Merge branch 'cgroup-rmdir-updates' into cgroup/for-3.8

Pull rmdir updates into for-3.8 so that further callback updates can
be put on top.  This pull created a trivial conflict between the
following two commits.

  8c7f6edbda ("cgroup: mark subsystems with broken hierarchy support and whine if cgroups are nested for them")
  ed95779340 ("cgroup: kill cgroup_subsys->__DEPRECATED_clear_css_refs")

The former added a field to cgroup_subsys and the latter removed one
from it.  They happen to be colocated causing the conflict.  Keeping
what's added and removing what's removed resolves the conflict.

Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 61 insertions, 195 deletions

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();