5 files changed, 156 insertions, 336 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index cafcd7431189..6ce36ff98a41 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -600,7 +600,7 @@ struct cftype blkcg_files[] = {
  *
  * This is the blkcg counterpart of ioc_release_fn().
  */
-static int blkcg_pre_destroy(struct cgroup *cgroup)
+static void blkcg_pre_destroy(struct cgroup *cgroup)
 {
         struct blkcg *blkcg = cgroup_to_blkcg(cgroup);
 
@@ -622,7 +622,6 @@ static int blkcg_pre_destroy(struct cgroup *cgroup)
         }
 
         spin_unlock_irq(&blkcg->lock);
-        return 0;
 }
 
 static void blkcg_destroy(struct cgroup *cgroup)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 4cd1d0fd2542..fe876a77031a 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -81,8 +81,6 @@ struct cgroup_subsys_state {
 /* bits in struct cgroup_subsys_state flags field */
 enum {
         CSS_ROOT, /* This CSS is the root of the subsystem */
-        CSS_REMOVED, /* This CSS is dead */
-        CSS_CLEAR_CSS_REFS,             /* @ss->__DEPRECATED_clear_css_refs */
 };
 
 /* Caller must verify that the css is not for root cgroup */
@@ -105,11 +103,6 @@ static inline void css_get(struct cgroup_subsys_state *css)
                 __css_get(css, 1);
 }
 
-static inline bool css_is_removed(struct cgroup_subsys_state *css)
-{
-        return test_bit(CSS_REMOVED, &css->flags);
-}
-
 /*
  * Call css_tryget() to take a reference on a css if your existing
  * (known-valid) reference isn't already ref-counted. Returns false if
@@ -148,10 +141,6 @@ 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,
@@ -421,23 +410,6 @@ 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.
  */
@@ -466,7 +438,7 @@ int cgroup_taskset_size(struct cgroup_taskset *tset);
 
 struct cgroup_subsys {
         struct cgroup_subsys_state *(*create)(struct cgroup *cgrp);
-        int (*pre_destroy)(struct cgroup *cgrp);
+        void (*pre_destroy)(struct cgroup *cgrp);
         void (*destroy)(struct cgroup *cgrp);
         int (*can_attach)(struct cgroup *cgrp, struct cgroup_taskset *tset);
         void (*cancel_attach)(struct cgroup *cgrp, struct cgroup_taskset *tset);
@@ -488,17 +460,6 @@ struct cgroup_subsys {
         bool use_id;
 
         /*
-         * If %true, cgroup removal will try to clear css refs by retrying
-         * ss->pre_destroy() until there's no css ref left.  This behavior
-         * is strictly for backward compatibility and will be removed as
-         * soon as the current user (memcg) is updated.
-         *
-         * If %false, ss->pre_destroy() can't fail and cgroup removal won't
-         * wait for css refs to drop to zero before proceeding.
-         */
-        bool __DEPRECATED_clear_css_refs;
-
-        /*
          * If %false, this subsystem is properly hierarchical -
          * configuration, resource accounting and restriction on a parent
          * cgroup cover those of its children.  If %true, hierarchy support
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index b7a0171067ea..e3045ad4267a 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -171,8 +171,8 @@ 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.
+         * is called after synchronize_rcu(). But for safe use, css_tryget()
+         * should be used for avoiding race.
          */
         struct cgroup_subsys_state __rcu *css;
         /*
@@ -854,30 +854,6 @@ static struct inode *cgroup_new_inode(umode_t mode, struct super_block *sb)
         return inode;
 }
 
-/*
- * Call subsys's pre_destroy handler.
- * This is called before css refcnt check.
- */
-static int cgroup_call_pre_destroy(struct cgroup *cgrp)
-{
-        struct cgroup_subsys *ss;
-        int ret = 0;
-
-        for_each_subsys(cgrp->root, ss) {
-                if (!ss->pre_destroy)
-                        continue;
-
-                ret = ss->pre_destroy(cgrp);
-                if (ret) {
-                        /* ->pre_destroy() failure is being deprecated */
-                        WARN_ON_ONCE(!ss->__DEPRECATED_clear_css_refs);
-                        break;
-                }
-        }
-
-        return ret;
-}
-
 static void cgroup_diput(struct dentry *dentry, struct inode *inode)
 {
         /* is dentry a directory ? if so, kfree() associated cgroup */
@@ -1015,33 +991,6 @@ 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.
@@ -2026,12 +1975,6 @@ 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) {
@@ -2201,7 +2144,6 @@ 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) {
@@ -4023,14 +3965,12 @@ static void init_cgroup_css(struct cgroup_subsys_state *css,
         cgrp->subsys[ss->subsys_id] = css;
 
         /*
-         * If !clear_css_refs, css holds an extra ref to @cgrp->dentry
-         * which is put on the last css_put().  dput() requires process
-         * context, which css_put() may be called without.  @css->dput_work
-         * will be used to invoke dput() asynchronously from css_put().
+         * css holds an extra ref to @cgrp->dentry which is put on the last
+         * css_put().  dput() requires process context, which css_put() may
+         * be called without.  @css->dput_work will be used to invoke
+         * dput() asynchronously from css_put().
          */
         INIT_WORK(&css->dput_work, css_dput_fn);
-        if (ss->__DEPRECATED_clear_css_refs)
-                set_bit(CSS_CLEAR_CSS_REFS, &css->flags);
 }
 
 /*
@@ -4054,6 +3994,18 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
         if (!cgrp)
                 return -ENOMEM;
 
+        /*
+         * Only live parents can have children.  Note that the liveliness
+         * check isn't strictly necessary because cgroup_mkdir() and
+         * cgroup_rmdir() are fully synchronized by i_mutex; however, do it
+         * anyway so that locking is contained inside cgroup proper and we
+         * don't get nasty surprises if we ever grow another caller.
+         */
+        if (!cgroup_lock_live_group(parent)) {
+                err = -ENODEV;
+                goto err_free;
+        }
+
         /* Grab a reference on the superblock so the hierarchy doesn't
          * get deleted on unmount if there are child cgroups.  This
          * can be done outside cgroup_mutex, since the sb can't
@@ -4061,8 +4013,6 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
          * fs */
         atomic_inc(&sb->s_active);
 
-        mutex_lock(&cgroup_mutex);
-
         init_cgroup_housekeeping(cgrp);
 
         cgrp->parent = parent;
@@ -4110,10 +4060,9 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
         if (err < 0)
                 goto err_remove;
 
-        /* If !clear_css_refs, each css holds a ref to the cgroup's dentry */
+        /* each css holds a ref to the cgroup's dentry */
         for_each_subsys(root, ss)
-                if (!ss->__DEPRECATED_clear_css_refs)
-                        dget(dentry);
+                dget(dentry);
 
         /* The cgroup directory was pre-locked for us */
         BUG_ON(!mutex_is_locked(&cgrp->dentry->d_inode->i_mutex));
@@ -4144,7 +4093,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
 
         /* Release the reference count that we took on the superblock */
         deactivate_super(sb);
-
+err_free:
         kfree(cgrp);
         return err;
 }
@@ -4198,71 +4147,6 @@ static int cgroup_has_css_refs(struct cgroup *cgrp)
         return 0;
 }
 
-/*
- * Atomically mark all (or else none) of the cgroup's CSS objects as
- * CSS_REMOVED. Return true on success, or false if the cgroup has
- * busy subsystems. Call with cgroup_mutex held
- *
- * Depending on whether a subsys has __DEPRECATED_clear_css_refs set or
- * not, cgroup removal behaves differently.
- *
- * If clear is set, css refcnt for the subsystem should be zero before
- * cgroup removal can be committed.  This is implemented by
- * CGRP_WAIT_ON_RMDIR and retry logic around ->pre_destroy(), which may be
- * called multiple times until all css refcnts reach zero and is allowed to
- * veto removal on any invocation.  This behavior is deprecated and will be
- * removed as soon as the existing user (memcg) is updated.
- *
- * If clear is not set, each css holds an extra reference to the cgroup's
- * dentry and cgroup removal proceeds regardless of css refs.
- * ->pre_destroy() will be called at least once and is not allowed to fail.
- * On the last put of each css, whenever that may be, the extra dentry ref
- * is put so that dentry destruction happens only after all css's are
- * released.
- */
-static int cgroup_clear_css_refs(struct cgroup *cgrp)
-{
-        struct cgroup_subsys *ss;
-        unsigned long flags;
-        bool failed = false;
-
-        local_irq_save(flags);
-
-        /*
-         * Block new css_tryget() by deactivating refcnt.  If all refcnts
-         * for subsystems w/ clear_css_refs set were 1 at the moment of
-         * deactivation, we succeeded.
-         */
-        for_each_subsys(cgrp->root, ss) {
-                struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
-
-                WARN_ON(atomic_read(&css->refcnt) < 0);
-                atomic_add(CSS_DEACT_BIAS, &css->refcnt);
-
-                if (ss->__DEPRECATED_clear_css_refs)
-                        failed |= css_refcnt(css) != 1;
-        }
-
-        /*
-         * If succeeded, set REMOVED and put all the base refs; otherwise,
-         * restore refcnts to positive values.  Either way, all in-progress
-         * css_tryget() will be released.
-         */
-        for_each_subsys(cgrp->root, ss) {
-                struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
-
-                if (!failed) {
-                        set_bit(CSS_REMOVED, &css->flags);
-                        css_put(css);
-                } else {
-                        atomic_sub(CSS_DEACT_BIAS, &css->refcnt);
-                }
-        }
-
-        local_irq_restore(flags);
-        return !failed;
-}
-
 static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
 {
         struct cgroup *cgrp = dentry->d_fsdata;
@@ -4270,70 +4154,52 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
         struct cgroup *parent;
         DEFINE_WAIT(wait);
         struct cgroup_event *event, *tmp;
-        int ret;
+        struct cgroup_subsys *ss;
 
         /* the vfs holds both inode->i_mutex already */
-again:
         mutex_lock(&cgroup_mutex);
-        if (atomic_read(&cgrp->count) != 0) {
-                mutex_unlock(&cgroup_mutex);
-                return -EBUSY;
-        }
-        if (!list_empty(&cgrp->children)) {
+        parent = cgrp->parent;
+        if (atomic_read(&cgrp->count) || !list_empty(&cgrp->children)) {
                 mutex_unlock(&cgroup_mutex);
                 return -EBUSY;
         }
-        mutex_unlock(&cgroup_mutex);
 
         /*
-         * 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.
+         * Block new css_tryget() by deactivating refcnt and mark @cgrp
+         * removed.  This makes future css_tryget() and child creation
+         * attempts fail thus maintaining the removal conditions verified
+         * above.
          */
-        set_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
+        for_each_subsys(cgrp->root, ss) {
+                struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
 
-        /*
-         * Call pre_destroy handlers of subsys. Notify subsystems
-         * that rmdir() request comes.
-         */
-        ret = cgroup_call_pre_destroy(cgrp);
-        if (ret) {
-                clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
-                return ret;
+                WARN_ON(atomic_read(&css->refcnt) < 0);
+                atomic_add(CSS_DEACT_BIAS, &css->refcnt);
         }
+        set_bit(CGRP_REMOVED, &cgrp->flags);
 
+        /*
+         * Tell subsystems to initate destruction.  pre_destroy() should be
+         * called with cgroup_mutex unlocked.  See 3fa59dfbc3 ("cgroup: fix
+         * potential deadlock in pre_destroy") for details.
+         */
+        mutex_unlock(&cgroup_mutex);
+        for_each_subsys(cgrp->root, ss)
+                if (ss->pre_destroy)
+                        ss->pre_destroy(cgrp);
         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);
-        if (!cgroup_clear_css_refs(cgrp)) {
-                mutex_unlock(&cgroup_mutex);
-                /*
-                 * Because someone may call cgroup_wakeup_rmdir_waiter() before
-                 * prepare_to_wait(), we need to check this flag.
-                 */
-                if (test_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags))
-                        schedule();
-                finish_wait(&cgroup_rmdir_waitq, &wait);
-                clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
-                if (signal_pending(current))
-                        return -EINTR;
-                goto again;
-        }
-        /* NO css_tryget() can success after here. */
-        finish_wait(&cgroup_rmdir_waitq, &wait);
-        clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
+
+        /*
+         * Put all the base refs.  Each css holds an extra reference to the
+         * cgroup's dentry and cgroup removal proceeds regardless of css
+         * refs.  On the last put of each css, whenever that may be, the
+         * extra dentry ref is put so that dentry destruction happens only
+         * after all css's are released.
+         */
+        for_each_subsys(cgrp->root, ss)
+                css_put(cgrp->subsys[ss->subsys_id]);
 
         raw_spin_lock(&release_list_lock);
-        set_bit(CGRP_REMOVED, &cgrp->flags);
         if (!list_empty(&cgrp->release_list))
                 list_del_init(&cgrp->release_list);
         raw_spin_unlock(&release_list_lock);
@@ -5041,15 +4907,17 @@ static void check_for_release(struct cgroup *cgrp)
 /* Caller must verify that the css is not for root cgroup */
 bool __css_tryget(struct cgroup_subsys_state *css)
 {
-        do {
-                int v = css_refcnt(css);
+        while (true) {
+                int t, v;
 
-                if (atomic_cmpxchg(&css->refcnt, v, v + 1) == v)
+                v = css_refcnt(css);
+                t = atomic_cmpxchg(&css->refcnt, v, v + 1);
+                if (likely(t == v))
                         return true;
+                else if (t < 0)
+                        return false;
                 cpu_relax();
-        } while (!test_bit(CSS_REMOVED, &css->flags));
-
-        return false;
+        }
 }
 EXPORT_SYMBOL_GPL(__css_tryget);
 
@@ -5068,11 +4936,9 @@ 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:
-                if (!test_bit(CSS_CLEAR_CSS_REFS, &css->flags))
-                        schedule_work(&css->dput_work);
+                schedule_work(&css->dput_work);
                 break;
         }
         rcu_read_unlock();
diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
index a3f358fb8a0c..0d3a1a317731 100644
--- a/mm/hugetlb_cgroup.c
+++ b/mm/hugetlb_cgroup.c
@@ -155,18 +155,13 @@ out:
  * Force the hugetlb cgroup to empty the hugetlb resources by moving them to
  * the parent cgroup.
  */
-static int hugetlb_cgroup_pre_destroy(struct cgroup *cgroup)
+static void hugetlb_cgroup_pre_destroy(struct cgroup *cgroup)
 {
         struct hstate *h;
         struct page *page;
-        int ret = 0, idx = 0;
+        int idx = 0;
 
         do {
-                if (cgroup_task_count(cgroup) ||
-                    !list_empty(&cgroup->children)) {
-                        ret = -EBUSY;
-                        goto out;
-                }
                 for_each_hstate(h) {
                         spin_lock(&hugetlb_lock);
                         list_for_each_entry(page, &h->hugepage_activelist, lru)
@@ -177,8 +172,6 @@ static int hugetlb_cgroup_pre_destroy(struct cgroup *cgroup)
                 }
                 cond_resched();
         } while (hugetlb_cgroup_have_usage(cgroup));
-out:
-        return ret;
 }
 
 int hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages,
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7acf43bf04a2..08adaaae6fcc 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2337,7 +2337,6 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
 again:
         if (*ptr) { /* css should be a valid one */
                 memcg = *ptr;
-                VM_BUG_ON(css_is_removed(&memcg->css));
                 if (mem_cgroup_is_root(memcg))
                         goto done;
                 if (nr_pages == 1 && consume_stock(memcg))
@@ -2477,9 +2476,9 @@ static void __mem_cgroup_cancel_local_charge(struct mem_cgroup *memcg,
 
 /*
  * A helper function to get mem_cgroup from ID. must be called under
- * rcu_read_lock(). The caller must check css_is_removed() or some if
- * it's concern. (dropping refcnt from swap can be called against removed
- * memcg.)
+ * rcu_read_lock().  The caller is responsible for calling css_tryget if
+ * the mem_cgroup is used for charging. (dropping refcnt from swap can be
+ * called against removed memcg.)
  */
 static struct mem_cgroup *mem_cgroup_lookup(unsigned short id)
 {
@@ -2676,13 +2675,6 @@ 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:
@@ -2696,10 +2688,27 @@ out:
         return ret;
 }
 
-/*
- * move charges to its parent.
+/**
+ * mem_cgroup_move_parent - moves page to the parent group
+ * @page: the page to move
+ * @pc: page_cgroup of the page
+ * @child: page's cgroup
+ *
+ * move charges to its parent or the root cgroup if the group has no
+ * parent (aka use_hierarchy==0).
+ * Although this might fail (get_page_unless_zero, isolate_lru_page or
+ * mem_cgroup_move_account fails) the failure is always temporary and
+ * it signals a race with a page removal/uncharge or migration. In the
+ * first case the page is on the way out and it will vanish from the LRU
+ * on the next attempt and the call should be retried later.
+ * Isolation from the LRU fails only if page has been isolated from
+ * the LRU since we looked at it and that usually means either global
+ * reclaim or migration going on. The page will either get back to the
+ * LRU or vanish.
+ * Finaly mem_cgroup_move_account fails only if the page got uncharged
+ * (!PageCgroupUsed) or moved to a different group. The page will
+ * disappear in the next attempt.
  */
-
 static int mem_cgroup_move_parent(struct page *page,
                                   struct page_cgroup *pc,
                                   struct mem_cgroup *child)
@@ -2709,9 +2718,7 @@ static int mem_cgroup_move_parent(struct page *page,
         unsigned long uninitialized_var(flags);
         int ret;
 
-        /* Is ROOT ? */
-        if (mem_cgroup_is_root(child))
-                return -EINVAL;
+        VM_BUG_ON(mem_cgroup_is_root(child));
 
         ret = -EBUSY;
         if (!get_page_unless_zero(page))
@@ -2728,8 +2735,10 @@ static int mem_cgroup_move_parent(struct page *page,
         if (!parent)
                 parent = root_mem_cgroup;
 
-        if (nr_pages > 1)
+        if (nr_pages > 1) {
+                VM_BUG_ON(!PageTransHuge(page));
                 flags = compound_lock_irqsave(page);
+        }
 
         ret = mem_cgroup_move_account(page, nr_pages,
                                 pc, child, parent);
@@ -2871,7 +2880,6 @@ __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);
         /*
@@ -2885,12 +2893,6 @@ __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,
@@ -3338,8 +3340,7 @@ 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;
@@ -3373,13 +3374,6 @@ 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);
 }
 
 /*
@@ -3679,17 +3673,22 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
         return nr_reclaimed;
 }
 
-/*
+/**
+ * mem_cgroup_force_empty_list - clears LRU of a group
+ * @memcg: group to clear
+ * @node: NUMA node
+ * @zid: zone id
+ * @lru: lru to to clear
+ *
  * Traverse a specified page_cgroup list and try to drop them all.  This doesn't
- * reclaim the pages page themselves - it just removes the page_cgroups.
- * Returns true if some page_cgroups were not freed, indicating that the caller
- * must retry this operation.
+ * reclaim the pages page themselves - pages are moved to the parent (or root)
+ * group.
  */
-static bool mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
+static void mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
                                 int node, int zid, enum lru_list lru)
 {
         struct mem_cgroup_per_zone *mz;
-        unsigned long flags, loop;
+        unsigned long flags;
         struct list_head *list;
         struct page *busy;
         struct zone *zone;
@@ -3698,11 +3697,8 @@ static bool mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
         mz = mem_cgroup_zoneinfo(memcg, node, zid);
         list = &mz->lruvec.lists[lru];
 
-        loop = mz->lru_size[lru];
-        /* give some margin against EBUSY etc...*/
-        loop += 256;
         busy = NULL;
-        while (loop--) {
+        do {
                 struct page_cgroup *pc;
                 struct page *page;
 
@@ -3728,76 +3724,72 @@ static bool mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
                         cond_resched();
                 } else
                         busy = NULL;
-        }
-        return !list_empty(list);
+        } while (!list_empty(list));
 }
 
 /*
- * make mem_cgroup's charge to be 0 if there is no task.
+ * make mem_cgroup's charge to be 0 if there is no task by moving
+ * all the charges and pages to the parent.
  * This enables deleting this mem_cgroup.
+ *
+ * Caller is responsible for holding css reference on the memcg.
  */
-static int mem_cgroup_force_empty(struct mem_cgroup *memcg, bool free_all)
+static void mem_cgroup_reparent_charges(struct mem_cgroup *memcg)
 {
-        int ret;
-        int node, zid, shrink;
-        int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
-        struct cgroup *cgrp = memcg->css.cgroup;
-
-        css_get(&memcg->css);
+        int node, zid;
 
-        shrink = 0;
-        /* should free all ? */
-        if (free_all)
-                goto try_to_free;
-move_account:
         do {
-                ret = -EBUSY;
-                if (cgroup_task_count(cgrp) || !list_empty(&cgrp->children))
-                        goto out;
                 /* This is for making all *used* pages to be on LRU. */
                 lru_add_drain_all();
                 drain_all_stock_sync(memcg);
-                ret = 0;
                 mem_cgroup_start_move(memcg);
                 for_each_node_state(node, N_HIGH_MEMORY) {
-                        for (zid = 0; !ret && zid < MAX_NR_ZONES; zid++) {
+                        for (zid = 0; zid < MAX_NR_ZONES; zid++) {
                                 enum lru_list lru;
                                 for_each_lru(lru) {
-                                        ret = mem_cgroup_force_empty_list(memcg,
+                                        mem_cgroup_force_empty_list(memcg,
                                                         node, zid, lru);
-                                        if (ret)
-                                                break;
                                 }
                         }
-                        if (ret)
-                                break;
                 }
                 mem_cgroup_end_move(memcg);
                 memcg_oom_recover(memcg);
                 cond_resched();
-        /* "ret" should also be checked to ensure all lists are empty. */
-        } while (res_counter_read_u64(&memcg->res, RES_USAGE) > 0 || ret);
-out:
-        css_put(&memcg->css);
-        return ret;
 
-try_to_free:
+                /*
+                 * This is a safety check because mem_cgroup_force_empty_list
+                 * could have raced with mem_cgroup_replace_page_cache callers
+                 * so the lru seemed empty but the page could have been added
+                 * right after the check. RES_USAGE should be safe as we always
+                 * charge before adding to the LRU.
+                 */
+        } while (res_counter_read_u64(&memcg->res, RES_USAGE) > 0);
+}
+
+/*
+ * Reclaims as many pages from the given memcg as possible and moves
+ * the rest to the parent.
+ *
+ * Caller is responsible for holding css reference for memcg.
+ */
+static int mem_cgroup_force_empty(struct mem_cgroup *memcg)
+{
+        int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
+        struct cgroup *cgrp = memcg->css.cgroup;
+
         /* returns EBUSY if there is a task or if we come here twice. */
-        if (cgroup_task_count(cgrp) || !list_empty(&cgrp->children) || shrink) {
-                ret = -EBUSY;
-                goto out;
-        }
+        if (cgroup_task_count(cgrp) || !list_empty(&cgrp->children))
+                return -EBUSY;
+
         /* we call try-to-free pages for make this cgroup empty */
         lru_add_drain_all();
         /* try to free all pages in this cgroup */
-        shrink = 1;
         while (nr_retries && res_counter_read_u64(&memcg->res, RES_USAGE) > 0) {
                 int progress;
 
-                if (signal_pending(current)) {
-                        ret = -EINTR;
-                        goto out;
-                }
+                if (signal_pending(current))
+                        return -EINTR;
+
                 progress = try_to_free_mem_cgroup_pages(memcg, GFP_KERNEL,
                                                 false);
                 if (!progress) {
@@ -3808,13 +3800,23 @@ try_to_free:
 
         }
         lru_add_drain();
-        /* try move_account...there may be some *locked* pages. */
-        goto move_account;
+        mem_cgroup_reparent_charges(memcg);
+
+        return 0;
 }
 
 static int mem_cgroup_force_empty_write(struct cgroup *cont, unsigned int event)
 {
-        return mem_cgroup_force_empty(mem_cgroup_from_cont(cont), true);
+        struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
+        int ret;
+
+        if (mem_cgroup_is_root(memcg))
+                return -EINVAL;
+        css_get(&memcg->css);
+        ret = mem_cgroup_force_empty(memcg);
+        css_put(&memcg->css);
+
+        return ret;
 }
 
 
@@ -5001,11 +5003,11 @@ free_out:
         return ERR_PTR(error);
 }
 
-static int mem_cgroup_pre_destroy(struct cgroup *cont)
+static void mem_cgroup_pre_destroy(struct cgroup *cont)
 {
         struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
 
-        return mem_cgroup_force_empty(memcg, false);
+        mem_cgroup_reparent_charges(memcg);
 }
 
 static void mem_cgroup_destroy(struct cgroup *cont)
@@ -5607,7 +5609,6 @@ struct cgroup_subsys mem_cgroup_subsys = {
         .base_cftypes = mem_cgroup_files,
         .early_init = 0,
         .use_id = 1,
-        .__DEPRECATED_clear_css_refs = true,
 };
 
 #ifdef CONFIG_MEMCG_SWAP