3 files changed, 1 insertions, 95 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index a3098046250b..47868a86ba2b 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -145,10 +145,6 @@ enum {
         /* Control Group requires release notifications to userspace */
         CGRP_NOTIFY_ON_RELEASE,
         /*
-         * A thread in rmdir() is wating for this cgroup.
-         */
-        CGRP_WAIT_ON_RMDIR,
-        /*
          * Clone cgroup values when creating a new child cgroup
          */
         CGRP_CLONE_CHILDREN,
@@ -412,23 +408,6 @@ int cgroup_task_count(const struct cgroup *cgrp);
 int cgroup_is_descendant(const struct cgroup *cgrp, struct task_struct *task);
 
 /*
- * When the subsys has to access css and may add permanent refcnt to css,
- * it should take care of racy conditions with rmdir(). Following set of
- * functions, is for stop/restart rmdir if necessary.
- * Because these will call css_get/put, "css" should be alive css.
- *
- *  cgroup_exclude_rmdir();
- *  ...do some jobs which may access arbitrary empty cgroup
- *  cgroup_release_and_wakeup_rmdir();
- *
- *  When someone removes a cgroup while cgroup_exclude_rmdir() holds it,
- *  it sleeps and cgroup_release_and_wakeup_rmdir() will wake him up.
- */
-
-void cgroup_exclude_rmdir(struct cgroup_subsys_state *css);
-void cgroup_release_and_wakeup_rmdir(struct cgroup_subsys_state *css);
-
-/*
  * Control Group taskset, used to pass around set of tasks to cgroup_subsys
  * methods.
  */
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 66204a6f68f3..c5f6fb28dd0e 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -966,33 +966,6 @@ static void cgroup_d_remove_dir(struct dentry *dentry)
 }
 
 /*
- * A queue for waiters to do rmdir() cgroup. A tasks will sleep when
- * cgroup->count == 0 && list_empty(&cgroup->children) && subsys has some
- * reference to css->refcnt. In general, this refcnt is expected to goes down
- * to zero, soon.
- *
- * CGRP_WAIT_ON_RMDIR flag is set under cgroup's inode->i_mutex;
- */
-static DECLARE_WAIT_QUEUE_HEAD(cgroup_rmdir_waitq);
-
-static void cgroup_wakeup_rmdir_waiter(struct cgroup *cgrp)
-{
-        if (unlikely(test_and_clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags)))
-                wake_up_all(&cgroup_rmdir_waitq);
-}
-
-void cgroup_exclude_rmdir(struct cgroup_subsys_state *css)
-{
-        css_get(css);
-}
-
-void cgroup_release_and_wakeup_rmdir(struct cgroup_subsys_state *css)
-{
-        cgroup_wakeup_rmdir_waiter(css->cgroup);
-        css_put(css);
-}
-
-/*
  * Call with cgroup_mutex held. Drops reference counts on modules, including
  * any duplicate ones that parse_cgroupfs_options took. If this function
  * returns an error, no reference counts are touched.
@@ -1963,12 +1936,6 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
         }
 
         synchronize_rcu();
-
-        /*
-         * wake up rmdir() waiter. the rmdir should fail since the cgroup
-         * is no longer empty.
-         */
-        cgroup_wakeup_rmdir_waiter(cgrp);
 out:
         if (retval) {
                 for_each_subsys(root, ss) {
@@ -2138,7 +2105,6 @@ static int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
          * step 5: success! and cleanup
          */
         synchronize_rcu();
-        cgroup_wakeup_rmdir_waiter(cgrp);
         retval = 0;
 out_put_css_set_refs:
         if (retval) {
@@ -4058,26 +4024,13 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
         struct cgroup_event *event, *tmp;
         struct cgroup_subsys *ss;
 
-        /*
-         * In general, subsystem has no css->refcnt after pre_destroy(). But
-         * in racy cases, subsystem may have to get css->refcnt after
-         * pre_destroy() and it makes rmdir return with -EBUSY. This sometimes
-         * make rmdir return -EBUSY too often. To avoid that, we use waitqueue
-         * for cgroup's rmdir. CGRP_WAIT_ON_RMDIR is for synchronizing rmdir
-         * and subsystem's reference count handling. Please see css_get/put
-         * and css_tryget() and cgroup_wakeup_rmdir_waiter() implementation.
-         */
-        set_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
-
         /* the vfs holds both inode->i_mutex already */
         mutex_lock(&cgroup_mutex);
         parent = cgrp->parent;
         if (atomic_read(&cgrp->count) || !list_empty(&cgrp->children)) {
-                clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
                 mutex_unlock(&cgroup_mutex);
                 return -EBUSY;
         }
-        prepare_to_wait(&cgroup_rmdir_waitq, &wait, TASK_INTERRUPTIBLE);
 
         /*
          * Block new css_tryget() by deactivating refcnt and mark @cgrp
@@ -4114,9 +4067,6 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
         for_each_subsys(cgrp->root, ss)
                 css_put(cgrp->subsys[ss->subsys_id]);
 
-        finish_wait(&cgroup_rmdir_waitq, &wait);
-        clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
-
         raw_spin_lock(&release_list_lock);
         if (!list_empty(&cgrp->release_list))
                 list_del_init(&cgrp->release_list);
@@ -4864,7 +4814,6 @@ void __css_put(struct cgroup_subsys_state *css)
                         set_bit(CGRP_RELEASABLE, &cgrp->flags);
                         check_for_release(cgrp);
                 }
-                cgroup_wakeup_rmdir_waiter(cgrp);
                 break;
         case 0:
                 schedule_work(&css->dput_work);
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 37c356646544..930edfaa5187 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2681,13 +2681,6 @@ static int mem_cgroup_move_account(struct page *page,
         /* caller should have done css_get */
         pc->mem_cgroup = to;
         mem_cgroup_charge_statistics(to, anon, nr_pages);
-        /*
-         * We charges against "to" which may not have any tasks. Then, "to"
-         * can be under rmdir(). But in current implementation, caller of
-         * this function is just force_empty() and move charge, so it's
-         * guaranteed that "to" is never removed. So, we don't check rmdir
-         * status here.
-         */
         move_unlock_mem_cgroup(from, &flags);
         ret = 0;
 unlock:
@@ -2893,7 +2886,6 @@ __mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *memcg,
                 return;
         if (!memcg)
                 return;
-        cgroup_exclude_rmdir(&memcg->css);
 
         __mem_cgroup_commit_charge(memcg, page, 1, ctype, true);
         /*
@@ -2907,12 +2899,6 @@ __mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *memcg,
                 swp_entry_t ent = {.val = page_private(page)};
                 mem_cgroup_uncharge_swap(ent);
         }
-        /*
-         * At swapin, we may charge account against cgroup which has no tasks.
-         * So, rmdir()->pre_destroy() can be called while we do this charge.
-         * In that case, we need to call pre_destroy() again. check it here.
-         */
-        cgroup_release_and_wakeup_rmdir(&memcg->css);
 }
 
 void mem_cgroup_commit_charge_swapin(struct page *page,
@@ -3360,8 +3346,7 @@ void mem_cgroup_end_migration(struct mem_cgroup *memcg,
 
         if (!memcg)
                 return;
-        /* blocks rmdir() */
-        cgroup_exclude_rmdir(&memcg->css);
+
         if (!migration_ok) {
                 used = oldpage;
                 unused = newpage;
@@ -3395,13 +3380,6 @@ void mem_cgroup_end_migration(struct mem_cgroup *memcg,
          */
         if (anon)
                 mem_cgroup_uncharge_page(used);
-        /*
-         * At migration, we may charge account against cgroup which has no
-         * tasks.
-         * So, rmdir()->pre_destroy() can be called while we do this charge.
-         * In that case, we need to call pre_destroy() again. check it here.
-         */
-        cgroup_release_and_wakeup_rmdir(&memcg->css);
 }
 
 /*