Merge branch 'for-3.11' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Pull cgroup changes from Tejun Heo:
 "This pull request contains the following changes.

   - cgroup_subsys_state (css) reference counting has been converted to
     percpu-ref.  css is what each resource controller embeds into its
     own control structure and perform reference count against.  It may
     be used in hot paths of various subsystems and is similar to module
     refcnt in that aspect.  For example, block-cgroup's css refcnting
     was showing up a lot in Mikulaus's device-mapper scalability work
     and this should alleviate it.

   - cgroup subtree iterator has been updated so that RCU read lock can
     be released after grabbing reference.  This allows simplifying its
     users which requires blocking which used to build iteration list
     under RCU read lock and then traverse it outside.  This pull
     request contains simplification of cgroup core and device-cgroup.
     A separate pull request will update cpuset.

   - Fixes for various bugs including corner race conditions and RCU
     usage bugs.

   - A lot of cleanups and some prepartory work for the planned unified
     hierarchy support."

* 'for-3.11' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup: (48 commits)
  cgroup: CGRP_ROOT_SUBSYS_BOUND should also be ignored when mounting an existing hierarchy
  cgroup: CGRP_ROOT_SUBSYS_BOUND should be ignored when comparing mount options
  cgroup: fix deadlock on cgroup_mutex via drop_parsed_module_refcounts()
  cgroup: always use RCU accessors for protected accesses
  cgroup: fix RCU accesses around task->cgroups
  cgroup: fix RCU accesses to task->cgroups
  cgroup: grab cgroup_mutex in drop_parsed_module_refcounts()
  cgroup: fix cgroupfs_root early destruction path
  cgroup: reserve ID 0 for dummy_root and 1 for unified hierarchy
  cgroup: implement for_each_[builtin_]subsys()
  cgroup: move init_css_set initialization inside cgroup_mutex
  cgroup: s/for_each_subsys()/for_each_root_subsys()/
  cgroup: clean up find_css_set() and friends
  cgroup: remove cgroup->actual_subsys_mask
  cgroup: prefix global variables with "cgroup_"
  cgroup: convert CFTYPE_* flags to enums
  cgroup: rename cont to cgrp
  cgroup: clean up cgroup_serial_nr_cursor
  cgroup: convert cgroup_cft_commit() to use cgroup_for_each_descendant_pre()
  cgroup: make serial_nr_cursor available throughout cgroup.c
  ...

include/linux/cgroup.h

@@ -20,6 +20,7 @@
 #include <linux/workqueue.h>
 #include <linux/xattr.h>
 #include <linux/fs.h>
+#include <linux/percpu-refcount.h>
 
 #ifdef CONFIG_CGROUPS
 
@@ -72,13 +73,8 @@ struct cgroup_subsys_state {
 	 */
 	struct cgroup *cgroup;
 
-	/*
-	 * State maintained by the cgroup system to allow subsystems
-	 * to be "busy". Should be accessed via css_get(),
-	 * css_tryget() and css_put().
-	 */
-
-	atomic_t refcnt;
+	/* reference count - access via css_[try]get() and css_put() */
+	struct percpu_ref refcnt;
 
 	unsigned long flags;
 	/* ID for this css, if possible */
@@ -94,56 +90,52 @@ enum {
 	CSS_ONLINE	= (1 << 1), /* between ->css_online() and ->css_offline() */
 };
 
-/* Caller must verify that the css is not for root cgroup */
-static inline void __css_get(struct cgroup_subsys_state *css, int count)
-{
-	atomic_add(count, &css->refcnt);
-}
-
-/*
- * Call css_get() to hold a reference on the css; it can be used
- * for a reference obtained via:
- * - an existing ref-counted reference to the css
- * - task->cgroups for a locked task
+/**
+ * css_get - obtain a reference on the specified css
+ * @css: target css
+ *
+ * The caller must already have a reference.
  */
-
 static inline void css_get(struct cgroup_subsys_state *css)
 {
 	/* We don't need to reference count the root state */
 	if (!(css->flags & CSS_ROOT))
-		__css_get(css, 1);
+		percpu_ref_get(&css->refcnt);
 }
 
-/*
- * Call css_tryget() to take a reference on a css if your existing
- * (known-valid) reference isn't already ref-counted. Returns false if
- * the css has been destroyed.
+/**
+ * css_tryget - try to obtain a reference on the specified css
+ * @css: target css
+ *
+ * Obtain a reference on @css if it's alive.  The caller naturally needs to
+ * ensure that @css is accessible but doesn't have to be holding a
+ * reference on it - IOW, RCU protected access is good enough for this
+ * function.  Returns %true if a reference count was successfully obtained;
+ * %false otherwise.
  */
-
-extern bool __css_tryget(struct cgroup_subsys_state *css);
 static inline bool css_tryget(struct cgroup_subsys_state *css)
 {
 	if (css->flags & CSS_ROOT)
 		return true;
-	return __css_tryget(css);
+	return percpu_ref_tryget(&css->refcnt);
 }
 
-/*
- * css_put() should be called to release a reference taken by
- * css_get() or css_tryget()
+/**
+ * css_put - put a css reference
+ * @css: target css
+ *
+ * Put a reference obtained via css_get() and css_tryget().
  */
-
-extern void __css_put(struct cgroup_subsys_state *css);
 static inline void css_put(struct cgroup_subsys_state *css)
 {
 	if (!(css->flags & CSS_ROOT))
-		__css_put(css);
+		percpu_ref_put(&css->refcnt);
 }
 
 /* bits in struct cgroup flags field */
 enum {
 	/* Control Group is dead */
-	CGRP_REMOVED,
+	CGRP_DEAD,
 	/*
 	 * Control Group has previously had a child cgroup or a task,
 	 * but no longer (only if CGRP_NOTIFY_ON_RELEASE is set)
@@ -169,12 +161,6 @@ struct cgroup_name {
 struct cgroup {
 	unsigned long flags;		/* "unsigned long" so bitops work */
 
-	/*
-	 * count users of this cgroup. >0 means busy, but doesn't
-	 * necessarily indicate the number of tasks in the cgroup
-	 */
-	atomic_t count;
-
 	int id;				/* ida allocated in-hierarchy ID */
 
 	/*
@@ -188,6 +174,14 @@ struct cgroup {
 	struct cgroup *parent;		/* my parent */
 	struct dentry *dentry;		/* cgroup fs entry, RCU protected */
 
+	/*
+	 * Monotonically increasing unique serial number which defines a
+	 * uniform order among all cgroups.  It's guaranteed that all
+	 * ->children lists are in the ascending order of ->serial_nr.
+	 * It's used to allow interrupting and resuming iterations.
+	 */
+	u64 serial_nr;
+
 	/*
 	 * This is a copy of dentry->d_name, and it's needed because
 	 * we can't use dentry->d_name in cgroup_path().
@@ -207,13 +201,10 @@ struct cgroup {
 	struct cgroupfs_root *root;
 
 	/*
-	 * List of cg_cgroup_links pointing at css_sets with
-	 * tasks in this cgroup. Protected by css_set_lock
+	 * List of cgrp_cset_links pointing at css_sets with tasks in this
+	 * cgroup.  Protected by css_set_lock.
 	 */
-	struct list_head css_sets;
-
-	struct list_head allcg_node;	/* cgroupfs_root->allcg_list */
-	struct list_head cft_q_node;	/* used during cftype add/rm */
+	struct list_head cset_links;
 
 	/*
 	 * Linked list running through all cgroups that can
@@ -229,9 +220,10 @@ struct cgroup {
 	struct list_head pidlists;
 	struct mutex pidlist_mutex;
 
-	/* For RCU-protected deletion */
+	/* For css percpu_ref killing and RCU-protected deletion */
 	struct rcu_head rcu_head;
-	struct work_struct free_work;
+	struct work_struct destroy_work;
+	atomic_t css_kill_cnt;
 
 	/* List of events which userspace want to receive */
 	struct list_head event_list;
@@ -269,18 +261,26 @@ enum {
 	 *
 	 * - Remount is disallowed.
 	 *
+	 * - "tasks" is removed.  Everything should be at process
+	 *   granularity.  Use "cgroup.procs" instead.
+	 *
+	 * - "release_agent" and "notify_on_release" are removed.
+	 *   Replacement notification mechanism will be implemented.
+	 *
+	 * - rename(2) is disallowed.
+	 *
 	 * - memcg: use_hierarchy is on by default and the cgroup file for
 	 *   the flag is not created.
-	 *
-	 * The followings are planned changes.
-	 *
-	 * - release_agent will be disallowed once replacement notification
-	 *   mechanism is implemented.
 	 */
 	CGRP_ROOT_SANE_BEHAVIOR	= (1 << 0),
 
 	CGRP_ROOT_NOPREFIX	= (1 << 1), /* mounted subsystems have no named prefix */
 	CGRP_ROOT_XATTR		= (1 << 2), /* supports extended attributes */
+
+	/* mount options live below bit 16 */
+	CGRP_ROOT_OPTION_MASK	= (1 << 16) - 1,
+
+	CGRP_ROOT_SUBSYS_BOUND	= (1 << 16), /* subsystems finished binding */
 };
 
 /*
@@ -291,18 +291,12 @@ enum {
 struct cgroupfs_root {
 	struct super_block *sb;
 
-	/*
-	 * The bitmask of subsystems intended to be attached to this
-	 * hierarchy
-	 */
+	/* The bitmask of subsystems attached to this hierarchy */
 	unsigned long subsys_mask;
 
 	/* Unique id for this hierarchy. */
 	int hierarchy_id;
 
-	/* The bitmask of subsystems currently attached to this hierarchy */
-	unsigned long actual_subsys_mask;
-
 	/* A list running through the attached subsystems */
 	struct list_head subsys_list;
 
@@ -315,9 +309,6 @@ struct cgroupfs_root {
 	/* A list running through the active hierarchies */
 	struct list_head root_list;
 
-	/* All cgroups on this root, cgroup_mutex protected */
-	struct list_head allcg_list;
-
 	/* Hierarchy-specific flags */
 	unsigned long flags;
 
@@ -357,11 +348,10 @@ struct css_set {
 	struct list_head tasks;
 
 	/*
-	 * List of cg_cgroup_link objects on link chains from
-	 * cgroups referenced from this css_set. Protected by
-	 * css_set_lock
+	 * List of cgrp_cset_links pointing at cgroups referenced from this
+	 * css_set.  Protected by css_set_lock.
 	 */
-	struct list_head cg_links;
+	struct list_head cgrp_links;
 
 	/*
 	 * Set of subsystem states, one for each subsystem. This array
@@ -394,9 +384,11 @@ struct cgroup_map_cb {
  */
 
 /* cftype->flags */
-#define CFTYPE_ONLY_ON_ROOT	(1U << 0)	/* only create on root cg */
-#define CFTYPE_NOT_ON_ROOT	(1U << 1)	/* don't create on root cg */
-#define CFTYPE_INSANE		(1U << 2)	/* don't create if sane_behavior */
+enum {
+	CFTYPE_ONLY_ON_ROOT	= (1 << 0),	/* only create on root cg */
+	CFTYPE_NOT_ON_ROOT	= (1 << 1),	/* don't create on root cg */
+	CFTYPE_INSANE		= (1 << 2),	/* don't create if sane_behavior */
+};
 
 #define MAX_CFTYPE_NAME		64
 
@@ -442,13 +434,13 @@ struct cftype {
 	 * entry. The key/value pairs (and their ordering) should not
 	 * change between reboots.
 	 */
-	int (*read_map)(struct cgroup *cont, struct cftype *cft,
+	int (*read_map)(struct cgroup *cgrp, struct cftype *cft,
 			struct cgroup_map_cb *cb);
 	/*
 	 * read_seq_string() is used for outputting a simple sequence
 	 * using seqfile.
 	 */
-	int (*read_seq_string)(struct cgroup *cont, struct cftype *cft,
+	int (*read_seq_string)(struct cgroup *cgrp, struct cftype *cft,
 			       struct seq_file *m);
 
 	ssize_t (*write)(struct cgroup *cgrp, struct cftype *cft,
@@ -538,10 +530,11 @@ static inline const char *cgroup_name(const struct cgroup *cgrp)
 int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
 int cgroup_rm_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
 
-int cgroup_is_removed(const struct cgroup *cgrp);
 bool cgroup_is_descendant(struct cgroup *cgrp, struct cgroup *ancestor);
 
 int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen);
+int task_cgroup_path_from_hierarchy(struct task_struct *task, int hierarchy_id,
+				    char *buf, size_t buflen);
 
 int cgroup_task_count(const struct cgroup *cgrp);
 
@@ -646,22 +639,60 @@ static inline struct cgroup_subsys_state *cgroup_subsys_state(
 	return cgrp->subsys[subsys_id];
 }
 
-/*
- * function to get the cgroup_subsys_state which allows for extra
- * rcu_dereference_check() conditions, such as locks used during the
- * cgroup_subsys::attach() methods.
+/**
+ * task_css_set_check - obtain a task's css_set with extra access conditions
+ * @task: the task to obtain css_set for
+ * @__c: extra condition expression to be passed to rcu_dereference_check()
+ *
+ * A task's css_set is RCU protected, initialized and exited while holding
+ * task_lock(), and can only be modified while holding both cgroup_mutex
+ * and task_lock() while the task is alive.  This macro verifies that the
+ * caller is inside proper critical section and returns @task's css_set.
+ *
+ * The caller can also specify additional allowed conditions via @__c, such
+ * as locks used during the cgroup_subsys::attach() methods.
  */
 #ifdef CONFIG_PROVE_RCU
 extern struct mutex cgroup_mutex;
-#define task_subsys_state_check(task, subsys_id, __c)			\
-	rcu_dereference_check((task)->cgroups->subsys[(subsys_id)],	\
-			      lockdep_is_held(&(task)->alloc_lock) ||	\
-			      lockdep_is_held(&cgroup_mutex) || (__c))
+#define task_css_set_check(task, __c)					\
+	rcu_dereference_check((task)->cgroups,				\
+		lockdep_is_held(&(task)->alloc_lock) ||			\
+		lockdep_is_held(&cgroup_mutex) || (__c))
 #else
-#define task_subsys_state_check(task, subsys_id, __c)			\
-	rcu_dereference((task)->cgroups->subsys[(subsys_id)])
+#define task_css_set_check(task, __c)					\
+	rcu_dereference((task)->cgroups)
 #endif
 
+/**
+ * task_subsys_state_check - obtain css for (task, subsys) w/ extra access conds
+ * @task: the target task
+ * @subsys_id: the target subsystem ID
+ * @__c: extra condition expression to be passed to rcu_dereference_check()
+ *
+ * Return the cgroup_subsys_state for the (@task, @subsys_id) pair.  The
+ * synchronization rules are the same as task_css_set_check().
+ */
+#define task_subsys_state_check(task, subsys_id, __c)			\
+	task_css_set_check((task), (__c))->subsys[(subsys_id)]
+
+/**
+ * task_css_set - obtain a task's css_set
+ * @task: the task to obtain css_set for
+ *
+ * See task_css_set_check().
+ */
+static inline struct css_set *task_css_set(struct task_struct *task)
+{
+	return task_css_set_check(task, false);
+}
+
+/**
+ * task_subsys_state - obtain css for (task, subsys)
+ * @task: the target task
+ * @subsys_id: the target subsystem ID
+ *
+ * See task_subsys_state_check().
+ */
 static inline struct cgroup_subsys_state *
 task_subsys_state(struct task_struct *task, int subsys_id)
 {
@@ -674,12 +705,14 @@ static inline struct cgroup* task_cgroup(struct task_struct *task,
 	return task_subsys_state(task, subsys_id)->cgroup;
 }
 
+struct cgroup *cgroup_next_sibling(struct cgroup *pos);
+
 /**
  * cgroup_for_each_child - iterate through children of a cgroup
  * @pos: the cgroup * to use as the loop cursor
- * @cgroup: cgroup whose children to walk
+ * @cgrp: cgroup whose children to walk
  *
- * Walk @cgroup's children.  Must be called under rcu_read_lock().  A child
+ * Walk @cgrp's children.  Must be called under rcu_read_lock().  A child
  * cgroup which hasn't finished ->css_online() or already has finished
  * ->css_offline() may show up during traversal and it's each subsystem's
  * responsibility to verify that each @pos is alive.
@@ -687,9 +720,15 @@ static inline struct cgroup* task_cgroup(struct task_struct *task,
  * If a subsystem synchronizes against the parent in its ->css_online() and
  * before starting iterating, a cgroup which finished ->css_online() is
  * guaranteed to be visible in the future iterations.
+ *
+ * It is allowed to temporarily drop RCU read lock during iteration.  The
+ * caller is responsible for ensuring that @pos remains accessible until
+ * the start of the next iteration by, for example, bumping the css refcnt.
  */
-#define cgroup_for_each_child(pos, cgroup)				\
-	list_for_each_entry_rcu(pos, &(cgroup)->children, sibling)
+#define cgroup_for_each_child(pos, cgrp)				\
+	for ((pos) = list_first_or_null_rcu(&(cgrp)->children,		\
+					    struct cgroup, sibling);	\
+	     (pos); (pos) = cgroup_next_sibling((pos)))
 
 struct cgroup *cgroup_next_descendant_pre(struct cgroup *pos,
 					  struct cgroup *cgroup);
@@ -748,6 +787,10 @@ struct cgroup *cgroup_rightmost_descendant(struct cgroup *pos);
  * Alternatively, a subsystem may choose to use a single global lock to
  * synchronize ->css_online() and ->css_offline() against tree-walking
  * operations.
+ *
+ * It is allowed to temporarily drop RCU read lock during iteration.  The
+ * caller is responsible for ensuring that @pos remains accessible until
+ * the start of the next iteration by, for example, bumping the css refcnt.
  */
 #define cgroup_for_each_descendant_pre(pos, cgroup)			\
 	for (pos = cgroup_next_descendant_pre(NULL, (cgroup)); (pos);	\
@@ -771,7 +814,7 @@ struct cgroup *cgroup_next_descendant_post(struct cgroup *pos,
 
 /* A cgroup_iter should be treated as an opaque object */
 struct cgroup_iter {
-	struct list_head *cg_link;
+	struct list_head *cset_link;
 	struct list_head *task;
 };
 
@@ -827,7 +870,6 @@ bool css_is_ancestor(struct cgroup_subsys_state *cg,
 
 /* Get id and depth of css */
 unsigned short css_id(struct cgroup_subsys_state *css);
-unsigned short css_depth(struct cgroup_subsys_state *css);
 struct cgroup_subsys_state *cgroup_css_from_dir(struct file *f, int id);
 
 #else /* !CONFIG_CGROUPS */
@@ -838,8 +880,6 @@ static inline void cgroup_fork(struct task_struct *p) {}
 static inline void cgroup_post_fork(struct task_struct *p) {}
 static inline void cgroup_exit(struct task_struct *p, int callbacks) {}
 
-static inline void cgroup_lock(void) {}
-static inline void cgroup_unlock(void) {}
 static inline int cgroupstats_build(struct cgroupstats *stats,
 					struct dentry *dentry)
 {

security/device_cgroup.c

@@ -49,8 +49,6 @@ struct dev_cgroup {
 	struct cgroup_subsys_state css;
 	struct list_head exceptions;
 	enum devcg_behavior behavior;
-	/* temporary list for pending propagation operations */
-	struct list_head propagate_pending;
 };
 
 static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
@@ -241,7 +239,6 @@ static struct cgroup_subsys_state *devcgroup_css_alloc(struct cgroup *cgroup)
 	if (!dev_cgroup)
 		return ERR_PTR(-ENOMEM);
 	INIT_LIST_HEAD(&dev_cgroup->exceptions);
-	INIT_LIST_HEAD(&dev_cgroup->propagate_pending);
 	dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
 
 	return &dev_cgroup->css;
@@ -444,34 +441,6 @@ static void revalidate_active_exceptions(struct dev_cgroup *devcg)
 	}
 }
 
-/**
- * get_online_devcg - walks the cgroup tree and fills a list with the online
- * 		      groups
- * @root: cgroup used as starting point
- * @online: list that will be filled with online groups
- *
- * Must be called with devcgroup_mutex held. Grabs RCU lock.
- * Because devcgroup_mutex is held, no devcg will become online or offline
- * during the tree walk (see devcgroup_online, devcgroup_offline)
- * A separated list is needed because propagate_behavior() and
- * propagate_exception() need to allocate memory and can block.
- */
-static void get_online_devcg(struct cgroup *root, struct list_head *online)
-{
-	struct cgroup *pos;
-	struct dev_cgroup *devcg;
-
-	lockdep_assert_held(&devcgroup_mutex);
-
-	rcu_read_lock();
-	cgroup_for_each_descendant_pre(pos, root) {
-		devcg = cgroup_to_devcgroup(pos);
-		if (is_devcg_online(devcg))
-			list_add_tail(&devcg->propagate_pending, online);
-	}
-	rcu_read_unlock();
-}
-
 /**
  * propagate_exception - propagates a new exception to the children
  * @devcg_root: device cgroup that added a new exception
@@ -482,15 +451,24 @@ static void get_online_devcg(struct cgroup *root, struct list_head *online)
 static int propagate_exception(struct dev_cgroup *devcg_root,
 			       struct dev_exception_item *ex)
 {
-	struct cgroup *root = devcg_root->css.cgroup;
-	struct dev_cgroup *devcg, *parent, *tmp;
+	struct cgroup *root = devcg_root->css.cgroup, *pos;
 	int rc = 0;
-	LIST_HEAD(pending);
 
-	get_online_devcg(root, &pending);
+	rcu_read_lock();
 
-	list_for_each_entry_safe(devcg, tmp, &pending, propagate_pending) {
-		parent = cgroup_to_devcgroup(devcg->css.cgroup->parent);
+	cgroup_for_each_descendant_pre(pos, root) {
+		struct dev_cgroup *devcg = cgroup_to_devcgroup(pos);
+
+		/*
+		 * Because devcgroup_mutex is held, no devcg will become
+		 * online or offline during the tree walk (see on/offline
+		 * methods), and online ones are safe to access outside RCU
+		 * read lock without bumping refcnt.
+		 */
+		if (!is_devcg_online(devcg))
+			continue;
+
+		rcu_read_unlock();
 
 		/*
 		 * in case both root's behavior and devcg is allow, a new
@@ -512,8 +490,10 @@ static int propagate_exception(struct dev_cgroup *devcg_root,
 		}
 		revalidate_active_exceptions(devcg);
 
-		list_del_init(&devcg->propagate_pending);
+		rcu_read_lock();
 	}
+
+	rcu_read_unlock();
 	return rc;
 }