1 files changed, 199 insertions, 49 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index ccec722213a4..8ba680985335 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -207,6 +207,7 @@ struct cg_cgroup_link {
          * cgroup, anchored on cgroup->css_sets
          */
         struct list_head cgrp_link_list;
+        struct cgroup *cgrp;
         /*
          * List running through cg_cgroup_links pointing at a
          * single css_set object, anchored on css_set->cg_links
@@ -233,8 +234,11 @@ static int cgroup_subsys_init_idr(struct cgroup_subsys *ss);
 static DEFINE_RWLOCK(css_set_lock);
 static int css_set_count;
 
-/* hash table for cgroup groups. This improves the performance to
- * find an existing css_set */
+/*
+ * hash table for cgroup groups. This improves the performance to find
+ * an existing css_set. This hash doesn't (currently) take into
+ * account cgroups in empty hierarchies.
+ */
 #define CSS_SET_HASH_BITS       7
 #define CSS_SET_TABLE_SIZE      (1 << CSS_SET_HASH_BITS)
 static struct hlist_head css_set_table[CSS_SET_TABLE_SIZE];
@@ -344,6 +348,78 @@ static inline void put_css_set_taskexit(struct css_set *cg)
 }
 
 /*
+ * compare_css_sets - helper function for find_existing_css_set().
+ * @cg: candidate css_set being tested
+ * @old_cg: existing css_set for a task
+ * @new_cgrp: cgroup that's being entered by the task
+ * @template: desired set of css pointers in css_set (pre-calculated)
+ *
+ * Returns true if "cg" matches "old_cg" except for the hierarchy
+ * which "new_cgrp" belongs to, for which it should match "new_cgrp".
+ */
+static bool compare_css_sets(struct css_set *cg,
+                             struct css_set *old_cg,
+                             struct cgroup *new_cgrp,
+                             struct cgroup_subsys_state *template[])
+{
+        struct list_head *l1, *l2;
+
+        if (memcmp(template, cg->subsys, sizeof(cg->subsys))) {
+                /* Not all subsystems matched */
+                return false;
+        }
+
+        /*
+         * Compare cgroup pointers in order to distinguish between
+         * different cgroups in heirarchies with no subsystems. We
+         * could get by with just this check alone (and skip the
+         * memcmp above) but on most setups the memcmp check will
+         * avoid the need for this more expensive check on almost all
+         * candidates.
+         */
+
+        l1 = &cg->cg_links;
+        l2 = &old_cg->cg_links;
+        while (1) {
+                struct cg_cgroup_link *cgl1, *cgl2;
+                struct cgroup *cg1, *cg2;
+
+                l1 = l1->next;
+                l2 = l2->next;
+                /* See if we reached the end - both lists are equal length. */
+                if (l1 == &cg->cg_links) {
+                        BUG_ON(l2 != &old_cg->cg_links);
+                        break;
+                } else {
+                        BUG_ON(l2 == &old_cg->cg_links);
+                }
+                /* Locate the cgroups associated with these links. */
+                cgl1 = list_entry(l1, struct cg_cgroup_link, cg_link_list);
+                cgl2 = list_entry(l2, struct cg_cgroup_link, cg_link_list);
+                cg1 = cgl1->cgrp;
+                cg2 = cgl2->cgrp;
+                /* Hierarchies should be linked in the same order. */
+                BUG_ON(cg1->root != cg2->root);
+
+                /*
+                 * If this hierarchy is the hierarchy of the cgroup
+                 * that's changing, then we need to check that this
+                 * css_set points to the new cgroup; if it's any other
+                 * hierarchy, then this css_set should point to the
+                 * same cgroup as the old css_set.
+                 */
+                if (cg1->root == new_cgrp->root) {
+                        if (cg1 != new_cgrp)
+                                return false;
+                } else {
+                        if (cg1 != cg2)
+                                return false;
+                }
+        }
+        return true;
+}
+
+/*
  * find_existing_css_set() is a helper for
  * find_css_set(), and checks to see whether an existing
  * css_set is suitable.
@@ -384,10 +460,11 @@ static struct css_set *find_existing_css_set(
 
         hhead = css_set_hash(template);
         hlist_for_each_entry(cg, node, hhead, hlist) {
-                if (!memcmp(template, cg->subsys, sizeof(cg->subsys))) {
-                        /* All subsystems matched */
-                        return cg;
-                }
+                if (!compare_css_sets(cg, oldcg, cgrp, template))
+                        continue;
+
+                /* This css_set matches what we need */
+                return cg;
         }
 
         /* No existing cgroup group matched */
@@ -441,8 +518,13 @@ static void link_css_set(struct list_head *tmp_cg_links,
         link = list_first_entry(tmp_cg_links, struct cg_cgroup_link,
                                 cgrp_link_list);
         link->cg = cg;
+        link->cgrp = cgrp;
         list_move(&link->cgrp_link_list, &cgrp->css_sets);
-        list_add(&link->cg_link_list, &cg->cg_links);
+        /*
+         * Always add links to the tail of the list so that the list
+         * is sorted by order of hierarchy creation
+         */
+        list_add_tail(&link->cg_link_list, &cg->cg_links);
 }
 
 /*
@@ -462,6 +544,7 @@ static struct css_set *find_css_set(
         struct list_head tmp_cg_links;
 
         struct hlist_head *hhead;
+        struct cg_cgroup_link *link;
 
         /* First see if we already have a cgroup group that matches
          * the desired set */
@@ -497,18 +580,14 @@ static struct css_set *find_css_set(
         /* Add reference counts and links from the new css_set. */
         for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
                 struct cgroup *cgrp = res->subsys[i]->cgroup;
-                struct cgroup_subsys *ss = subsys[i];
                 atomic_inc(&cgrp->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)
-                        link_css_set(&tmp_cg_links, res, cgrp);
         }
-        if (list_empty(&rootnode.subsys_list))
-                link_css_set(&tmp_cg_links, res, dummytop);
+        list_for_each_entry(link, &oldcg->cg_links, cg_link_list) {
+                struct cgroup *c = link->cgrp;
+                if (c->root == cgrp->root)
+                        c = cgrp;
+                link_css_set(&tmp_cg_links, res, c);
+        }
 
         BUG_ON(!list_empty(&tmp_cg_links));
 
@@ -524,6 +603,41 @@ static struct css_set *find_css_set(
 }
 
 /*
+ * Return the cgroup for "task" from the given hierarchy. Must be
+ * called with cgroup_mutex held.
+ */
+static struct cgroup *task_cgroup_from_root(struct task_struct *task,
+                                            struct cgroupfs_root *root)
+{
+        struct css_set *css;
+        struct cgroup *res = NULL;
+
+        BUG_ON(!mutex_is_locked(&cgroup_mutex));
+        read_lock(&css_set_lock);
+        /*
+         * No need to lock the task - since we hold cgroup_mutex the
+         * task can't change groups, so the only thing that can happen
+         * is that it exits and its css is set back to init_css_set.
+         */
+        css = task->cgroups;
+        if (css == &init_css_set) {
+                res = &root->top_cgroup;
+        } else {
+                struct cg_cgroup_link *link;
+                list_for_each_entry(link, &css->cg_links, cg_link_list) {
+                        struct cgroup *c = link->cgrp;
+                        if (c->root == root) {
+                                res = c;
+                                break;
+                        }
+                }
+        }
+        read_unlock(&css_set_lock);
+        BUG_ON(!res);
+        return res;
+}
+
+/*
  * There is one global cgroup mutex. We also require taking
  * task_lock() when dereferencing a task's cgroup subsys pointers.
  * See "The task_lock() exception", at the end of this comment.
@@ -1361,27 +1475,6 @@ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
         return 0;
 }
 
-/*
- * Return the first subsystem attached to a cgroup's hierarchy, and
- * its subsystem id.
- */
-
-static void get_first_subsys(const struct cgroup *cgrp,
-                        struct cgroup_subsys_state **css, int *subsys_id)
-{
-        const struct cgroupfs_root *root = cgrp->root;
-        const struct cgroup_subsys *test_ss;
-        BUG_ON(list_empty(&root->subsys_list));
-        test_ss = list_entry(root->subsys_list.next,
-                             struct cgroup_subsys, sibling);
-        if (css) {
-                *css = cgrp->subsys[test_ss->subsys_id];
-                BUG_ON(!*css);
-        }
-        if (subsys_id)
-                *subsys_id = test_ss->subsys_id;
-}
-
 /**
  * cgroup_attach_task - attach task 'tsk' to cgroup 'cgrp'
  * @cgrp: the cgroup the task is attaching to
@@ -1398,12 +1491,9 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
         struct css_set *cg;
         struct css_set *newcg;
         struct cgroupfs_root *root = cgrp->root;
-        int subsys_id;
-
-        get_first_subsys(cgrp, NULL, &subsys_id);
 
         /* Nothing to do if the task is already in that cgroup */
-        oldcgrp = task_cgroup(tsk, subsys_id);
+        oldcgrp = task_cgroup_from_root(tsk, root);
         if (cgrp == oldcgrp)
                 return 0;
 
@@ -1961,7 +2051,7 @@ int cgroup_task_count(const struct cgroup *cgrp)
  * the start of a css_set
  */
 static void cgroup_advance_iter(struct cgroup *cgrp,
-                                          struct cgroup_iter *it)
+                                struct cgroup_iter *it)
 {
         struct list_head *l = it->cg_link;
         struct cg_cgroup_link *link;
@@ -2964,6 +3054,7 @@ int __init cgroup_init_early(void)
         init_task.cgroups = &init_css_set;
 
         init_css_set_link.cg = &init_css_set;
+        init_css_set_link.cgrp = dummytop;
         list_add(&init_css_set_link.cgrp_link_list,
                  &rootnode.top_cgroup.css_sets);
         list_add(&init_css_set_link.cg_link_list,
@@ -3071,7 +3162,6 @@ static int proc_cgroup_show(struct seq_file *m, void *v)
         for_each_active_root(root) {
                 struct cgroup_subsys *ss;
                 struct cgroup *cgrp;
-                int subsys_id;
                 int count = 0;
 
                 seq_printf(m, "%lu:", root->subsys_bits);
@@ -3081,8 +3171,7 @@ static int proc_cgroup_show(struct seq_file *m, void *v)
                         seq_printf(m, "%sname=%s", count ? "," : "",
                                    root->name);
                 seq_putc(m, ':');
-                get_first_subsys(&root->top_cgroup, NULL, &subsys_id);
-                cgrp = task_cgroup(tsk, subsys_id);
+                cgrp = task_cgroup_from_root(tsk, root);
                 retval = cgroup_path(cgrp, buf, PAGE_SIZE);
                 if (retval < 0)
                         goto out_unlock;
@@ -3408,13 +3497,11 @@ int cgroup_is_descendant(const struct cgroup *cgrp, struct task_struct *task)
 {
         int ret;
         struct cgroup *target;
-        int subsys_id;
 
         if (cgrp == dummytop)
                 return 1;
 
-        get_first_subsys(cgrp, NULL, &subsys_id);
-        target = task_cgroup(task, subsys_id);
+        target = task_cgroup_from_root(task, cgrp->root);
         while (cgrp != target && cgrp!= cgrp->top_cgroup)
                 cgrp = cgrp->parent;
         ret = (cgrp == target);
@@ -3824,6 +3911,59 @@ static u64 current_css_set_refcount_read(struct cgroup *cont,
         return count;
 }
 
+static int current_css_set_cg_links_read(struct cgroup *cont,
+                                         struct cftype *cft,
+                                         struct seq_file *seq)
+{
+        struct cg_cgroup_link *link;
+        struct css_set *cg;
+
+        read_lock(&css_set_lock);
+        rcu_read_lock();
+        cg = rcu_dereference(current->cgroups);
+        list_for_each_entry(link, &cg->cg_links, cg_link_list) {
+                struct cgroup *c = link->cgrp;
+                const char *name;
+
+                if (c->dentry)
+                        name = c->dentry->d_name.name;
+                else
+                        name = "?";
+                seq_printf(seq, "Root %lu group %s\n",
+                           c->root->subsys_bits, name);
+        }
+        rcu_read_unlock();
+        read_unlock(&css_set_lock);
+        return 0;
+}
+
+#define MAX_TASKS_SHOWN_PER_CSS 25
+static int cgroup_css_links_read(struct cgroup *cont,
+                                 struct cftype *cft,
+                                 struct seq_file *seq)
+{
+        struct cg_cgroup_link *link;
+
+        read_lock(&css_set_lock);
+        list_for_each_entry(link, &cont->css_sets, cgrp_link_list) {
+                struct css_set *cg = link->cg;
+                struct task_struct *task;
+                int count = 0;
+                seq_printf(seq, "css_set %p\n", cg);
+                list_for_each_entry(task, &cg->tasks, cg_list) {
+                        if (count++ > MAX_TASKS_SHOWN_PER_CSS) {
+                                seq_puts(seq, "  ...\n");
+                                break;
+                        } else {
+                                seq_printf(seq, "  task %d\n",
+                                           task_pid_vnr(task));
+                        }
+                }
+        }
+        read_unlock(&css_set_lock);
+        return 0;
+}
+
 static u64 releasable_read(struct cgroup *cgrp, struct cftype *cft)
 {
         return test_bit(CGRP_RELEASABLE, &cgrp->flags);
@@ -3850,6 +3990,16 @@ static struct cftype debug_files[] =  {
         },
 
         {
+                .name = "current_css_set_cg_links",
+                .read_seq_string = current_css_set_cg_links_read,
+        },
+
+        {
+                .name = "cgroup_css_links",
+                .read_seq_string = cgroup_css_links_read,
+        },
+
+        {
                 .name = "releasable",
                 .read_u64 = releasable_read,
         },