cgroup: enable task_cg_lists on the first cgroup mount

[firefly-linux-kernel-4.4.55.git] / kernel / cgroup.c

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 878cd1810ad1bd31031b3d0fcc801513b3f4f3ef..506f6da67ad1c0e1361db63d11c0ecd91e340802 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -173,6 +173,7 @@ static int cgroup_destroy_locked(struct cgroup *cgrp);
 static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
                              bool is_add);
 static void cgroup_pidlist_destroy_all(struct cgroup *cgrp);
+static void cgroup_enable_task_cg_lists(void);
 
 /**
  * cgroup_css - obtain a cgroup's css for the specified subsystem
@@ -375,7 +376,7 @@ static unsigned long css_set_hash(struct cgroup_subsys_state *css[])
  * fork()/exit() overhead for people who have cgroups compiled into their
  * kernel but not actually in use.
  */
-static int use_task_css_set_links __read_mostly;
+static bool use_task_css_set_links __read_mostly;
 
 static void __put_css_set(struct css_set *cset, int taskexit)
 {
@@ -1441,6 +1442,13 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
        struct cgroup_sb_opts opts;
        struct dentry *dentry;
        int ret;
+
+       /*
+        * The first time anyone tries to mount a cgroup, enable the list
+        * linking each css_set to its tasks and fix up all existing tasks.
+        */
+       if (!use_task_css_set_links)
+               cgroup_enable_task_cg_lists();
 retry:
        mutex_lock(&cgroup_tree_mutex);
        mutex_lock(&cgroup_mutex);
@@ -1692,10 +1700,8 @@ static void cgroup_task_migrate(struct cgroup *old_cgrp,
        rcu_assign_pointer(tsk->cgroups, new_cset);
        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_move(&tsk->cg_list, &new_cset->tasks);
+       list_move(&tsk->cg_list, &new_cset->tasks);
        write_unlock(&css_set_lock);
 
        /*
@@ -2362,13 +2368,19 @@ int cgroup_task_count(const struct cgroup *cgrp)
  * To reduce the fork() overhead for systems that are not actually using
  * their cgroups capability, we don't maintain the lists running through
  * each css_set to its tasks until we see the list actually used - in other
- * words after the first call to css_task_iter_start().
+ * words after the first mount.
  */
 static void cgroup_enable_task_cg_lists(void)
 {
        struct task_struct *p, *g;
+
        write_lock(&css_set_lock);
-       use_task_css_set_links = 1;
+
+       if (use_task_css_set_links)
+               goto out_unlock;
+
+       use_task_css_set_links = true;
+
        /*
         * We need tasklist_lock because RCU is not safe against
         * while_each_thread(). Besides, a forking task that has passed
@@ -2379,16 +2391,22 @@ static void cgroup_enable_task_cg_lists(void)
        read_lock(&tasklist_lock);
        do_each_thread(g, p) {
                task_lock(p);
+
+               WARN_ON_ONCE(!list_empty(&p->cg_list) ||
+                            task_css_set(p) != &init_css_set);
+
                /*
                 * We should check if the process is exiting, otherwise
                 * it will race with cgroup_exit() in that the list
                 * entry won't be deleted though the process has exited.
                 */
-               if (!(p->flags & PF_EXITING) && list_empty(&p->cg_list))
+               if (!(p->flags & PF_EXITING))
                        list_add(&p->cg_list, &task_css_set(p)->tasks);
+
                task_unlock(p);
        } while_each_thread(g, p);
        read_unlock(&tasklist_lock);
+out_unlock:
        write_unlock(&css_set_lock);
 }
 
@@ -2621,13 +2639,8 @@ void css_task_iter_start(struct cgroup_subsys_state *css,
                         struct css_task_iter *it)
        __acquires(css_set_lock)
 {
-       /*
-        * The first time anyone tries to iterate across a css, 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)
-               cgroup_enable_task_cg_lists();
+       /* no one should try to iterate before mounting cgroups */
+       WARN_ON_ONCE(!use_task_css_set_links);
 
        read_lock(&css_set_lock);