel/fork.c
index e7c1814..fcac389 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1301,6 +1301,7 @@ static struct task_struct *copy_process(unsigned long 
clone_flags,
        spin_unlock(&current->sighand->siglock);
        write_unlock_irq(&tasklist_lock);
        proc_fork_connector(p);
+       cgroup_post_fork(p);
        return p;
 
 bad_fork_cleanup_namespaces:
-
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