Merge branch 'perf/core' into perf/uprobes

Merge in latest upstream (and the latest perf development tree),
to prepare for tooling changes, and also to pick up v3.4 MM
changes that the uprobes code needs to take care of.

Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 148 insertions, 208 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index a5d3b5325f7..ed64ccac67c 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -818,7 +818,7 @@ static int cgroup_call_pre_destroy(struct cgroup *cgrp)
 
 	for_each_subsys(cgrp->root, ss)
 		if (ss->pre_destroy) {
-			ret = ss->pre_destroy(ss, cgrp);
+			ret = ss->pre_destroy(cgrp);
 			if (ret)
 				break;
 		}
@@ -846,7 +846,7 @@ static void cgroup_diput(struct dentry *dentry, struct inode *inode)
 		 * Release the subsystem state objects.
 		 */
 		for_each_subsys(cgrp->root, ss)
-			ss->destroy(ss, cgrp);
+			ss->destroy(cgrp);
 
 		cgrp->root->number_of_cgroups--;
 		mutex_unlock(&cgroup_mutex);
@@ -1015,7 +1015,7 @@ static int rebind_subsystems(struct cgroupfs_root *root,
 			list_move(&ss->sibling, &root->subsys_list);
 			ss->root = root;
 			if (ss->bind)
-				ss->bind(ss, cgrp);
+				ss->bind(cgrp);
 			mutex_unlock(&ss->hierarchy_mutex);
 			/* refcount was already taken, and we're keeping it */
 		} else if (bit & removed_bits) {
@@ -1025,7 +1025,7 @@ static int rebind_subsystems(struct cgroupfs_root *root,
 			BUG_ON(cgrp->subsys[i]->cgroup != cgrp);
 			mutex_lock(&ss->hierarchy_mutex);
 			if (ss->bind)
-				ss->bind(ss, dummytop);
+				ss->bind(dummytop);
 			dummytop->subsys[i]->cgroup = dummytop;
 			cgrp->subsys[i] = NULL;
 			subsys[i]->root = &rootnode;
@@ -1472,7 +1472,6 @@ static int cgroup_get_rootdir(struct super_block *sb)
 
 	struct inode *inode =
 		cgroup_new_inode(S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR, sb);
-	struct dentry *dentry;
 
 	if (!inode)
 		return -ENOMEM;
@@ -1481,12 +1480,9 @@ static int cgroup_get_rootdir(struct super_block *sb)
 	inode->i_op = &cgroup_dir_inode_operations;
 	/* directories start off with i_nlink == 2 (for "." entry) */
 	inc_nlink(inode);
-	dentry = d_alloc_root(inode);
-	if (!dentry) {
-		iput(inode);
+	sb->s_root = d_make_root(inode);
+	if (!sb->s_root)
 		return -ENOMEM;
-	}
-	sb->s_root = dentry;
 	/* for everything else we want ->d_op set */
 	sb->s_d_op = &cgroup_dops;
 	return 0;
@@ -1763,6 +1759,7 @@ EXPORT_SYMBOL_GPL(cgroup_path);
 struct task_and_cgroup {
 	struct task_struct	*task;
 	struct cgroup		*cgrp;
+	struct css_set		*cg;
 };
 
 struct cgroup_taskset {
@@ -1843,11 +1840,10 @@ EXPORT_SYMBOL_GPL(cgroup_taskset_size);
  * will already exist. If not set, this function might sleep, and can fail with
  * -ENOMEM. Must be called with cgroup_mutex and threadgroup locked.
  */
-static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp,
-			       struct task_struct *tsk, bool guarantee)
+static void cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp,
+				struct task_struct *tsk, struct css_set *newcg)
 {
 	struct css_set *oldcg;
-	struct css_set *newcg;
 
 	/*
 	 * We are synchronized through threadgroup_lock() against PF_EXITING
@@ -1857,23 +1853,6 @@ static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp,
 	WARN_ON_ONCE(tsk->flags & PF_EXITING);
 	oldcg = tsk->cgroups;
 
-	/* locate or allocate a new css_set for this task. */
-	if (guarantee) {
-		/* we know the css_set we want already exists. */
-		struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT];
-		read_lock(&css_set_lock);
-		newcg = find_existing_css_set(oldcg, cgrp, template);
-		BUG_ON(!newcg);
-		get_css_set(newcg);
-		read_unlock(&css_set_lock);
-	} else {
-		might_sleep();
-		/* find_css_set will give us newcg already referenced. */
-		newcg = find_css_set(oldcg, cgrp);
-		if (!newcg)
-			return -ENOMEM;
-	}
-
 	task_lock(tsk);
 	rcu_assign_pointer(tsk->cgroups, newcg);
 	task_unlock(tsk);
@@ -1892,7 +1871,6 @@ static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp,
 	put_css_set(oldcg);
 
 	set_bit(CGRP_RELEASABLE, &oldcgrp->flags);
-	return 0;
 }
 
 /**
@@ -1905,11 +1883,12 @@ static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp,
  */
 int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
 {
-	int retval;
+	int retval = 0;
 	struct cgroup_subsys *ss, *failed_ss = NULL;
 	struct cgroup *oldcgrp;
 	struct cgroupfs_root *root = cgrp->root;
 	struct cgroup_taskset tset = { };
+	struct css_set *newcg;
 
 	/* @tsk either already exited or can't exit until the end */
 	if (tsk->flags & PF_EXITING)
@@ -1925,7 +1904,7 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
 
 	for_each_subsys(root, ss) {
 		if (ss->can_attach) {
-			retval = ss->can_attach(ss, cgrp, &tset);
+			retval = ss->can_attach(cgrp, &tset);
 			if (retval) {
 				/*
 				 * Remember on which subsystem the can_attach()
@@ -1939,13 +1918,17 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
 		}
 	}
 
-	retval = cgroup_task_migrate(cgrp, oldcgrp, tsk, false);
-	if (retval)
+	newcg = find_css_set(tsk->cgroups, cgrp);
+	if (!newcg) {
+		retval = -ENOMEM;
 		goto out;
+	}
+
+	cgroup_task_migrate(cgrp, oldcgrp, tsk, newcg);
 
 	for_each_subsys(root, ss) {
 		if (ss->attach)
-			ss->attach(ss, cgrp, &tset);
+			ss->attach(cgrp, &tset);
 	}
 
 	synchronize_rcu();
@@ -1967,7 +1950,7 @@ out:
 				 */
 				break;
 			if (ss->cancel_attach)
-				ss->cancel_attach(ss, cgrp, &tset);
+				ss->cancel_attach(cgrp, &tset);
 		}
 	}
 	return retval;
@@ -1997,66 +1980,6 @@ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
 }
 EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
 
-/*
- * cgroup_attach_proc works in two stages, the first of which prefetches all
- * new css_sets needed (to make sure we have enough memory before committing
- * to the move) and stores them in a list of entries of the following type.
- * TODO: possible optimization: use css_set->rcu_head for chaining instead
- */
-struct cg_list_entry {
-	struct css_set *cg;
-	struct list_head links;
-};
-
-static bool css_set_check_fetched(struct cgroup *cgrp,
-				  struct task_struct *tsk, struct css_set *cg,
-				  struct list_head *newcg_list)
-{
-	struct css_set *newcg;
-	struct cg_list_entry *cg_entry;
-	struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT];
-
-	read_lock(&css_set_lock);
-	newcg = find_existing_css_set(cg, cgrp, template);
-	read_unlock(&css_set_lock);
-
-	/* doesn't exist at all? */
-	if (!newcg)
-		return false;
-	/* see if it's already in the list */
-	list_for_each_entry(cg_entry, newcg_list, links)
-		if (cg_entry->cg == newcg)
-			return true;
-
-	/* not found */
-	return false;
-}
-
-/*
- * Find the new css_set and store it in the list in preparation for moving the
- * given task to the given cgroup. Returns 0 or -ENOMEM.
- */
-static int css_set_prefetch(struct cgroup *cgrp, struct css_set *cg,
-			    struct list_head *newcg_list)
-{
-	struct css_set *newcg;
-	struct cg_list_entry *cg_entry;
-
-	/* ensure a new css_set will exist for this thread */
-	newcg = find_css_set(cg, cgrp);
-	if (!newcg)
-		return -ENOMEM;
-	/* add it to the list */
-	cg_entry = kmalloc(sizeof(struct cg_list_entry), GFP_KERNEL);
-	if (!cg_entry) {
-		put_css_set(newcg);
-		return -ENOMEM;
-	}
-	cg_entry->cg = newcg;
-	list_add(&cg_entry->links, newcg_list);
-	return 0;
-}
-
 /**
  * cgroup_attach_proc - attach all threads in a threadgroup to a cgroup
  * @cgrp: the cgroup to attach to
@@ -2070,20 +1993,12 @@ static int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
 	int retval, i, group_size;
 	struct cgroup_subsys *ss, *failed_ss = NULL;
 	/* guaranteed to be initialized later, but the compiler needs this */
-	struct css_set *oldcg;
 	struct cgroupfs_root *root = cgrp->root;
 	/* threadgroup list cursor and array */
 	struct task_struct *tsk;
 	struct task_and_cgroup *tc;
 	struct flex_array *group;
 	struct cgroup_taskset tset = { };
-	/*
-	 * we need to make sure we have css_sets for all the tasks we're
-	 * going to move -before- we actually start moving them, so that in
-	 * case we get an ENOMEM we can bail out before making any changes.
-	 */
-	struct list_head newcg_list;
-	struct cg_list_entry *cg_entry, *temp_nobe;
 
 	/*
 	 * step 0: in order to do expensive, possibly blocking operations for
@@ -2102,23 +2017,14 @@ static int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
 	if (retval)
 		goto out_free_group_list;
 
-	/* prevent changes to the threadgroup list while we take a snapshot. */
-	read_lock(&tasklist_lock);
-	if (!thread_group_leader(leader)) {
-		/*
-		 * a race with de_thread from another thread's exec() may strip
-		 * us of our leadership, making while_each_thread unsafe to use
-		 * on this task. if this happens, there is no choice but to
-		 * throw this task away and try again (from cgroup_procs_write);
-		 * this is "double-double-toil-and-trouble-check locking".
-		 */
-		read_unlock(&tasklist_lock);
-		retval = -EAGAIN;
-		goto out_free_group_list;
-	}
-
 	tsk = leader;
 	i = 0;
+	/*
+	 * Prevent freeing of tasks while we take a snapshot. Tasks that are
+	 * already PF_EXITING could be freed from underneath us unless we
+	 * take an rcu_read_lock.
+	 */
+	rcu_read_lock();
 	do {
 		struct task_and_cgroup ent;
 
@@ -2128,24 +2034,24 @@ static int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
 
 		/* as per above, nr_threads may decrease, but not increase. */
 		BUG_ON(i >= group_size);
-		/*
-		 * saying GFP_ATOMIC has no effect here because we did prealloc
-		 * earlier, but it's good form to communicate our expectations.
-		 */
 		ent.task = tsk;
 		ent.cgrp = task_cgroup_from_root(tsk, root);
 		/* nothing to do if this task is already in the cgroup */
 		if (ent.cgrp == cgrp)
 			continue;
+		/*
+		 * saying GFP_ATOMIC has no effect here because we did prealloc
+		 * earlier, but it's good form to communicate our expectations.
+		 */
 		retval = flex_array_put(group, i, &ent, GFP_ATOMIC);
 		BUG_ON(retval != 0);
 		i++;
 	} while_each_thread(leader, tsk);
+	rcu_read_unlock();
 	/* remember the number of threads in the array for later. */
 	group_size = i;
 	tset.tc_array = group;
 	tset.tc_array_len = group_size;
-	read_unlock(&tasklist_lock);
 
 	/* methods shouldn't be called if no task is actually migrating */
 	retval = 0;
@@ -2157,7 +2063,7 @@ static int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
 	 */
 	for_each_subsys(root, ss) {
 		if (ss->can_attach) {
-			retval = ss->can_attach(ss, cgrp, &tset);
+			retval = ss->can_attach(cgrp, &tset);
 			if (retval) {
 				failed_ss = ss;
 				goto out_cancel_attach;
@@ -2169,17 +2075,12 @@ static int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
 	 * step 2: make sure css_sets exist for all threads to be migrated.
 	 * we use find_css_set, which allocates a new one if necessary.
 	 */
-	INIT_LIST_HEAD(&newcg_list);
 	for (i = 0; i < group_size; i++) {
 		tc = flex_array_get(group, i);
-		oldcg = tc->task->cgroups;
-
-		/* if we don't already have it in the list get a new one */
-		if (!css_set_check_fetched(cgrp, tc->task, oldcg,
-					   &newcg_list)) {
-			retval = css_set_prefetch(cgrp, oldcg, &newcg_list);
-			if (retval)
-				goto out_list_teardown;
+		tc->cg = find_css_set(tc->task->cgroups, cgrp);
+		if (!tc->cg) {
+			retval = -ENOMEM;
+			goto out_put_css_set_refs;
 		}
 	}
 
@@ -2190,8 +2091,7 @@ static int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
 	 */
 	for (i = 0; i < group_size; i++) {
 		tc = flex_array_get(group, i);
-		retval = cgroup_task_migrate(cgrp, tc->cgrp, tc->task, true);
-		BUG_ON(retval);
+		cgroup_task_migrate(cgrp, tc->cgrp, tc->task, tc->cg);
 	}
 	/* nothing is sensitive to fork() after this point. */
 
@@ -2200,7 +2100,7 @@ static int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
 	 */
 	for_each_subsys(root, ss) {
 		if (ss->attach)
-			ss->attach(ss, cgrp, &tset);
+			ss->attach(cgrp, &tset);
 	}
 
 	/*
@@ -2209,21 +2109,22 @@ static int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
 	synchronize_rcu();
 	cgroup_wakeup_rmdir_waiter(cgrp);
 	retval = 0;
-out_list_teardown:
-	/* clean up the list of prefetched css_sets. */
-	list_for_each_entry_safe(cg_entry, temp_nobe, &newcg_list, links) {
-		list_del(&cg_entry->links);
-		put_css_set(cg_entry->cg);
-		kfree(cg_entry);
+out_put_css_set_refs:
+	if (retval) {
+		for (i = 0; i < group_size; i++) {
+			tc = flex_array_get(group, i);
+			if (!tc->cg)
+				break;
+			put_css_set(tc->cg);
+		}
 	}
 out_cancel_attach:
-	/* same deal as in cgroup_attach_task */
 	if (retval) {
 		for_each_subsys(root, ss) {
 			if (ss == failed_ss)
 				break;
 			if (ss->cancel_attach)
-				ss->cancel_attach(ss, cgrp, &tset);
+				ss->cancel_attach(cgrp, &tset);
 		}
 	}
 out_free_group_list:
@@ -2245,22 +2146,14 @@ static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
 	if (!cgroup_lock_live_group(cgrp))
 		return -ENODEV;
 
+retry_find_task:
+	rcu_read_lock();
 	if (pid) {
-		rcu_read_lock();
 		tsk = find_task_by_vpid(pid);
 		if (!tsk) {
 			rcu_read_unlock();
-			cgroup_unlock();
-			return -ESRCH;
-		}
-		if (threadgroup) {
-			/*
-			 * RCU protects this access, since tsk was found in the
-			 * tid map. a race with de_thread may cause group_leader
-			 * to stop being the leader, but cgroup_attach_proc will
-			 * detect it later.
-			 */
-			tsk = tsk->group_leader;
+			ret= -ESRCH;
+			goto out_unlock_cgroup;
 		}
 		/*
 		 * even if we're attaching all tasks in the thread group, we
@@ -2271,29 +2164,38 @@ static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
 		    cred->euid != tcred->uid &&
 		    cred->euid != tcred->suid) {
 			rcu_read_unlock();
-			cgroup_unlock();
-			return -EACCES;
+			ret = -EACCES;
+			goto out_unlock_cgroup;
 		}
-		get_task_struct(tsk);
-		rcu_read_unlock();
-	} else {
-		if (threadgroup)
-			tsk = current->group_leader;
-		else
-			tsk = current;
-		get_task_struct(tsk);
-	}
-
-	threadgroup_lock(tsk);
+	} else
+		tsk = current;
 
 	if (threadgroup)
+		tsk = tsk->group_leader;
+	get_task_struct(tsk);
+	rcu_read_unlock();
+
+	threadgroup_lock(tsk);
+	if (threadgroup) {
+		if (!thread_group_leader(tsk)) {
+			/*
+			 * a race with de_thread from another thread's exec()
+			 * may strip us of our leadership, if this happens,
+			 * there is no choice but to throw this task away and
+			 * try again; this is
+			 * "double-double-toil-and-trouble-check locking".
+			 */
+			threadgroup_unlock(tsk);
+			put_task_struct(tsk);
+			goto retry_find_task;
+		}
 		ret = cgroup_attach_proc(cgrp, tsk);
-	else
+	} else
 		ret = cgroup_attach_task(cgrp, tsk);
-
 	threadgroup_unlock(tsk);
 
 	put_task_struct(tsk);
+out_unlock_cgroup:
 	cgroup_unlock();
 	return ret;
 }
@@ -2305,16 +2207,7 @@ static int cgroup_tasks_write(struct cgroup *cgrp, struct cftype *cft, u64 pid)
 
 static int cgroup_procs_write(struct cgroup *cgrp, struct cftype *cft, u64 tgid)
 {
-	int ret;
-	do {
-		/*
-		 * attach_proc fails with -EAGAIN if threadgroup leadership
-		 * changes in the middle of the operation, in which case we need
-		 * to find the task_struct for the new leader and start over.
-		 */
-		ret = attach_task_by_pid(cgrp, tgid, true);
-	} while (ret == -EAGAIN);
-	return ret;
+	return attach_task_by_pid(cgrp, tgid, true);
 }
 
 /**
@@ -2804,15 +2697,20 @@ static void cgroup_advance_iter(struct cgroup *cgrp,
  * using their cgroups capability, we don't maintain the lists running
  * through each css_set to its tasks until we see the list actually
  * used - in other words after the first call to cgroup_iter_start().
- *
- * The tasklist_lock is not held here, as do_each_thread() and
- * while_each_thread() are protected by RCU.
  */
 static void cgroup_enable_task_cg_lists(void)
 {
 	struct task_struct *p, *g;
 	write_lock(&css_set_lock);
 	use_task_css_set_links = 1;
+	/*
+	 * We need tasklist_lock because RCU is not safe against
+	 * while_each_thread(). Besides, a forking task that has passed
+	 * cgroup_post_fork() without seeing use_task_css_set_links = 1
+	 * is not guaranteed to have its child immediately visible in the
+	 * tasklist if we walk through it with RCU.
+	 */
+	read_lock(&tasklist_lock);
 	do_each_thread(g, p) {
 		task_lock(p);
 		/*
@@ -2824,6 +2722,7 @@ static void cgroup_enable_task_cg_lists(void)
 			list_add(&p->cg_list, &p->cgroups->tasks);
 		task_unlock(p);
 	} while_each_thread(g, p);
+	read_unlock(&tasklist_lock);
 	write_unlock(&css_set_lock);
 }
 
@@ -3043,6 +2942,38 @@ int cgroup_scan_tasks(struct cgroup_scanner *scan)
  *
  */
 
+/* which pidlist file are we talking about? */
+enum cgroup_filetype {
+	CGROUP_FILE_PROCS,
+	CGROUP_FILE_TASKS,
+};
+
+/*
+ * A pidlist is a list of pids that virtually represents the contents of one
+ * of the cgroup files ("procs" or "tasks"). We keep a list of such pidlists,
+ * a pair (one each for procs, tasks) for each pid namespace that's relevant
+ * to the cgroup.
+ */
+struct cgroup_pidlist {
+	/*
+	 * used to find which pidlist is wanted. doesn't change as long as
+	 * this particular list stays in the list.
+	*/
+	struct { enum cgroup_filetype type; struct pid_namespace *ns; } key;
+	/* array of xids */
+	pid_t *list;
+	/* how many elements the above list has */
+	int length;
+	/* how many files are using the current array */
+	int use_count;
+	/* each of these stored in a list by its cgroup */
+	struct list_head links;
+	/* pointer to the cgroup we belong to, for list removal purposes */
+	struct cgroup *owner;
+	/* protects the other fields */
+	struct rw_semaphore mutex;
+};
+
 /*
  * The following two functions "fix" the issue where there are more pids
  * than kmalloc will give memory for; in such cases, we use vmalloc/vfree.
@@ -3827,7 +3758,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
 		set_bit(CGRP_CLONE_CHILDREN, &cgrp->flags);
 
 	for_each_subsys(root, ss) {
-		struct cgroup_subsys_state *css = ss->create(ss, cgrp);
+		struct cgroup_subsys_state *css = ss->create(cgrp);
 
 		if (IS_ERR(css)) {
 			err = PTR_ERR(css);
@@ -3841,7 +3772,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
 		}
 		/* At error, ->destroy() callback has to free assigned ID. */
 		if (clone_children(parent) && ss->post_clone)
-			ss->post_clone(ss, cgrp);
+			ss->post_clone(cgrp);
 	}
 
 	cgroup_lock_hierarchy(root);
@@ -3875,7 +3806,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
 
 	for_each_subsys(root, ss) {
 		if (cgrp->subsys[ss->subsys_id])
-			ss->destroy(ss, cgrp);
+			ss->destroy(cgrp);
 	}
 
 	mutex_unlock(&cgroup_mutex);
@@ -4099,7 +4030,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
 	/* Create the top cgroup state for this subsystem */
 	list_add(&ss->sibling, &rootnode.subsys_list);
 	ss->root = &rootnode;
-	css = ss->create(ss, dummytop);
+	css = ss->create(dummytop);
 	/* We don't handle early failures gracefully */
 	BUG_ON(IS_ERR(css));
 	init_cgroup_css(css, ss, dummytop);
@@ -4188,7 +4119,7 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
 	 * no ss->create seems to need anything important in the ss struct, so
 	 * this can happen first (i.e. before the rootnode attachment).
 	 */
-	css = ss->create(ss, dummytop);
+	css = ss->create(dummytop);
 	if (IS_ERR(css)) {
 		/* failure case - need to deassign the subsys[] slot. */
 		subsys[i] = NULL;
@@ -4206,7 +4137,7 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
 		int ret = cgroup_init_idr(ss, css);
 		if (ret) {
 			dummytop->subsys[ss->subsys_id] = NULL;
-			ss->destroy(ss, dummytop);
+			ss->destroy(dummytop);
 			subsys[i] = NULL;
 			mutex_unlock(&cgroup_mutex);
 			return ret;
@@ -4304,7 +4235,7 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss)
 	 * pointer to find their state. note that this also takes care of
 	 * freeing the css_id.
 	 */
-	ss->destroy(ss, dummytop);
+	ss->destroy(dummytop);
 	dummytop->subsys[ss->subsys_id] = NULL;
 
 	mutex_unlock(&cgroup_mutex);
@@ -4580,7 +4511,7 @@ void cgroup_fork_callbacks(struct task_struct *child)
 		for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
 			struct cgroup_subsys *ss = subsys[i];
 			if (ss->fork)
-				ss->fork(ss, child);
+				ss->fork(child);
 		}
 	}
 }
@@ -4596,6 +4527,17 @@ void cgroup_fork_callbacks(struct task_struct *child)
  */
 void cgroup_post_fork(struct task_struct *child)
 {
+	/*
+	 * use_task_css_set_links is set to 1 before we walk the tasklist
+	 * under the tasklist_lock and we read it here after we added the child
+	 * to the tasklist under the tasklist_lock as well. If the child wasn't
+	 * yet in the tasklist when we walked through it from
+	 * cgroup_enable_task_cg_lists(), then use_task_css_set_links value
+	 * should be visible now due to the paired locking and barriers implied
+	 * by LOCK/UNLOCK: it is written before the tasklist_lock unlock
+	 * in cgroup_enable_task_cg_lists() and read here after the tasklist_lock
+	 * lock on fork.
+	 */
 	if (use_task_css_set_links) {
 		write_lock(&css_set_lock);
 		if (list_empty(&child->cg_list)) {
@@ -4682,7 +4624,7 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks)
 				struct cgroup *old_cgrp =
 					rcu_dereference_raw(cg->subsys[i])->cgroup;
 				struct cgroup *cgrp = task_cgroup(tsk, i);
-				ss->exit(ss, cgrp, old_cgrp, tsk);
+				ss->exit(cgrp, old_cgrp, tsk);
 			}
 		}
 	}
@@ -4939,9 +4881,9 @@ void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css)
 
 	rcu_assign_pointer(id->css, NULL);
 	rcu_assign_pointer(css->id, NULL);
-	write_lock(&ss->id_lock);
+	spin_lock(&ss->id_lock);
 	idr_remove(&ss->idr, id->id);
-	write_unlock(&ss->id_lock);
+	spin_unlock(&ss->id_lock);
 	kfree_rcu(id, rcu_head);
 }
 EXPORT_SYMBOL_GPL(free_css_id);
@@ -4967,10 +4909,10 @@ static struct css_id *get_new_cssid(struct cgroup_subsys *ss, int depth)
 		error = -ENOMEM;
 		goto err_out;
 	}
-	write_lock(&ss->id_lock);
+	spin_lock(&ss->id_lock);
 	/* Don't use 0. allocates an ID of 1-65535 */
 	error = idr_get_new_above(&ss->idr, newid, 1, &myid);
-	write_unlock(&ss->id_lock);
+	spin_unlock(&ss->id_lock);
 
 	/* Returns error when there are no free spaces for new ID.*/
 	if (error) {
@@ -4985,9 +4927,9 @@ static struct css_id *get_new_cssid(struct cgroup_subsys *ss, int depth)
 	return newid;
 remove_idr:
 	error = -ENOSPC;
-	write_lock(&ss->id_lock);
+	spin_lock(&ss->id_lock);
 	idr_remove(&ss->idr, myid);
-	write_unlock(&ss->id_lock);
+	spin_unlock(&ss->id_lock);
 err_out:
 	kfree(newid);
 	return ERR_PTR(error);
@@ -4999,7 +4941,7 @@ static int __init_or_module cgroup_init_idr(struct cgroup_subsys *ss,
 {
 	struct css_id *newid;
 
-	rwlock_init(&ss->id_lock);
+	spin_lock_init(&ss->id_lock);
 	idr_init(&ss->idr);
 
 	newid = get_new_cssid(ss, 0);
@@ -5087,6 +5029,8 @@ css_get_next(struct cgroup_subsys *ss, int id,
 		return NULL;
 
 	BUG_ON(!ss->use_id);
+	WARN_ON_ONCE(!rcu_read_lock_held());
+
 	/* fill start point for scan */
 	tmpid = id;
 	while (1) {
@@ -5094,10 +5038,7 @@ css_get_next(struct cgroup_subsys *ss, int id,
 		 * scan next entry from bitmap(tree), tmpid is updated after
 		 * idr_get_next().
 		 */
-		read_lock(&ss->id_lock);
 		tmp = idr_get_next(&ss->idr, &tmpid);
-		read_unlock(&ss->id_lock);
-
 		if (!tmp)
 			break;
 		if (tmp->depth >= depth && tmp->stack[depth] == rootid) {
@@ -5137,8 +5078,7 @@ struct cgroup_subsys_state *cgroup_css_from_dir(struct file *f, int id)
 }
 
 #ifdef CONFIG_CGROUP_DEBUG
-static struct cgroup_subsys_state *debug_create(struct cgroup_subsys *ss,
-						   struct cgroup *cont)
+static struct cgroup_subsys_state *debug_create(struct cgroup *cont)
 {
 	struct cgroup_subsys_state *css = kzalloc(sizeof(*css), GFP_KERNEL);
 
@@ -5148,7 +5088,7 @@ static struct cgroup_subsys_state *debug_create(struct cgroup_subsys *ss,
 	return css;
 }
 
-static void debug_destroy(struct cgroup_subsys *ss, struct cgroup *cont)
+static void debug_destroy(struct cgroup *cont)
 {
 	kfree(cont->subsys[debug_subsys_id]);
 }