Merge tag 'cgroup-for-6.8' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Pull cgroup updates from Tejun Heo:

 - Yafang Shao added task_get_cgroup1() helper to enable a similar BPF
   helper so that BPF progs can be more useful on cgroup1 hierarchies.
   While cgroup1 is mostly in maintenance mode, this addition is very
   small while having an outsized usefulness for users who are still on
   cgroup1. Yafang also optimized root cgroup list access by making it
   RCU protected in the process.

 - Waiman Long optimized rstat operation leading to substantially lower
   and more consistent lock hold time while flushing the hierarchical
   statistics. As the lock can be acquired briefly in various hot paths,
   this reduction has cascading benefits.

 - Waiman also improved the quality of isolation for cpuset's isolated
   partitions. CPUs which are allocated to isolated partitions are now
   excluded from running unbound work items and cpu_is_isolated() test
   which is used by vmstat and memcg to reduce interference now includes
   cpuset isolated CPUs. While it isn't there yet, the hope is
   eventually reaching parity with the isolation level provided by the
   `isolcpus` boot param but in a dynamic manner.

* tag 'cgroup-for-6.8' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroup: Move rcu_head up near the top of cgroup_root
  cgroup/cpuset: Include isolated cpuset CPUs in cpu_is_isolated() check
  cgroup: Avoid false cacheline sharing of read mostly rstat_cpu
  cgroup/rstat: Optimize cgroup_rstat_updated_list()
  cgroup: Fix documentation for cpu.idle
  cgroup/cpuset: Expose cpuset.cpus.isolated
  workqueue: Move workqueue_set_unbound_cpumask() and its helpers inside CONFIG_SYSFS
  cgroup/rstat: Reduce cpu_lock hold time in cgroup_rstat_flush_locked()
  cgroup/cpuset: Take isolated CPUs out of workqueue unbound cpumask
  cgroup/cpuset: Keep track of CPUs in isolated partitions
  selftests/cgroup: Minor code cleanup and reorganization of test_cpuset_prs.sh
  workqueue: Add workqueue_unbound_exclude_cpumask() to exclude CPUs from wq_unbound_cpumask
  selftests: cgroup: Fixes a typo in a comment
  cgroup: Add a new helper for cgroup1 hierarchy
  cgroup: Add annotation for holding namespace_sem in current_cgns_cgroup_from_root()
  cgroup: Eliminate the need for cgroup_mutex in proc_cgroup_show()
  cgroup: Make operations on the cgroup root_list RCU safe
  cgroup: Remove unnecessary list_empty()

1 files changed, 224 insertions, 73 deletions

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 615daaf87f1f..dfbb16aca9f4 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -25,6 +25,7 @@
 #include <linux/cpu.h>
 #include <linux/cpumask.h>
 #include <linux/cpuset.h>
+#include <linux/delay.h>
 #include <linux/init.h>
 #include <linux/interrupt.h>
 #include <linux/kernel.h>
@@ -43,6 +44,7 @@
 #include <linux/sched/isolation.h>
 #include <linux/cgroup.h>
 #include <linux/wait.h>
+#include <linux/workqueue.h>
 
 DEFINE_STATIC_KEY_FALSE(cpusets_pre_enable_key);
 DEFINE_STATIC_KEY_FALSE(cpusets_enabled_key);
@@ -204,6 +206,11 @@ struct cpuset {
  */
 static cpumask_var_t	subpartitions_cpus;
 
+/*
+ * Exclusive CPUs in isolated partitions
+ */
+static cpumask_var_t	isolated_cpus;
+
 /* List of remote partition root children */
 static struct list_head remote_children;
 
@@ -1317,6 +1324,7 @@ static void compute_effective_cpumask(struct cpumask *new_cpus,
  */
 enum partition_cmd {
 	partcmd_enable,		/* Enable partition root	  */
+	partcmd_enablei,	/* Enable isolated partition root */
 	partcmd_disable,	/* Disable partition root	  */
 	partcmd_update,		/* Update parent's effective_cpus */
 	partcmd_invalidate,	/* Make partition invalid	  */
@@ -1419,6 +1427,109 @@ static void reset_partition_data(struct cpuset *cs)
 }
 
 /*
+ * partition_xcpus_newstate - Exclusive CPUs state change
+ * @old_prs: old partition_root_state
+ * @new_prs: new partition_root_state
+ * @xcpus: exclusive CPUs with state change
+ */
+static void partition_xcpus_newstate(int old_prs, int new_prs, struct cpumask *xcpus)
+{
+	WARN_ON_ONCE(old_prs == new_prs);
+	if (new_prs == PRS_ISOLATED)
+		cpumask_or(isolated_cpus, isolated_cpus, xcpus);
+	else
+		cpumask_andnot(isolated_cpus, isolated_cpus, xcpus);
+}
+
+/*
+ * partition_xcpus_add - Add new exclusive CPUs to partition
+ * @new_prs: new partition_root_state
+ * @parent: parent cpuset
+ * @xcpus: exclusive CPUs to be added
+ * Return: true if isolated_cpus modified, false otherwise
+ *
+ * Remote partition if parent == NULL
+ */
+static bool partition_xcpus_add(int new_prs, struct cpuset *parent,
+				struct cpumask *xcpus)
+{
+	bool isolcpus_updated;
+
+	WARN_ON_ONCE(new_prs < 0);
+	lockdep_assert_held(&callback_lock);
+	if (!parent)
+		parent = &top_cpuset;
+
+
+	if (parent == &top_cpuset)
+		cpumask_or(subpartitions_cpus, subpartitions_cpus, xcpus);
+
+	isolcpus_updated = (new_prs != parent->partition_root_state);
+	if (isolcpus_updated)
+		partition_xcpus_newstate(parent->partition_root_state, new_prs,
+					 xcpus);
+
+	cpumask_andnot(parent->effective_cpus, parent->effective_cpus, xcpus);
+	return isolcpus_updated;
+}
+
+/*
+ * partition_xcpus_del - Remove exclusive CPUs from partition
+ * @old_prs: old partition_root_state
+ * @parent: parent cpuset
+ * @xcpus: exclusive CPUs to be removed
+ * Return: true if isolated_cpus modified, false otherwise
+ *
+ * Remote partition if parent == NULL
+ */
+static bool partition_xcpus_del(int old_prs, struct cpuset *parent,
+				struct cpumask *xcpus)
+{
+	bool isolcpus_updated;
+
+	WARN_ON_ONCE(old_prs < 0);
+	lockdep_assert_held(&callback_lock);
+	if (!parent)
+		parent = &top_cpuset;
+
+	if (parent == &top_cpuset)
+		cpumask_andnot(subpartitions_cpus, subpartitions_cpus, xcpus);
+
+	isolcpus_updated = (old_prs != parent->partition_root_state);
+	if (isolcpus_updated)
+		partition_xcpus_newstate(old_prs, parent->partition_root_state,
+					 xcpus);
+
+	cpumask_and(xcpus, xcpus, cpu_active_mask);
+	cpumask_or(parent->effective_cpus, parent->effective_cpus, xcpus);
+	return isolcpus_updated;
+}
+
+static void update_unbound_workqueue_cpumask(bool isolcpus_updated)
+{
+	int ret;
+
+	lockdep_assert_cpus_held();
+
+	if (!isolcpus_updated)
+		return;
+
+	ret = workqueue_unbound_exclude_cpumask(isolated_cpus);
+	WARN_ON_ONCE(ret < 0);
+}
+
+/**
+ * cpuset_cpu_is_isolated - Check if the given CPU is isolated
+ * @cpu: the CPU number to be checked
+ * Return: true if CPU is used in an isolated partition, false otherwise
+ */
+bool cpuset_cpu_is_isolated(int cpu)
+{
+	return cpumask_test_cpu(cpu, isolated_cpus);
+}
+EXPORT_SYMBOL_GPL(cpuset_cpu_is_isolated);
+
+/*
  * compute_effective_exclusive_cpumask - compute effective exclusive CPUs
  * @cs: cpuset
  * @xcpus: effective exclusive CPUs value to be set
@@ -1456,14 +1567,18 @@ static inline bool is_local_partition(struct cpuset *cs)
 /*
  * remote_partition_enable - Enable current cpuset as a remote partition root
  * @cs: the cpuset to update
+ * @new_prs: new partition_root_state
  * @tmp: temparary masks
  * Return: 1 if successful, 0 if error
  *
  * Enable the current cpuset to become a remote partition root taking CPUs
  * directly from the top cpuset. cpuset_mutex must be held by the caller.
  */
-static int remote_partition_enable(struct cpuset *cs, struct tmpmasks *tmp)
+static int remote_partition_enable(struct cpuset *cs, int new_prs,
+				   struct tmpmasks *tmp)
 {
+	bool isolcpus_updated;
+
 	/*
 	 * The user must have sysadmin privilege.
 	 */
@@ -1485,26 +1600,22 @@ static int remote_partition_enable(struct cpuset *cs, struct tmpmasks *tmp)
 		return 0;
 
 	spin_lock_irq(&callback_lock);
-	cpumask_andnot(top_cpuset.effective_cpus,
-		       top_cpuset.effective_cpus, tmp->new_cpus);
-	cpumask_or(subpartitions_cpus,
-		   subpartitions_cpus, tmp->new_cpus);
-
+	isolcpus_updated = partition_xcpus_add(new_prs, NULL, tmp->new_cpus);
+	list_add(&cs->remote_sibling, &remote_children);
 	if (cs->use_parent_ecpus) {
 		struct cpuset *parent = parent_cs(cs);
 
 		cs->use_parent_ecpus = false;
 		parent->child_ecpus_count--;
 	}
-	list_add(&cs->remote_sibling, &remote_children);
 	spin_unlock_irq(&callback_lock);
+	update_unbound_workqueue_cpumask(isolcpus_updated);
 
 	/*
 	 * Proprogate changes in top_cpuset's effective_cpus down the hierarchy.
 	 */
 	update_tasks_cpumask(&top_cpuset, tmp->new_cpus);
 	update_sibling_cpumasks(&top_cpuset, NULL, tmp);
-
 	return 1;
 }
 
@@ -1519,23 +1630,22 @@ static int remote_partition_enable(struct cpuset *cs, struct tmpmasks *tmp)
  */
 static void remote_partition_disable(struct cpuset *cs, struct tmpmasks *tmp)
 {
+	bool isolcpus_updated;
+
 	compute_effective_exclusive_cpumask(cs, tmp->new_cpus);
 	WARN_ON_ONCE(!is_remote_partition(cs));
 	WARN_ON_ONCE(!cpumask_subset(tmp->new_cpus, subpartitions_cpus));
 
 	spin_lock_irq(&callback_lock);
-	cpumask_andnot(subpartitions_cpus,
-		       subpartitions_cpus, tmp->new_cpus);
-	cpumask_and(tmp->new_cpus,
-		    tmp->new_cpus, cpu_active_mask);
-	cpumask_or(top_cpuset.effective_cpus,
-		   top_cpuset.effective_cpus, tmp->new_cpus);
 	list_del_init(&cs->remote_sibling);
+	isolcpus_updated = partition_xcpus_del(cs->partition_root_state,
+					       NULL, tmp->new_cpus);
 	cs->partition_root_state = -cs->partition_root_state;
 	if (!cs->prs_err)
 		cs->prs_err = PERR_INVCPUS;
 	reset_partition_data(cs);
 	spin_unlock_irq(&callback_lock);
+	update_unbound_workqueue_cpumask(isolcpus_updated);
 
 	/*
 	 * Proprogate changes in top_cpuset's effective_cpus down the hierarchy.
@@ -1557,6 +1667,8 @@ static void remote_cpus_update(struct cpuset *cs, struct cpumask *newmask,
 			       struct tmpmasks *tmp)
 {
 	bool adding, deleting;
+	int prs = cs->partition_root_state;
+	int isolcpus_updated = 0;
 
 	if (WARN_ON_ONCE(!is_remote_partition(cs)))
 		return;
@@ -1580,21 +1692,12 @@ static void remote_cpus_update(struct cpuset *cs, struct cpumask *newmask,
 		goto invalidate;
 
 	spin_lock_irq(&callback_lock);
-	if (adding) {
-		cpumask_or(subpartitions_cpus,
-			   subpartitions_cpus, tmp->addmask);
-		cpumask_andnot(top_cpuset.effective_cpus,
-			       top_cpuset.effective_cpus, tmp->addmask);
-	}
-	if (deleting) {
-		cpumask_andnot(subpartitions_cpus,
-			       subpartitions_cpus, tmp->delmask);
-		cpumask_and(tmp->delmask,
-			    tmp->delmask, cpu_active_mask);
-		cpumask_or(top_cpuset.effective_cpus,
-			   top_cpuset.effective_cpus, tmp->delmask);
-	}
+	if (adding)
+		isolcpus_updated += partition_xcpus_add(prs, NULL, tmp->addmask);
+	if (deleting)
+		isolcpus_updated += partition_xcpus_del(prs, NULL, tmp->delmask);
 	spin_unlock_irq(&callback_lock);
+	update_unbound_workqueue_cpumask(isolcpus_updated);
 
 	/*
 	 * Proprogate changes in top_cpuset's effective_cpus down the hierarchy.
@@ -1676,11 +1779,11 @@ static bool prstate_housekeeping_conflict(int prstate, struct cpumask *new_cpus)
  * @tmp:     Temporary addmask and delmask
  * 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 effective_xcpus (cpus_allowed if effective_xcpus
- * not set) mask of the given cpuset will be taken away from parent's
- * effective_cpus. The function will return 0 if all the CPUs listed in
- * effective_xcpus can be granted or an error code will be returned.
+ * For partcmd_enable*, the cpuset is being transformed from a non-partition
+ * root to a partition root. The effective_xcpus (cpus_allowed if
+ * effective_xcpus not set) mask of the given cpuset will be taken away from
+ * parent's effective_cpus. The function will return 0 if all the CPUs listed
+ * in effective_xcpus can be granted or an error code will be returned.
  *
  * For partcmd_disable, the cpuset is being transformed from a partition
  * root back to a non-partition root. Any CPUs in effective_xcpus will be
@@ -1695,7 +1798,7 @@ static bool prstate_housekeeping_conflict(int prstate, struct cpumask *new_cpus)
  *
  * For partcmd_invalidate, the current partition will be made invalid.
  *
- * The partcmd_enable and partcmd_disable commands are used by
+ * 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.
  *
@@ -1716,6 +1819,7 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
 	int part_error = PERR_NONE;	/* Partition error? */
 	int subparts_delta = 0;
 	struct cpumask *xcpus;		/* cs effective_xcpus */
+	int isolcpus_updated = 0;
 	bool nocpu;
 
 	lockdep_assert_held(&cpuset_mutex);
@@ -1760,7 +1864,7 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
 
 	nocpu = tasks_nocpu_error(parent, cs, xcpus);
 
-	if (cmd == partcmd_enable) {
+	if ((cmd == partcmd_enable) || (cmd == partcmd_enablei)) {
 		/*
 		 * Enabling partition root is not allowed if its
 		 * effective_xcpus is empty or doesn't overlap with
@@ -1783,6 +1887,7 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
 		cpumask_copy(tmp->delmask, xcpus);
 		deleting = true;
 		subparts_delta++;
+		new_prs = (cmd == partcmd_enable) ? PRS_ROOT : PRS_ISOLATED;
 	} else if (cmd == partcmd_disable) {
 		/*
 		 * May need to add cpus to parent's effective_cpus for
@@ -1792,6 +1897,7 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
 			  cpumask_and(tmp->addmask, xcpus, parent->effective_xcpus);
 		if (adding)
 			subparts_delta--;
+		new_prs = PRS_MEMBER;
 	} else if (newmask) {
 		/*
 		 * Empty cpumask is not allowed
@@ -1940,38 +2046,28 @@ write_error:
 	 * newly deleted ones will be added back to effective_cpus.
 	 */
 	spin_lock_irq(&callback_lock);
-	if (adding) {
-		if (parent == &top_cpuset)
-			cpumask_andnot(subpartitions_cpus,
-				       subpartitions_cpus, tmp->addmask);
-		/*
-		 * Some of the CPUs in effective_xcpus might have been offlined.
-		 */
-		cpumask_or(parent->effective_cpus,
-			   parent->effective_cpus, tmp->addmask);
-		cpumask_and(parent->effective_cpus,
-			    parent->effective_cpus, cpu_active_mask);
-	}
-	if (deleting) {
-		if (parent == &top_cpuset)
-			cpumask_or(subpartitions_cpus,
-				   subpartitions_cpus, tmp->delmask);
-		cpumask_andnot(parent->effective_cpus,
-			       parent->effective_cpus, tmp->delmask);
-	}
-
-	if (is_partition_valid(parent)) {
-		parent->nr_subparts += subparts_delta;
-		WARN_ON_ONCE(parent->nr_subparts < 0);
-	}
-
 	if (old_prs != new_prs) {
 		cs->partition_root_state = new_prs;
 		if (new_prs <= 0)
 			cs->nr_subparts = 0;
 	}
+	/*
+	 * Adding to parent's effective_cpus means deletion CPUs from cs
+	 * and vice versa.
+	 */
+	if (adding)
+		isolcpus_updated += partition_xcpus_del(old_prs, parent,
+							tmp->addmask);
+	if (deleting)
+		isolcpus_updated += partition_xcpus_add(new_prs, parent,
+							tmp->delmask);
 
+	if (is_partition_valid(parent)) {
+		parent->nr_subparts += subparts_delta;
+		WARN_ON_ONCE(parent->nr_subparts < 0);
+	}
 	spin_unlock_irq(&callback_lock);
+	update_unbound_workqueue_cpumask(isolcpus_updated);
 
 	if ((old_prs != new_prs) && (cmd == partcmd_update))
 		update_partition_exclusive(cs, new_prs);
@@ -2948,6 +3044,7 @@ static int update_prstate(struct cpuset *cs, int new_prs)
 	int err = PERR_NONE, old_prs = cs->partition_root_state;
 	struct cpuset *parent = parent_cs(cs);
 	struct tmpmasks tmpmask;
+	bool new_xcpus_state = false;
 
 	if (old_prs == new_prs)
 		return 0;
@@ -2977,6 +3074,9 @@ static int update_prstate(struct cpuset *cs, int new_prs)
 		goto out;
 
 	if (!old_prs) {
+		enum partition_cmd cmd = (new_prs == PRS_ROOT)
+				       ? partcmd_enable : partcmd_enablei;
+
 		/*
 		 * cpus_allowed cannot be empty.
 		 */
@@ -2985,19 +3085,18 @@ static int update_prstate(struct cpuset *cs, int new_prs)
 			goto out;
 		}
 
-		err = update_parent_effective_cpumask(cs, partcmd_enable,
-						      NULL, &tmpmask);
+		err = update_parent_effective_cpumask(cs, cmd, NULL, &tmpmask);
 		/*
 		 * If an attempt to become local partition root fails,
 		 * try to become a remote partition root instead.
 		 */
-		if (err && remote_partition_enable(cs, &tmpmask))
+		if (err && remote_partition_enable(cs, new_prs, &tmpmask))
 			err = 0;
 	} else if (old_prs && new_prs) {
 		/*
 		 * A change in load balance state only, no change in cpumasks.
 		 */
-		;
+		new_xcpus_state = true;
 	} else {
 		/*
 		 * Switching back to member is always allowed even if it
@@ -3029,7 +3128,10 @@ out:
 	WRITE_ONCE(cs->prs_err, err);
 	if (!is_partition_valid(cs))
 		reset_partition_data(cs);
+	else if (new_xcpus_state)
+		partition_xcpus_newstate(old_prs, new_prs, cs->effective_xcpus);
 	spin_unlock_irq(&callback_lock);
+	update_unbound_workqueue_cpumask(new_xcpus_state);
 
 	/* Force update if switching back to member */
 	update_cpumasks_hier(cs, &tmpmask, !new_prs ? HIER_CHECKALL : 0);
@@ -3386,6 +3488,7 @@ typedef enum {
 	FILE_SUBPARTS_CPULIST,
 	FILE_EXCLUSIVE_CPULIST,
 	FILE_EFFECTIVE_XCPULIST,
+	FILE_ISOLATED_CPULIST,
 	FILE_CPU_EXCLUSIVE,
 	FILE_MEM_EXCLUSIVE,
 	FILE_MEM_HARDWALL,
@@ -3582,6 +3685,9 @@ static int cpuset_common_seq_show(struct seq_file *sf, void *v)
 	case FILE_SUBPARTS_CPULIST:
 		seq_printf(sf, "%*pbl\n", cpumask_pr_args(subpartitions_cpus));
 		break;
+	case FILE_ISOLATED_CPULIST:
+		seq_printf(sf, "%*pbl\n", cpumask_pr_args(isolated_cpus));
+		break;
 	default:
 		ret = -EINVAL;
 	}
@@ -3875,6 +3981,13 @@ static struct cftype dfl_files[] = {
 		.flags = CFTYPE_ONLY_ON_ROOT | CFTYPE_DEBUG,
 	},
 
+	{
+		.name = "cpus.isolated",
+		.seq_show = cpuset_common_seq_show,
+		.private = FILE_ISOLATED_CPULIST,
+		.flags = CFTYPE_ONLY_ON_ROOT,
+	},
+
 	{ }	/* terminate */
 };
 
@@ -4194,6 +4307,7 @@ int __init cpuset_init(void)
 	BUG_ON(!alloc_cpumask_var(&top_cpuset.effective_xcpus, GFP_KERNEL));
 	BUG_ON(!alloc_cpumask_var(&top_cpuset.exclusive_cpus, GFP_KERNEL));
 	BUG_ON(!zalloc_cpumask_var(&subpartitions_cpus, GFP_KERNEL));
+	BUG_ON(!zalloc_cpumask_var(&isolated_cpus, GFP_KERNEL));
 
 	cpumask_setall(top_cpuset.cpus_allowed);
 	nodes_setall(top_cpuset.mems_allowed);
@@ -4306,6 +4420,30 @@ void cpuset_force_rebuild(void)
 	force_rebuild = true;
 }
 
+/*
+ * Attempt to acquire a cpus_read_lock while a hotplug operation may be in
+ * progress.
+ * Return: true if successful, false otherwise
+ *
+ * To avoid circular lock dependency between cpuset_mutex and cpus_read_lock,
+ * cpus_read_trylock() is used here to acquire the lock.
+ */
+static bool cpuset_hotplug_cpus_read_trylock(void)
+{
+	int retries = 0;
+
+	while (!cpus_read_trylock()) {
+		/*
+		 * CPU hotplug still in progress. Retry 5 times
+		 * with a 10ms wait before bailing out.
+		 */
+		if (++retries > 5)
+			return false;
+		msleep(10);
+	}
+	return true;
+}
+
 /**
  * cpuset_hotplug_update_tasks - update tasks in a cpuset for hotunplug
  * @cs: cpuset in interest
@@ -4322,6 +4460,7 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
 	bool cpus_updated;
 	bool mems_updated;
 	bool remote;
+	int partcmd = -1;
 	struct cpuset *parent;
 retry:
 	wait_event(cpuset_attach_wq, cs->attach_in_progress == 0);
@@ -4353,11 +4492,13 @@ retry:
 		compute_partition_effective_cpumask(cs, &new_cpus);
 
 	if (remote && cpumask_empty(&new_cpus) &&
-	    partition_is_populated(cs, NULL)) {
+	    partition_is_populated(cs, NULL) &&
+	    cpuset_hotplug_cpus_read_trylock()) {
 		remote_partition_disable(cs, tmp);
 		compute_effective_cpumask(&new_cpus, cs, parent);
 		remote = false;
 		cpuset_force_rebuild();
+		cpus_read_unlock();
 	}
 
 	/*
@@ -4368,18 +4509,28 @@ retry:
 	 *    partitions.
 	 */
 	if (is_local_partition(cs) && (!is_partition_valid(parent) ||
-				tasks_nocpu_error(parent, cs, &new_cpus))) {
-		update_parent_effective_cpumask(cs, partcmd_invalidate, NULL, tmp);
-		compute_effective_cpumask(&new_cpus, cs, parent);
-		cpuset_force_rebuild();
-	}
+				tasks_nocpu_error(parent, cs, &new_cpus)))
+		partcmd = partcmd_invalidate;
 	/*
 	 * On the other hand, an invalid partition root may be transitioned
 	 * back to a regular one.
 	 */
-	else if (is_partition_valid(parent) && is_partition_invalid(cs)) {
-		update_parent_effective_cpumask(cs, partcmd_update, NULL, tmp);
-		if (is_partition_valid(cs)) {
+	else if (is_partition_valid(parent) && is_partition_invalid(cs))
+		partcmd = partcmd_update;
+
+	/*
+	 * cpus_read_lock needs to be held before calling
+	 * update_parent_effective_cpumask(). To avoid circular lock
+	 * dependency between cpuset_mutex and cpus_read_lock,
+	 * cpus_read_trylock() is used here to acquire the lock.
+	 */
+	if (partcmd >= 0) {
+		if (!cpuset_hotplug_cpus_read_trylock())
+			goto update_tasks;
+
+		update_parent_effective_cpumask(cs, partcmd, NULL, tmp);
+		cpus_read_unlock();
+		if ((partcmd == partcmd_invalidate) || is_partition_valid(cs)) {
 			compute_partition_effective_cpumask(cs, &new_cpus);
 			cpuset_force_rebuild();
 		}