Merge branch 'for-3.6' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Pull cgroup changes from Tejun Heo:
 "Nothing too interesting.  A minor bug fix and some cleanups."

* 'for-3.6' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroup: Update remount documentation
  cgroup: cgroup_rm_files() was calling simple_unlink() with the wrong inode
  cgroup: Remove populate() documentation
  cgroup: remove hierarchy_mutex

Documentation/cgroups/cgroups.txt

@@ -370,15 +370,12 @@ To mount a cgroup hierarchy with just the cpuset and memory
 subsystems, type:
 # mount -t cgroup -o cpuset,memory hier1 /sys/fs/cgroup/rg1
 
-To change the set of subsystems bound to a mounted hierarchy, just
-remount with different options:
-# mount -o remount,cpuset,blkio hier1 /sys/fs/cgroup/rg1
-
-Now memory is removed from the hierarchy and blkio is added.
-
-Note this will add blkio to the hierarchy but won't remove memory or
-cpuset, because the new options are appended to the old ones:
-# mount -o remount,blkio /sys/fs/cgroup/rg1
+While remounting cgroups is currently supported, it is not recommend
+to use it. Remounting allows changing bound subsystems and
+release_agent. Rebinding is hardly useful as it only works when the
+hierarchy is empty and release_agent itself should be replaced with
+conventional fsnotify. The support for remounting will be removed in
+the future.
 
 To Specify a hierarchy's release_agent:
 # mount -t cgroup -o cpuset,release_agent="/sbin/cpuset_release_agent" \
@@ -637,16 +634,6 @@ void exit(struct task_struct *task)
 
 Called during task exit.
 
-int populate(struct cgroup *cgrp)
-(cgroup_mutex held by caller)
-
-Called after creation of a cgroup to allow a subsystem to populate
-the cgroup directory with file entries.  The subsystem should make
-calls to cgroup_add_file() with objects of type cftype (see
-include/linux/cgroup.h for details).  Note that although this
-method can return an error code, the error code is currently not
-always handled well.
-
 void post_clone(struct cgroup *cgrp)
 (cgroup_mutex held by caller)
 
@@ -656,7 +643,7 @@ example in cpusets, no task may attach before 'cpus' and 'mems' are set
 up.
 
 void bind(struct cgroup *root)
-(cgroup_mutex and ss->hierarchy_mutex held by caller)
+(cgroup_mutex held by caller)
 
 Called when a cgroup subsystem is rebound to a different hierarchy
 and root cgroup. Currently this will only involve movement between

include/linux/cgroup.h

@@ -499,22 +499,9 @@ struct cgroup_subsys {
 #define MAX_CGROUP_TYPE_NAMELEN 32
 	const char *name;
 
-	/*
-	 * Protects sibling/children links of cgroups in this
-	 * hierarchy, plus protects which hierarchy (or none) the
-	 * subsystem is a part of (i.e. root/sibling).  To avoid
-	 * potential deadlocks, the following operations should not be
-	 * undertaken while holding any hierarchy_mutex:
-	 *
-	 * - allocating memory
-	 * - initiating hotplug events
-	 */
-	struct mutex hierarchy_mutex;
-	struct lock_class_key subsys_key;
-
 	/*
 	 * Link to parent, and list entry in parent's children.
-	 * Protected by this->hierarchy_mutex and cgroup_lock()
+	 * Protected by cgroup_lock()
 	 */
 	struct cgroupfs_root *root;
 	struct list_head sibling;
@@ -602,7 +589,7 @@ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *);
  * the lifetime of cgroup_subsys_state is subsys's matter.
  *
  * Looking up and scanning function should be called under rcu_read_lock().
- * Taking cgroup_mutex()/hierarchy_mutex() is not necessary for following calls.
+ * Taking cgroup_mutex is not necessary for following calls.
  * But the css returned by this routine can be "not populated yet" or "being
  * destroyed". The caller should check css and cgroup's status.
  */

kernel/cgroup.c

@@ -954,7 +954,7 @@ static int cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
 
 		dget(d);
 		d_delete(d);
-		simple_unlink(d->d_inode, d);
+		simple_unlink(cgrp->dentry->d_inode, d);
 		list_del_init(&cfe->node);
 		dput(d);
 
@@ -1068,28 +1068,24 @@ static int rebind_subsystems(struct cgroupfs_root *root,
 			BUG_ON(cgrp->subsys[i]);
 			BUG_ON(!dummytop->subsys[i]);
 			BUG_ON(dummytop->subsys[i]->cgroup != dummytop);
-			mutex_lock(&ss->hierarchy_mutex);
 			cgrp->subsys[i] = dummytop->subsys[i];
 			cgrp->subsys[i]->cgroup = cgrp;
 			list_move(&ss->sibling, &root->subsys_list);
 			ss->root = root;
 			if (ss->bind)
 				ss->bind(cgrp);
-			mutex_unlock(&ss->hierarchy_mutex);
 			/* refcount was already taken, and we're keeping it */
 		} else if (bit & removed_bits) {
 			/* We're removing this subsystem */
 			BUG_ON(ss == NULL);
 			BUG_ON(cgrp->subsys[i] != dummytop->subsys[i]);
 			BUG_ON(cgrp->subsys[i]->cgroup != cgrp);
-			mutex_lock(&ss->hierarchy_mutex);
 			if (ss->bind)
 				ss->bind(dummytop);
 			dummytop->subsys[i]->cgroup = dummytop;
 			cgrp->subsys[i] = NULL;
 			subsys[i]->root = &rootnode;
 			list_move(&ss->sibling, &rootnode.subsys_list);
-			mutex_unlock(&ss->hierarchy_mutex);
 			/* subsystem is now free - drop reference on module */
 			module_put(ss->module);
 		} else if (bit & final_bits) {
@@ -3915,37 +3911,6 @@ static void init_cgroup_css(struct cgroup_subsys_state *css,
 		set_bit(CSS_CLEAR_CSS_REFS, &css->flags);
 }
 
-static void cgroup_lock_hierarchy(struct cgroupfs_root *root)
-{
-	/* We need to take each hierarchy_mutex in a consistent order */
-	int i;
-
-	/*
-	 * No worry about a race with rebind_subsystems that might mess up the
-	 * locking order, since both parties are under cgroup_mutex.
-	 */
-	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
-		struct cgroup_subsys *ss = subsys[i];
-		if (ss == NULL)
-			continue;
-		if (ss->root == root)
-			mutex_lock(&ss->hierarchy_mutex);
-	}
-}
-
-static void cgroup_unlock_hierarchy(struct cgroupfs_root *root)
-{
-	int i;
-
-	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
-		struct cgroup_subsys *ss = subsys[i];
-		if (ss == NULL)
-			continue;
-		if (ss->root == root)
-			mutex_unlock(&ss->hierarchy_mutex);
-	}
-}
-
 /*
  * cgroup_create - create a cgroup
  * @parent: cgroup that will be parent of the new cgroup
@@ -4006,9 +3971,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
 			ss->post_clone(cgrp);
 	}
 
-	cgroup_lock_hierarchy(root);
 	list_add(&cgrp->sibling, &cgrp->parent->children);
-	cgroup_unlock_hierarchy(root);
 	root->number_of_cgroups++;
 
 	err = cgroup_create_dir(cgrp, dentry, mode);
@@ -4035,9 +3998,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
 
  err_remove:
 
-	cgroup_lock_hierarchy(root);
 	list_del(&cgrp->sibling);
-	cgroup_unlock_hierarchy(root);
 	root->number_of_cgroups--;
 
  err_destroy:
@@ -4245,10 +4206,8 @@ again:
 		list_del_init(&cgrp->release_list);
 	raw_spin_unlock(&release_list_lock);
 
-	cgroup_lock_hierarchy(cgrp->root);
 	/* delete this cgroup from parent->children */
 	list_del_init(&cgrp->sibling);
-	cgroup_unlock_hierarchy(cgrp->root);
 
 	list_del_init(&cgrp->allcg_node);
 
@@ -4322,8 +4281,6 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
 	 * need to invoke fork callbacks here. */
 	BUG_ON(!list_empty(&init_task.tasks));
 
-	mutex_init(&ss->hierarchy_mutex);
-	lockdep_set_class(&ss->hierarchy_mutex, &ss->subsys_key);
 	ss->active = 1;
 
 	/* this function shouldn't be used with modular subsystems, since they
@@ -4450,8 +4407,6 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
 	}
 	write_unlock(&css_set_lock);
 
-	mutex_init(&ss->hierarchy_mutex);
-	lockdep_set_class(&ss->hierarchy_mutex, &ss->subsys_key);
 	ss->active = 1;
 
 	/* success! */