Merge tag 'cgroup-for-6.1' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Pull cgroup updates from Tejun Heo:

 - cpuset now support isolated cpus.partition type, which will enable
   dynamic CPU isolation

 - pids.peak added to remember the max number of pids used

 - holes in cgroup namespace plugged

 - internal cleanups

* tag 'cgroup-for-6.1' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup: (25 commits)
  cgroup: use strscpy() is more robust and safer
  iocost_monitor: reorder BlkgIterator
  cgroup: simplify code in cgroup_apply_control
  cgroup: Make cgroup_get_from_id() prettier
  cgroup/cpuset: remove unreachable code
  cgroup: Remove CFTYPE_PRESSURE
  cgroup: Improve cftype add/rm error handling
  kselftest/cgroup: Add cpuset v2 partition root state test
  cgroup/cpuset: Update description of cpuset.cpus.partition in cgroup-v2.rst
  cgroup/cpuset: Make partition invalid if cpumask change violates exclusivity rule
  cgroup/cpuset: Relocate a code block in validate_change()
  cgroup/cpuset: Show invalid partition reason string
  cgroup/cpuset: Add a new isolated cpus.partition type
  cgroup/cpuset: Relax constraints to partition & cpus changes
  cgroup/cpuset: Allow no-task partition to have empty cpuset.cpus.effective
  cgroup/cpuset: Miscellaneous cleanups & add helper functions
  cgroup/cpuset: Enable update_tasks_cpumask() on top_cpuset
  cgroup: add pids.peak interface for pids controller
  cgroup: Remove data-race around cgrp_dfl_visible
  cgroup: Fix build failure when CONFIG_SHRINKER_DEBUG
  ...

5 files changed, 663 insertions, 342 deletions

diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
index 36b740cb3d59..2c7ecca226be 100644
--- a/kernel/cgroup/cgroup-internal.h
+++ b/kernel/cgroup/cgroup-internal.h
@@ -250,6 +250,8 @@ int cgroup_migrate(struct task_struct *leader, bool threadgroup,
 
 int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
 		       bool threadgroup);
+void cgroup_attach_lock(bool lock_threadgroup);
+void cgroup_attach_unlock(bool lock_threadgroup);
 struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup,
 					     bool *locked)
 	__acquires(&cgroup_threadgroup_rwsem);
diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index ff6a8099eb2a..52bb5a74a23b 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -59,8 +59,7 @@ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
 	int retval = 0;
 
 	mutex_lock(&cgroup_mutex);
-	cpus_read_lock();
-	percpu_down_write(&cgroup_threadgroup_rwsem);
+	cgroup_attach_lock(true);
 	for_each_root(root) {
 		struct cgroup *from_cgrp;
 
@@ -72,8 +71,7 @@ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
 		if (retval)
 			break;
 	}
-	percpu_up_write(&cgroup_threadgroup_rwsem);
-	cpus_read_unlock();
+	cgroup_attach_unlock(true);
 	mutex_unlock(&cgroup_mutex);
 
 	return retval;
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index b6e3110b3ea7..764bdd5fd8d1 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -217,6 +217,7 @@ struct cgroup_namespace init_cgroup_ns = {
 
 static struct file_system_type cgroup2_fs_type;
 static struct cftype cgroup_base_files[];
+static struct cftype cgroup_psi_files[];
 
 /* cgroup optional features */
 enum cgroup_opt_features {
@@ -1689,12 +1690,16 @@ static void css_clear_dir(struct cgroup_subsys_state *css)
 	css->flags &= ~CSS_VISIBLE;
 
 	if (!css->ss) {
-		if (cgroup_on_dfl(cgrp))
-			cfts = cgroup_base_files;
-		else
-			cfts = cgroup1_base_files;
-
-		cgroup_addrm_files(css, cgrp, cfts, false);
+		if (cgroup_on_dfl(cgrp)) {
+			cgroup_addrm_files(css, cgrp,
+					   cgroup_base_files, false);
+			if (cgroup_psi_enabled())
+				cgroup_addrm_files(css, cgrp,
+						   cgroup_psi_files, false);
+		} else {
+			cgroup_addrm_files(css, cgrp,
+					   cgroup1_base_files, false);
+		}
 	} else {
 		list_for_each_entry(cfts, &css->ss->cfts, node)
 			cgroup_addrm_files(css, cgrp, cfts, false);
@@ -1717,14 +1722,22 @@ static int css_populate_dir(struct cgroup_subsys_state *css)
 		return 0;
 
 	if (!css->ss) {
-		if (cgroup_on_dfl(cgrp))
-			cfts = cgroup_base_files;
-		else
-			cfts = cgroup1_base_files;
-
-		ret = cgroup_addrm_files(&cgrp->self, cgrp, cfts, true);
-		if (ret < 0)
-			return ret;
+		if (cgroup_on_dfl(cgrp)) {
+			ret = cgroup_addrm_files(&cgrp->self, cgrp,
+						 cgroup_base_files, true);
+			if (ret < 0)
+				return ret;
+
+			if (cgroup_psi_enabled()) {
+				ret = cgroup_addrm_files(&cgrp->self, cgrp,
+							 cgroup_psi_files, true);
+				if (ret < 0)
+					return ret;
+			}
+		} else {
+			cgroup_addrm_files(css, cgrp,
+					   cgroup1_base_files, true);
+		}
 	} else {
 		list_for_each_entry(cfts, &css->ss->cfts, node) {
 			ret = cgroup_addrm_files(css, cgrp, cfts, true);
@@ -2050,7 +2063,7 @@ int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
 	}
 	root_cgrp->kn = kernfs_root_to_node(root->kf_root);
 	WARN_ON_ONCE(cgroup_ino(root_cgrp) != 1);
-	root_cgrp->ancestor_ids[0] = cgroup_id(root_cgrp);
+	root_cgrp->ancestors[0] = root_cgrp;
 
 	ret = css_populate_dir(&root_cgrp->self);
 	if (ret)
@@ -2173,7 +2186,7 @@ static int cgroup_get_tree(struct fs_context *fc)
 	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
 	int ret;
 
-	cgrp_dfl_visible = true;
+	WRITE_ONCE(cgrp_dfl_visible, true);
 	cgroup_get_live(&cgrp_dfl_root.cgrp);
 	ctx->root = &cgrp_dfl_root;
 
@@ -2361,7 +2374,7 @@ int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
 		ret = cgroup_path_ns_locked(cgrp, buf, buflen, &init_cgroup_ns);
 	} else {
 		/* if no hierarchy exists, everyone is in "/" */
-		ret = strlcpy(buf, "/", buflen);
+		ret = strscpy(buf, "/", buflen);
 	}
 
 	spin_unlock_irq(&css_set_lock);
@@ -2393,7 +2406,7 @@ EXPORT_SYMBOL_GPL(task_cgroup_path);
  * write-locking cgroup_threadgroup_rwsem. This allows ->attach() to assume that
  * CPU hotplug is disabled on entry.
  */
-static void cgroup_attach_lock(bool lock_threadgroup)
+void cgroup_attach_lock(bool lock_threadgroup)
 {
 	cpus_read_lock();
 	if (lock_threadgroup)
@@ -2404,7 +2417,7 @@ static void cgroup_attach_lock(bool lock_threadgroup)
  * cgroup_attach_unlock - Undo cgroup_attach_lock()
  * @lock_threadgroup: whether to up_write cgroup_threadgroup_rwsem
  */
-static void cgroup_attach_unlock(bool lock_threadgroup)
+void cgroup_attach_unlock(bool lock_threadgroup)
 {
 	if (lock_threadgroup)
 		percpu_up_write(&cgroup_threadgroup_rwsem);
@@ -3292,11 +3305,7 @@ static int cgroup_apply_control(struct cgroup *cgrp)
 	 * making the following cgroup_update_dfl_csses() properly update
 	 * css associations of all tasks in the subtree.
 	 */
-	ret = cgroup_update_dfl_csses(cgrp);
-	if (ret)
-		return ret;
-
-	return 0;
+	return cgroup_update_dfl_csses(cgrp);
 }
 
 /**
@@ -4132,8 +4141,6 @@ static int cgroup_addrm_files(struct cgroup_subsys_state *css,
 restart:
 	for (cft = cfts; cft != cft_end && cft->name[0] != '\0'; cft++) {
 		/* does cft->flags tell us to skip this file on @cgrp? */
-		if ((cft->flags & CFTYPE_PRESSURE) && !cgroup_psi_enabled())
-			continue;
 		if ((cft->flags & __CFTYPE_ONLY_ON_DFL) && !cgroup_on_dfl(cgrp))
 			continue;
 		if ((cft->flags & __CFTYPE_NOT_ON_DFL) && cgroup_on_dfl(cgrp))
@@ -4198,21 +4205,25 @@ static void cgroup_exit_cftypes(struct cftype *cfts)
 		cft->ss = NULL;
 
 		/* revert flags set by cgroup core while adding @cfts */
-		cft->flags &= ~(__CFTYPE_ONLY_ON_DFL | __CFTYPE_NOT_ON_DFL);
+		cft->flags &= ~(__CFTYPE_ONLY_ON_DFL | __CFTYPE_NOT_ON_DFL |
+				__CFTYPE_ADDED);
 	}
 }
 
 static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
 {
 	struct cftype *cft;
+	int ret = 0;
 
 	for (cft = cfts; cft->name[0] != '\0'; cft++) {
 		struct kernfs_ops *kf_ops;
 
 		WARN_ON(cft->ss || cft->kf_ops);
 
-		if ((cft->flags & CFTYPE_PRESSURE) && !cgroup_psi_enabled())
-			continue;
+		if (cft->flags & __CFTYPE_ADDED) {
+			ret = -EBUSY;
+			break;
+		}
 
 		if (cft->seq_start)
 			kf_ops = &cgroup_kf_ops;
@@ -4226,26 +4237,26 @@ static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
 		if (cft->max_write_len && cft->max_write_len != PAGE_SIZE) {
 			kf_ops = kmemdup(kf_ops, sizeof(*kf_ops), GFP_KERNEL);
 			if (!kf_ops) {
-				cgroup_exit_cftypes(cfts);
-				return -ENOMEM;
+				ret = -ENOMEM;
+				break;
 			}
 			kf_ops->atomic_write_len = cft->max_write_len;
 		}
 
 		cft->kf_ops = kf_ops;
 		cft->ss = ss;
+		cft->flags |= __CFTYPE_ADDED;
 	}
 
-	return 0;
+	if (ret)
+		cgroup_exit_cftypes(cfts);
+	return ret;
 }
 
 static int cgroup_rm_cftypes_locked(struct cftype *cfts)
 {
 	lockdep_assert_held(&cgroup_mutex);
 
-	if (!cfts || !cfts[0].ss)
-		return -ENOENT;
-
 	list_del(&cfts->node);
 	cgroup_apply_cftypes(cfts, false);
 	cgroup_exit_cftypes(cfts);
@@ -4267,6 +4278,12 @@ int cgroup_rm_cftypes(struct cftype *cfts)
 {
 	int ret;
 
+	if (!cfts || cfts[0].name[0] == '\0')
+		return 0;
+
+	if (!(cfts[0].flags & __CFTYPE_ADDED))
+		return -ENOENT;
+
 	mutex_lock(&cgroup_mutex);
 	ret = cgroup_rm_cftypes_locked(cfts);
 	mutex_unlock(&cgroup_mutex);
@@ -5151,10 +5168,13 @@ static struct cftype cgroup_base_files[] = {
 		.name = "cpu.stat",
 		.seq_show = cpu_stat_show,
 	},
+	{ }	/* terminate */
+};
+
+static struct cftype cgroup_psi_files[] = {
 #ifdef CONFIG_PSI
 	{
 		.name = "io.pressure",
-		.flags = CFTYPE_PRESSURE,
 		.seq_show = cgroup_io_pressure_show,
 		.write = cgroup_io_pressure_write,
 		.poll = cgroup_pressure_poll,
@@ -5162,7 +5182,6 @@ static struct cftype cgroup_base_files[] = {
 	},
 	{
 		.name = "memory.pressure",
-		.flags = CFTYPE_PRESSURE,
 		.seq_show = cgroup_memory_pressure_show,
 		.write = cgroup_memory_pressure_write,
 		.poll = cgroup_pressure_poll,
@@ -5170,7 +5189,6 @@ static struct cftype cgroup_base_files[] = {
 	},
 	{
 		.name = "cpu.pressure",
-		.flags = CFTYPE_PRESSURE,
 		.seq_show = cgroup_cpu_pressure_show,
 		.write = cgroup_cpu_pressure_write,
 		.poll = cgroup_pressure_poll,
@@ -5452,8 +5470,7 @@ static struct cgroup *cgroup_create(struct cgroup *parent, const char *name,
 	int ret;
 
 	/* allocate the cgroup and its ID, 0 is reserved for the root */
-	cgrp = kzalloc(struct_size(cgrp, ancestor_ids, (level + 1)),
-		       GFP_KERNEL);
+	cgrp = kzalloc(struct_size(cgrp, ancestors, (level + 1)), GFP_KERNEL);
 	if (!cgrp)
 		return ERR_PTR(-ENOMEM);
 
@@ -5505,7 +5522,7 @@ static struct cgroup *cgroup_create(struct cgroup *parent, const char *name,
 
 	spin_lock_irq(&css_set_lock);
 	for (tcgrp = cgrp; tcgrp; tcgrp = cgroup_parent(tcgrp)) {
-		cgrp->ancestor_ids[tcgrp->level] = cgroup_id(tcgrp);
+		cgrp->ancestors[tcgrp->level] = tcgrp;
 
 		if (tcgrp != cgrp) {
 			tcgrp->nr_descendants++;
@@ -5938,6 +5955,7 @@ int __init cgroup_init(void)
 
 	BUILD_BUG_ON(CGROUP_SUBSYS_COUNT > 16);
 	BUG_ON(cgroup_init_cftypes(NULL, cgroup_base_files));
+	BUG_ON(cgroup_init_cftypes(NULL, cgroup_psi_files));
 	BUG_ON(cgroup_init_cftypes(NULL, cgroup1_base_files));
 
 	cgroup_rstat_boot();
@@ -6058,19 +6076,22 @@ void cgroup_path_from_kernfs_id(u64 id, char *buf, size_t buflen)
 /*
  * cgroup_get_from_id : get the cgroup associated with cgroup id
  * @id: cgroup id
- * On success return the cgrp, on failure return NULL
+ * On success return the cgrp or ERR_PTR on failure
+ * Only cgroups within current task's cgroup NS are valid.
  */
 struct cgroup *cgroup_get_from_id(u64 id)
 {
 	struct kernfs_node *kn;
-	struct cgroup *cgrp = NULL;
+	struct cgroup *cgrp, *root_cgrp;
 
 	kn = kernfs_find_and_get_node_by_id(cgrp_dfl_root.kf_root, id);
 	if (!kn)
-		goto out;
+		return ERR_PTR(-ENOENT);
 
-	if (kernfs_type(kn) != KERNFS_DIR)
-		goto put;
+	if (kernfs_type(kn) != KERNFS_DIR) {
+		kernfs_put(kn);
+		return ERR_PTR(-ENOENT);
+	}
 
 	rcu_read_lock();
 
@@ -6079,9 +6100,19 @@ struct cgroup *cgroup_get_from_id(u64 id)
 		cgrp = NULL;
 
 	rcu_read_unlock();
-put:
 	kernfs_put(kn);
-out:
+
+	if (!cgrp)
+		return ERR_PTR(-ENOENT);
+
+	spin_lock_irq(&css_set_lock);
+	root_cgrp = current_cgns_cgroup_from_root(&cgrp_dfl_root);
+	spin_unlock_irq(&css_set_lock);
+	if (!cgroup_is_descendant(cgrp, root_cgrp)) {
+		cgroup_put(cgrp);
+		return ERR_PTR(-ENOENT);
+	}
+
 	return cgrp;
 }
 EXPORT_SYMBOL_GPL(cgroup_get_from_id);
@@ -6111,7 +6142,7 @@ int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
 		struct cgroup *cgrp;
 		int ssid, count = 0;
 
-		if (root == &cgrp_dfl_root && !cgrp_dfl_visible)
+		if (root == &cgrp_dfl_root && !READ_ONCE(cgrp_dfl_visible))
 			continue;
 
 		seq_printf(m, "%d:", root->hierarchy_id);
@@ -6653,8 +6684,12 @@ struct cgroup *cgroup_get_from_path(const char *path)
 {
 	struct kernfs_node *kn;
 	struct cgroup *cgrp = ERR_PTR(-ENOENT);
+	struct cgroup *root_cgrp;
 
-	kn = kernfs_walk_and_get(cgrp_dfl_root.cgrp.kn, path);
+	spin_lock_irq(&css_set_lock);
+	root_cgrp = current_cgns_cgroup_from_root(&cgrp_dfl_root);
+	kn = kernfs_walk_and_get(root_cgrp->kn, path);
+	spin_unlock_irq(&css_set_lock);
 	if (!kn)
 		goto out;
 
@@ -6812,9 +6847,6 @@ static ssize_t show_delegatable_files(struct cftype *files, char *buf,
 		if (!(cft->flags & CFTYPE_NS_DELEGATABLE))
 			continue;
 
-		if ((cft->flags & CFTYPE_PRESSURE) && !cgroup_psi_enabled())
-			continue;
-
 		if (prefix)
 			ret += snprintf(buf + ret, size - ret, "%s.", prefix);
 
@@ -6834,8 +6866,11 @@ static ssize_t delegate_show(struct kobject *kobj, struct kobj_attribute *attr,
 	int ssid;
 	ssize_t ret = 0;
 
-	ret = show_delegatable_files(cgroup_base_files, buf, PAGE_SIZE - ret,
-				     NULL);
+	ret = show_delegatable_files(cgroup_base_files, buf + ret,
+				     PAGE_SIZE - ret, NULL);
+	if (cgroup_psi_enabled())
+		ret += show_delegatable_files(cgroup_psi_files, buf + ret,
+					      PAGE_SIZE - ret, NULL);
 
 	for_each_subsys(ss, ssid)
 		ret += show_delegatable_files(ss->dfl_cftypes, buf + ret,
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 1f3a55297f39..b474289c15b8 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -33,6 +33,7 @@
 #include <linux/interrupt.h>
 #include <linux/kernel.h>
 #include <linux/kmod.h>
+#include <linux/kthread.h>
 #include <linux/list.h>
 #include <linux/mempolicy.h>
 #include <linux/mm.h>
@@ -85,6 +86,30 @@ struct fmeter {
 	spinlock_t lock;	/* guards read or write of above */
 };
 
+/*
+ * Invalid partition error code
+ */
+enum prs_errcode {
+	PERR_NONE = 0,
+	PERR_INVCPUS,
+	PERR_INVPARENT,
+	PERR_NOTPART,
+	PERR_NOTEXCL,
+	PERR_NOCPUS,
+	PERR_HOTPLUG,
+	PERR_CPUSEMPTY,
+};
+
+static const char * const perr_strings[] = {
+	[PERR_INVCPUS]   = "Invalid cpu list in cpuset.cpus",
+	[PERR_INVPARENT] = "Parent is an invalid partition root",
+	[PERR_NOTPART]   = "Parent is not a partition root",
+	[PERR_NOTEXCL]   = "Cpu list in cpuset.cpus not exclusive",
+	[PERR_NOCPUS]    = "Parent unable to distribute cpu downstream",
+	[PERR_HOTPLUG]   = "No cpu available due to hotplug",
+	[PERR_CPUSEMPTY] = "cpuset.cpus is empty",
+};
+
 struct cpuset {
 	struct cgroup_subsys_state css;
 
@@ -168,6 +193,9 @@ struct cpuset {
 	int use_parent_ecpus;
 	int child_ecpus_count;
 
+	/* Invalid partition error code, not lock protected */
+	enum prs_errcode prs_err;
+
 	/* Handle for cpuset.cpus.partition */
 	struct cgroup_file partition_file;
 };
@@ -175,20 +203,22 @@ struct cpuset {
 /*
  * Partition root states:
  *
- *   0 - not a partition root
- *
+ *   0 - member (not a partition root)
  *   1 - partition root
- *
+ *   2 - partition root without load balancing (isolated)
  *  -1 - invalid partition root
- *       None of the cpus in cpus_allowed can be put into the parent's
- *       subparts_cpus. In this case, the cpuset is not a real partition
- *       root anymore.  However, the CPU_EXCLUSIVE bit will still be set
- *       and the cpuset can be restored back to a partition root if the
- *       parent cpuset can give more CPUs back to this child cpuset.
+ *  -2 - invalid isolated partition root
  */
-#define PRS_DISABLED		0
-#define PRS_ENABLED		1
-#define PRS_ERROR		-1
+#define PRS_MEMBER		0
+#define PRS_ROOT		1
+#define PRS_ISOLATED		2
+#define PRS_INVALID_ROOT	-1
+#define PRS_INVALID_ISOLATED	-2
+
+static inline bool is_prs_invalid(int prs_state)
+{
+	return prs_state < 0;
+}
 
 /*
  * Temporary cpumasks for working with partitions that are passed among
@@ -268,25 +298,43 @@ static inline int is_spread_slab(const struct cpuset *cs)
 	return test_bit(CS_SPREAD_SLAB, &cs->flags);
 }
 
-static inline int is_partition_root(const struct cpuset *cs)
+static inline int is_partition_valid(const struct cpuset *cs)
 {
 	return cs->partition_root_state > 0;
 }
 
+static inline int is_partition_invalid(const struct cpuset *cs)
+{
+	return cs->partition_root_state < 0;
+}
+
+/*
+ * Callers should hold callback_lock to modify partition_root_state.
+ */
+static inline void make_partition_invalid(struct cpuset *cs)
+{
+	if (is_partition_valid(cs))
+		cs->partition_root_state = -cs->partition_root_state;
+}
+
 /*
  * Send notification event of whenever partition_root_state changes.
  */
-static inline void notify_partition_change(struct cpuset *cs,
-					   int old_prs, int new_prs)
+static inline void notify_partition_change(struct cpuset *cs, int old_prs)
 {
-	if (old_prs != new_prs)
-		cgroup_file_notify(&cs->partition_file);
+	if (old_prs == cs->partition_root_state)
+		return;
+	cgroup_file_notify(&cs->partition_file);
+
+	/* Reset prs_err if not invalid */
+	if (is_partition_valid(cs))
+		WRITE_ONCE(cs->prs_err, PERR_NONE);
 }
 
 static struct cpuset top_cpuset = {
 	.flags = ((1 << CS_ONLINE) | (1 << CS_CPU_EXCLUSIVE) |
 		  (1 << CS_MEM_EXCLUSIVE)),
-	.partition_root_state = PRS_ENABLED,
+	.partition_root_state = PRS_ROOT,
 };
 
 /**
@@ -404,6 +452,41 @@ static inline bool is_in_v2_mode(void)
 	      (cpuset_cgrp_subsys.root->flags & CGRP_ROOT_CPUSET_V2_MODE);
 }
 
+/**
+ * partition_is_populated - check if partition has tasks
+ * @cs: partition root to be checked
+ * @excluded_child: a child cpuset to be excluded in task checking
+ * Return: true if there are tasks, false otherwise
+ *
+ * It is assumed that @cs is a valid partition root. @excluded_child should
+ * be non-NULL when this cpuset is going to become a partition itself.
+ */
+static inline bool partition_is_populated(struct cpuset *cs,
+					  struct cpuset *excluded_child)
+{
+	struct cgroup_subsys_state *css;
+	struct cpuset *child;
+
+	if (cs->css.cgroup->nr_populated_csets)
+		return true;
+	if (!excluded_child && !cs->nr_subparts_cpus)
+		return cgroup_is_populated(cs->css.cgroup);
+
+	rcu_read_lock();
+	cpuset_for_each_child(child, css, cs) {
+		if (child == excluded_child)
+			continue;
+		if (is_partition_valid(child))
+			continue;
+		if (cgroup_is_populated(child->css.cgroup)) {
+			rcu_read_unlock();
+			return true;
+		}
+	}
+	rcu_read_unlock();
+	return false;
+}
+
 /*
  * Return in pmask the portion of a task's cpusets's cpus_allowed that
  * are online and are capable of running the task.  If none are found,
@@ -659,22 +742,6 @@ static int validate_change(struct cpuset *cur, struct cpuset *trial)
 	par = parent_cs(cur);
 
 	/*
-	 * If either I or some sibling (!= me) is exclusive, we can't
-	 * overlap
-	 */
-	ret = -EINVAL;
-	cpuset_for_each_child(c, css, par) {
-		if ((is_cpu_exclusive(trial) || is_cpu_exclusive(c)) &&
-		    c != cur &&
-		    cpumask_intersects(trial->cpus_allowed, c->cpus_allowed))
-			goto out;
-		if ((is_mem_exclusive(trial) || is_mem_exclusive(c)) &&
-		    c != cur &&
-		    nodes_intersects(trial->mems_allowed, c->mems_allowed))
-			goto out;
-	}
-
-	/*
 	 * Cpusets with tasks - existing or newly being attached - can't
 	 * be changed to have empty cpus_allowed or mems_allowed.
 	 */
@@ -698,6 +765,22 @@ static int validate_change(struct cpuset *cur, struct cpuset *trial)
 				       trial->cpus_allowed))
 		goto out;
 
+	/*
+	 * If either I or some sibling (!= me) is exclusive, we can't
+	 * overlap
+	 */
+	ret = -EINVAL;
+	cpuset_for_each_child(c, css, par) {
+		if ((is_cpu_exclusive(trial) || is_cpu_exclusive(c)) &&
+		    c != cur &&
+		    cpumask_intersects(trial->cpus_allowed, c->cpus_allowed))
+			goto out;
+		if ((is_mem_exclusive(trial) || is_mem_exclusive(c)) &&
+		    c != cur &&
+		    nodes_intersects(trial->mems_allowed, c->mems_allowed))
+			goto out;
+	}
+
 	ret = 0;
 out:
 	rcu_read_unlock();
@@ -875,7 +958,7 @@ static int generate_sched_domains(cpumask_var_t **domains,
 			csa[csn++] = cp;
 
 		/* skip @cp's subtree if not a partition root */
-		if (!is_partition_root(cp))
+		if (!is_partition_valid(cp))
 			pos_css = css_rightmost_descendant(pos_css);
 	}
 	rcu_read_unlock();
@@ -1081,7 +1164,7 @@ static void rebuild_sched_domains_locked(void)
 	if (top_cpuset.nr_subparts_cpus) {
 		rcu_read_lock();
 		cpuset_for_each_descendant_pre(cs, pos_css, &top_cpuset) {
-			if (!is_partition_root(cs)) {
+			if (!is_partition_valid(cs)) {
 				pos_css = css_rightmost_descendant(pos_css);
 				continue;
 			}
@@ -1127,10 +1210,18 @@ static void update_tasks_cpumask(struct cpuset *cs)
 {
 	struct css_task_iter it;
 	struct task_struct *task;
+	bool top_cs = cs == &top_cpuset;
 
 	css_task_iter_start(&cs->css, 0, &it);
-	while ((task = css_task_iter_next(&it)))
+	while ((task = css_task_iter_next(&it))) {
+		/*
+		 * Percpu kthreads in top_cpuset are ignored
+		 */
+		if (top_cs && (task->flags & PF_KTHREAD) &&
+		    kthread_is_per_cpu(task))
+			continue;
 		set_cpus_allowed_ptr(task, cs->effective_cpus);
+	}
 	css_task_iter_end(&it);
 }
 
@@ -1165,15 +1256,18 @@ enum subparts_cmd {
 	partcmd_enable,		/* Enable partition root	 */
 	partcmd_disable,	/* Disable partition root	 */
 	partcmd_update,		/* Update parent's subparts_cpus */
+	partcmd_invalidate,	/* Make partition invalid	 */
 };
 
+static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
+		       int turning_on);
 /**
  * update_parent_subparts_cpumask - update subparts_cpus mask of parent cpuset
  * @cpuset:  The cpuset that requests change in partition root state
  * @cmd:     Partition root state change command
  * @newmask: Optional new cpumask for partcmd_update
  * @tmp:     Temporary addmask and delmask
- * Return:   0, 1 or an error code
+ * Return:   0 or a partition root state error code
  *
  * For partcmd_enable, the cpuset is being transformed from a non-partition
  * root to a partition root. The cpus_allowed mask of the given cpuset will
@@ -1184,38 +1278,36 @@ enum subparts_cmd {
  * For partcmd_disable, the cpuset is being transformed from a partition
  * root back to a non-partition root. Any CPUs in cpus_allowed that are in
  * parent's subparts_cpus will be taken away from that cpumask and put back
- * into parent's effective_cpus. 0 should always be returned.
- *
- * For partcmd_update, if the optional newmask is specified, the cpu
- * list is to be changed from cpus_allowed to newmask. Otherwise,
- * cpus_allowed is assumed to remain the same. The cpuset should either
- * be a partition root or an invalid partition root. The partition root
- * state may change if newmask is NULL and none of the requested CPUs can
- * be granted by the parent. The function will return 1 if changes to
- * parent's subparts_cpus and effective_cpus happen or 0 otherwise.
- * Error code should only be returned when newmask is non-NULL.
+ * into parent's effective_cpus. 0 will always be returned.
  *
- * The partcmd_enable and partcmd_disable commands are used by
- * update_prstate(). The partcmd_update command is used by
- * update_cpumasks_hier() with newmask NULL and update_cpumask() with
- * newmask set.
+ * For partcmd_update, if the optional newmask is specified, the cpu list is
+ * to be changed from cpus_allowed to newmask. Otherwise, cpus_allowed is
+ * assumed to remain the same. The cpuset should either be a valid or invalid
+ * partition root. The partition root state may change from valid to invalid
+ * or vice versa. An error code will only be returned if transitioning from
+ * invalid to valid violates the exclusivity rule.
  *
- * The checking is more strict when enabling partition root than the
- * other two commands.
+ * For partcmd_invalidate, the current partition will be made invalid.
  *
- * Because of the implicit cpu exclusive nature of a partition root,
- * cpumask changes that violates the cpu exclusivity rule will not be
- * permitted when checked by validate_change().
+ * The partcmd_enable and partcmd_disable commands are used by
+ * update_prstate(). An error code may be returned and the caller will check
+ * for error.
+ *
+ * The partcmd_update command is used by update_cpumasks_hier() with newmask
+ * NULL and update_cpumask() with newmask set. The partcmd_invalidate is used
+ * by update_cpumask() with NULL newmask. In both cases, the callers won't
+ * check for error and so partition_root_state and prs_error will be updated
+ * directly.
  */
-static int update_parent_subparts_cpumask(struct cpuset *cpuset, int cmd,
+static int update_parent_subparts_cpumask(struct cpuset *cs, int cmd,
 					  struct cpumask *newmask,
 					  struct tmpmasks *tmp)
 {
-	struct cpuset *parent = parent_cs(cpuset);
+	struct cpuset *parent = parent_cs(cs);
 	int adding;	/* Moving cpus from effective_cpus to subparts_cpus */
 	int deleting;	/* Moving cpus from subparts_cpus to effective_cpus */
 	int old_prs, new_prs;
-	bool part_error = false;	/* Partition error? */
+	int part_error = PERR_NONE;	/* Partition error? */
 
 	percpu_rwsem_assert_held(&cpuset_rwsem);
 
@@ -1224,126 +1316,165 @@ static int update_parent_subparts_cpumask(struct cpuset *cpuset, int cmd,
 	 * The new cpumask, if present, or the current cpus_allowed must
 	 * not be empty.
 	 */
-	if (!is_partition_root(parent) ||
-	   (newmask && cpumask_empty(newmask)) ||
-	   (!newmask && cpumask_empty(cpuset->cpus_allowed)))
-		return -EINVAL;
-
-	/*
-	 * Enabling/disabling partition root is not allowed if there are
-	 * online children.
-	 */
-	if ((cmd != partcmd_update) && css_has_online_children(&cpuset->css))
-		return -EBUSY;
-
-	/*
-	 * Enabling partition root is not allowed if not all the CPUs
-	 * can be granted from parent's effective_cpus or at least one
-	 * CPU will be left after that.
-	 */
-	if ((cmd == partcmd_enable) &&
-	   (!cpumask_subset(cpuset->cpus_allowed, parent->effective_cpus) ||
-	     cpumask_equal(cpuset->cpus_allowed, parent->effective_cpus)))
-		return -EINVAL;
+	if (!is_partition_valid(parent)) {
+		return is_partition_invalid(parent)
+		       ? PERR_INVPARENT : PERR_NOTPART;
+	}
+	if ((newmask && cpumask_empty(newmask)) ||
+	   (!newmask && cpumask_empty(cs->cpus_allowed)))
+		return PERR_CPUSEMPTY;
 
 	/*
-	 * A cpumask update cannot make parent's effective_cpus become empty.
+	 * new_prs will only be changed for the partcmd_update and
+	 * partcmd_invalidate commands.
 	 */
 	adding = deleting = false;
-	old_prs = new_prs = cpuset->partition_root_state;
+	old_prs = new_prs = cs->partition_root_state;
 	if (cmd == partcmd_enable) {
-		cpumask_copy(tmp->addmask, cpuset->cpus_allowed);
+		/*
+		 * Enabling partition root is not allowed if cpus_allowed
+		 * doesn't overlap parent's cpus_allowed.
+		 */
+		if (!cpumask_intersects(cs->cpus_allowed, parent->cpus_allowed))
+			return PERR_INVCPUS;
+
+		/*
+		 * A parent can be left with no CPU as long as there is no
+		 * task directly associated with the parent partition.
+		 */
+		if (!cpumask_intersects(cs->cpus_allowed, parent->effective_cpus) &&
+		    partition_is_populated(parent, cs))
+			return PERR_NOCPUS;
+
+		cpumask_copy(tmp->addmask, cs->cpus_allowed);
 		adding = true;
 	} else if (cmd == partcmd_disable) {
-		deleting = cpumask_and(tmp->delmask, cpuset->cpus_allowed,
+		/*
+		 * Need to remove cpus from parent's subparts_cpus for valid
+		 * partition root.
+		 */
+		deleting = !is_prs_invalid(old_prs) &&
+			   cpumask_and(tmp->delmask, cs->cpus_allowed,
+				       parent->subparts_cpus);
+	} else if (cmd == partcmd_invalidate) {
+		if (is_prs_invalid(old_prs))
+			return 0;
+
+		/*
+		 * Make the current partition invalid. It is assumed that
+		 * invalidation is caused by violating cpu exclusivity rule.
+		 */
+		deleting = cpumask_and(tmp->delmask, cs->cpus_allowed,
 				       parent->subparts_cpus);
+		if (old_prs > 0) {
+			new_prs = -old_prs;
+			part_error = PERR_NOTEXCL;
+		}
 	} else if (newmask) {
 		/*
 		 * partcmd_update with newmask:
 		 *
+		 * Compute add/delete mask to/from subparts_cpus
+		 *
 		 * delmask = cpus_allowed & ~newmask & parent->subparts_cpus
-		 * addmask = newmask & parent->effective_cpus
+		 * addmask = newmask & parent->cpus_allowed
 		 *		     & ~parent->subparts_cpus
 		 */
-		cpumask_andnot(tmp->delmask, cpuset->cpus_allowed, newmask);
+		cpumask_andnot(tmp->delmask, cs->cpus_allowed, newmask);
 		deleting = cpumask_and(tmp->delmask, tmp->delmask,
 				       parent->subparts_cpus);
 
-		cpumask_and(tmp->addmask, newmask, parent->effective_cpus);
+		cpumask_and(tmp->addmask, newmask, parent->cpus_allowed);
 		adding = cpumask_andnot(tmp->addmask, tmp->addmask,
 					parent->subparts_cpus);
 		/*
-		 * Return error if the new effective_cpus could become empty.
+		 * Make partition invalid if parent's effective_cpus could
+		 * become empty and there are tasks in the parent.
 		 */
 		if (adding &&
-		    cpumask_equal(parent->effective_cpus, tmp->addmask)) {
-			if (!deleting)
-				return -EINVAL;
-			/*
-			 * As some of the CPUs in subparts_cpus might have
-			 * been offlined, we need to compute the real delmask
-			 * to confirm that.
-			 */
-			if (!cpumask_and(tmp->addmask, tmp->delmask,
-					 cpu_active_mask))
-				return -EINVAL;
-			cpumask_copy(tmp->addmask, parent->effective_cpus);
+		    cpumask_subset(parent->effective_cpus, tmp->addmask) &&
+		    !cpumask_intersects(tmp->delmask, cpu_active_mask) &&
+		    partition_is_populated(parent, cs)) {
+			part_error = PERR_NOCPUS;
+			adding = false;
+			deleting = cpumask_and(tmp->delmask, cs->cpus_allowed,
+					       parent->subparts_cpus);
 		}
 	} else {
 		/*
 		 * partcmd_update w/o newmask:
 		 *
-		 * addmask = cpus_allowed & parent->effective_cpus
+		 * delmask = cpus_allowed & parent->subparts_cpus
+		 * addmask = cpus_allowed & parent->cpus_allowed
+		 *			  & ~parent->subparts_cpus
 		 *
-		 * Note that parent's subparts_cpus may have been
-		 * pre-shrunk in case there is a change in the cpu list.
-		 * So no deletion is needed.
+		 * This gets invoked either due to a hotplug event or from
+		 * update_cpumasks_hier(). This can cause the state of a
+		 * partition root to transition from valid to invalid or vice
+		 * versa. So we still need to compute the addmask and delmask.
+
+		 * A partition error happens when:
+		 * 1) Cpuset is valid partition, but parent does not distribute
+		 *    out any CPUs.
+		 * 2) Parent has tasks and all its effective CPUs will have
+		 *    to be distributed out.
 		 */
-		adding = cpumask_and(tmp->addmask, cpuset->cpus_allowed,
-				     parent->effective_cpus);
-		part_error = cpumask_equal(tmp->addmask,
-					   parent->effective_cpus);
+		cpumask_and(tmp->addmask, cs->cpus_allowed,
+					  parent->cpus_allowed);
+		adding = cpumask_andnot(tmp->addmask, tmp->addmask,
+					parent->subparts_cpus);
+
+		if ((is_partition_valid(cs) && !parent->nr_subparts_cpus) ||
+		    (adding &&
+		     cpumask_subset(parent->effective_cpus, tmp->addmask) &&
+		     partition_is_populated(parent, cs))) {
+			part_error = PERR_NOCPUS;
+			adding = false;
+		}
+
+		if (part_error && is_partition_valid(cs) &&
+		    parent->nr_subparts_cpus)
+			deleting = cpumask_and(tmp->delmask, cs->cpus_allowed,
+					       parent->subparts_cpus);
 	}
+	if (part_error)
+		WRITE_ONCE(cs->prs_err, part_error);
 
 	if (cmd == partcmd_update) {
-		int prev_prs = cpuset->partition_root_state;
-
 		/*
-		 * Check for possible transition between PRS_ENABLED
-		 * and PRS_ERROR.
+		 * Check for possible transition between valid and invalid
+		 * partition root.
 		 */
-		switch (cpuset->partition_root_state) {
-		case PRS_ENABLED:
+		switch (cs->partition_root_state) {
+		case PRS_ROOT:
+		case PRS_ISOLATED:
 			if (part_error)
-				new_prs = PRS_ERROR;
+				new_prs = -old_prs;
 			break;
-		case PRS_ERROR:
+		case PRS_INVALID_ROOT:
+		case PRS_INVALID_ISOLATED:
 			if (!part_error)
-				new_prs = PRS_ENABLED;
+				new_prs = -old_prs;
 			break;
 		}
-		/*
-		 * Set part_error if previously in invalid state.
-		 */
-		part_error = (prev_prs == PRS_ERROR);
-	}
-
-	if (!part_error && (new_prs == PRS_ERROR))
-		return 0;	/* Nothing need to be done */
-
-	if (new_prs == PRS_ERROR) {
-		/*
-		 * Remove all its cpus from parent's subparts_cpus.
-		 */