Merge tag 'cpu-hotplug-3.15-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm

Pull CPU hotplug notifiers registration fixes from Rafael Wysocki:
 "The purpose of this single series of commits from Srivatsa S Bhat
  (with a small piece from Gautham R Shenoy) touching multiple
  subsystems that use CPU hotplug notifiers is to provide a way to
  register them that will not lead to deadlocks with CPU online/offline
  operations as described in the changelog of commit 93ae4f978ca7f ("CPU
  hotplug: Provide lockless versions of callback registration
  functions").

  The first three commits in the series introduce the API and document
  it and the rest simply goes through the users of CPU hotplug notifiers
  and converts them to using the new method"

* tag 'cpu-hotplug-3.15-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm: (52 commits)
  net/iucv/iucv.c: Fix CPU hotplug callback registration
  net/core/flow.c: Fix CPU hotplug callback registration
  mm, zswap: Fix CPU hotplug callback registration
  mm, vmstat: Fix CPU hotplug callback registration
  profile: Fix CPU hotplug callback registration
  trace, ring-buffer: Fix CPU hotplug callback registration
  xen, balloon: Fix CPU hotplug callback registration
  hwmon, via-cputemp: Fix CPU hotplug callback registration
  hwmon, coretemp: Fix CPU hotplug callback registration
  thermal, x86-pkg-temp: Fix CPU hotplug callback registration
  octeon, watchdog: Fix CPU hotplug callback registration
  oprofile, nmi-timer: Fix CPU hotplug callback registration
  intel-idle: Fix CPU hotplug callback registration
  clocksource, dummy-timer: Fix CPU hotplug callback registration
  drivers/base/topology.c: Fix CPU hotplug callback registration
  acpi-cpufreq: Fix CPU hotplug callback registration
  zsmalloc: Fix CPU hotplug callback registration
  scsi, fcoe: Fix CPU hotplug callback registration
  scsi, bnx2fc: Fix CPU hotplug callback registration
  scsi, bnx2i: Fix CPU hotplug callback registration
  ...

14 files changed, 138 insertions, 65 deletions

diff --git a/drivers/base/topology.c b/drivers/base/topology.c
index ad9d17762664..bbcbd3c43926 100644
--- a/drivers/base/topology.c
+++ b/drivers/base/topology.c
@@ -160,16 +160,20 @@ static int topology_cpu_callback(struct notifier_block *nfb,
 static int topology_sysfs_init(void)
 {
 	int cpu;
-	int rc;
+	int rc = 0;
+
+	cpu_notifier_register_begin();
 
 	for_each_online_cpu(cpu) {
 		rc = topology_add_dev(cpu);
 		if (rc)
-			return rc;
+			goto out;
 	}
-	hotcpu_notifier(topology_cpu_callback, 0);
+	__hotcpu_notifier(topology_cpu_callback, 0);
 
-	return 0;
+out:
+	cpu_notifier_register_done();
+	return rc;
 }
 
 device_initcall(topology_sysfs_init);
diff --git a/drivers/clocksource/dummy_timer.c b/drivers/clocksource/dummy_timer.c
index b3eb582d6a6f..ad3572541728 100644
--- a/drivers/clocksource/dummy_timer.c
+++ b/drivers/clocksource/dummy_timer.c
@@ -56,14 +56,19 @@ static struct notifier_block dummy_timer_cpu_nb = {
 
 static int __init dummy_timer_register(void)
 {
-	int err = register_cpu_notifier(&dummy_timer_cpu_nb);
+	int err = 0;
+
+	cpu_notifier_register_begin();
+	err = __register_cpu_notifier(&dummy_timer_cpu_nb);
 	if (err)
-		return err;
+		goto out;
 
 	/* We won't get a call on the boot CPU, so register immediately */
 	if (num_possible_cpus() > 1)
 		dummy_timer_setup();
 
-	return 0;
+out:
+	cpu_notifier_register_done();
+	return err;
 }
 early_initcall(dummy_timer_register);
diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
index 822ca03a87f7..d5eaedbe464f 100644
--- a/drivers/cpufreq/acpi-cpufreq.c
+++ b/drivers/cpufreq/acpi-cpufreq.c
@@ -906,15 +906,16 @@ static void __init acpi_cpufreq_boost_init(void)
 
 		acpi_cpufreq_driver.boost_supported = true;
 		acpi_cpufreq_driver.boost_enabled = boost_state(0);
-		get_online_cpus();
+
+		cpu_notifier_register_begin();
 
 		/* Force all MSRs to the same value */
 		boost_set_msrs(acpi_cpufreq_driver.boost_enabled,
 			       cpu_online_mask);
 
-		register_cpu_notifier(&boost_nb);
+		__register_cpu_notifier(&boost_nb);
 
-		put_online_cpus();
+		cpu_notifier_register_done();
 	}
 }
 
diff --git a/drivers/hwmon/coretemp.c b/drivers/hwmon/coretemp.c
index f31bc4c48644..6d02e3b06375 100644
--- a/drivers/hwmon/coretemp.c
+++ b/drivers/hwmon/coretemp.c
@@ -810,20 +810,20 @@ static int __init coretemp_init(void)
 	if (err)
 		goto exit;
 
-	get_online_cpus();
+	cpu_notifier_register_begin();
 	for_each_online_cpu(i)
 		get_core_online(i);
 
 #ifndef CONFIG_HOTPLUG_CPU
 	if (list_empty(&pdev_list)) {
-		put_online_cpus();
+		cpu_notifier_register_done();
 		err = -ENODEV;
 		goto exit_driver_unreg;
 	}
 #endif
 
-	register_hotcpu_notifier(&coretemp_cpu_notifier);
-	put_online_cpus();
+	__register_hotcpu_notifier(&coretemp_cpu_notifier);
+	cpu_notifier_register_done();
 	return 0;
 
 #ifndef CONFIG_HOTPLUG_CPU
@@ -838,8 +838,8 @@ static void __exit coretemp_exit(void)
 {
 	struct pdev_entry *p, *n;
 
-	get_online_cpus();
-	unregister_hotcpu_notifier(&coretemp_cpu_notifier);
+	cpu_notifier_register_begin();
+	__unregister_hotcpu_notifier(&coretemp_cpu_notifier);
 	mutex_lock(&pdev_list_mutex);
 	list_for_each_entry_safe(p, n, &pdev_list, list) {
 		platform_device_unregister(p->pdev);
@@ -847,7 +847,7 @@ static void __exit coretemp_exit(void)
 		kfree(p);
 	}
 	mutex_unlock(&pdev_list_mutex);
-	put_online_cpus();
+	cpu_notifier_register_done();
 	platform_driver_unregister(&coretemp_driver);
 }
 
diff --git a/drivers/hwmon/via-cputemp.c b/drivers/hwmon/via-cputemp.c
index 38944e94f65f..8df43c51de2c 100644
--- a/drivers/hwmon/via-cputemp.c
+++ b/drivers/hwmon/via-cputemp.c
@@ -319,7 +319,7 @@ static int __init via_cputemp_init(void)
 	if (err)
 		goto exit;
 
-	get_online_cpus();
+	cpu_notifier_register_begin();
 	for_each_online_cpu(i) {
 		struct cpuinfo_x86 *c = &cpu_data(i);
 
@@ -339,14 +339,14 @@ static int __init via_cputemp_init(void)
 
 #ifndef CONFIG_HOTPLUG_CPU
 	if (list_empty(&pdev_list)) {
-		put_online_cpus();
+		cpu_notifier_register_done();
 		err = -ENODEV;
 		goto exit_driver_unreg;
 	}
 #endif
 
-	register_hotcpu_notifier(&via_cputemp_cpu_notifier);
-	put_online_cpus();
+	__register_hotcpu_notifier(&via_cputemp_cpu_notifier);
+	cpu_notifier_register_done();
 	return 0;
 
 #ifndef CONFIG_HOTPLUG_CPU
@@ -361,8 +361,8 @@ static void __exit via_cputemp_exit(void)
 {
 	struct pdev_entry *p, *n;
 
-	get_online_cpus();
-	unregister_hotcpu_notifier(&via_cputemp_cpu_notifier);
+	cpu_notifier_register_begin();
+	__unregister_hotcpu_notifier(&via_cputemp_cpu_notifier);
 	mutex_lock(&pdev_list_mutex);
 	list_for_each_entry_safe(p, n, &pdev_list, list) {
 		platform_device_unregister(p->pdev);
@@ -370,7 +370,7 @@ static void __exit via_cputemp_exit(void)
 		kfree(p);
 	}
 	mutex_unlock(&pdev_list_mutex);
-	put_online_cpus();
+	cpu_notifier_register_done();
 	platform_driver_unregister(&via_cputemp_driver);
 }
 
diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
index 8e1939f564f4..51493ed4643b 100644
--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -681,14 +681,19 @@ static int __init intel_idle_init(void)
 	if (intel_idle_cpuidle_devices == NULL)
 		return -ENOMEM;
 
+	cpu_notifier_register_begin();
+
 	for_each_online_cpu(i) {
 		retval = intel_idle_cpu_init(i);
 		if (retval) {
+			cpu_notifier_register_done();
 			cpuidle_unregister_driver(&intel_idle_driver);
 			return retval;
 		}
 	}
-	register_cpu_notifier(&cpu_hotplug_notifier);
+	__register_cpu_notifier(&cpu_hotplug_notifier);
+
+	cpu_notifier_register_done();
 
 	return 0;
 }
@@ -698,10 +703,13 @@ static void __exit intel_idle_exit(void)
 	intel_idle_cpuidle_devices_uninit();
 	cpuidle_unregister_driver(&intel_idle_driver);
 
+	cpu_notifier_register_begin();
 
 	if (lapic_timer_reliable_states != LAPIC_TIMER_ALWAYS_RELIABLE)
 		on_each_cpu(__setup_broadcast_timer, (void *)false, 1);
-	unregister_cpu_notifier(&cpu_hotplug_notifier);
+	__unregister_cpu_notifier(&cpu_hotplug_notifier);
+
+	cpu_notifier_register_done();
 
 	return;
 }
diff --git a/drivers/oprofile/nmi_timer_int.c b/drivers/oprofile/nmi_timer_int.c
index 76f1c9357f39..9559829fb234 100644
--- a/drivers/oprofile/nmi_timer_int.c
+++ b/drivers/oprofile/nmi_timer_int.c
@@ -108,8 +108,8 @@ static void nmi_timer_shutdown(void)
 	struct perf_event *event;
 	int cpu;
 
-	get_online_cpus();
-	unregister_cpu_notifier(&nmi_timer_cpu_nb);
+	cpu_notifier_register_begin();
+	__unregister_cpu_notifier(&nmi_timer_cpu_nb);
 	for_each_possible_cpu(cpu) {
 		event = per_cpu(nmi_timer_events, cpu);
 		if (!event)
@@ -119,7 +119,7 @@ static void nmi_timer_shutdown(void)
 		perf_event_release_kernel(event);
 	}
 
-	put_online_cpus();
+	cpu_notifier_register_done();
 }
 
 static int nmi_timer_setup(void)
@@ -132,20 +132,23 @@ static int nmi_timer_setup(void)
 	do_div(period, HZ);
 	nmi_timer_attr.sample_period = period;
 
-	get_online_cpus();
-	err = register_cpu_notifier(&nmi_timer_cpu_nb);
+	cpu_notifier_register_begin();
+	err = __register_cpu_notifier(&nmi_timer_cpu_nb);
 	if (err)
 		goto out;
+
 	/* can't attach events to offline cpus: */
 	for_each_online_cpu(cpu) {
 		err = nmi_timer_start_cpu(cpu);
-		if (err)
-			break;
+		if (err) {
+			cpu_notifier_register_done();
+			nmi_timer_shutdown();
+			return err;
+		}
 	}
-	if (err)
-		nmi_timer_shutdown();
+
 out:
-	put_online_cpus();
+	cpu_notifier_register_done();
 	return err;
 }
 
diff --git a/drivers/powercap/intel_rapl.c b/drivers/powercap/intel_rapl.c
index 61b51e17d932..d9a0770b6c73 100644
--- a/drivers/powercap/intel_rapl.c
+++ b/drivers/powercap/intel_rapl.c
@@ -1374,6 +1374,9 @@ static int __init rapl_init(void)
 
 		return -ENODEV;
 	}
+
+	cpu_notifier_register_begin();
+
 	/* prevent CPU hotplug during detection */
 	get_online_cpus();
 	ret = rapl_detect_topology();
@@ -1385,20 +1388,23 @@ static int __init rapl_init(void)
 		ret = -ENODEV;
 		goto done;
 	}
-	register_hotcpu_notifier(&rapl_cpu_notifier);
+	__register_hotcpu_notifier(&rapl_cpu_notifier);
 done:
 	put_online_cpus();
+	cpu_notifier_register_done();
 
 	return ret;
 }
 
 static void __exit rapl_exit(void)
 {
+	cpu_notifier_register_begin();
 	get_online_cpus();
-	unregister_hotcpu_notifier(&rapl_cpu_notifier);
+	__unregister_hotcpu_notifier(&rapl_cpu_notifier);
 	rapl_unregister_powercap();
 	rapl_cleanup_data();
 	put_online_cpus();
+	cpu_notifier_register_done();
 }
 
 module_init(rapl_init);
diff --git a/drivers/scsi/bnx2fc/bnx2fc_fcoe.c b/drivers/scsi/bnx2fc/bnx2fc_fcoe.c
index 6287f6a8b79d..1d41f4b9114f 100644
--- a/drivers/scsi/bnx2fc/bnx2fc_fcoe.c
+++ b/drivers/scsi/bnx2fc/bnx2fc_fcoe.c
@@ -2592,12 +2592,16 @@ static int __init bnx2fc_mod_init(void)
 		spin_lock_init(&p->fp_work_lock);
 	}
 
+	cpu_notifier_register_begin();
+
 	for_each_online_cpu(cpu) {
 		bnx2fc_percpu_thread_create(cpu);
 	}
 
 	/* Initialize per CPU interrupt thread */
-	register_hotcpu_notifier(&bnx2fc_cpu_notifier);
+	__register_hotcpu_notifier(&bnx2fc_cpu_notifier);
+
+	cpu_notifier_register_done();
 
 	cnic_register_driver(CNIC_ULP_FCOE, &bnx2fc_cnic_cb);
 
@@ -2662,13 +2666,17 @@ static void __exit bnx2fc_mod_exit(void)
 	if (l2_thread)
 		kthread_stop(l2_thread);
 
-	unregister_hotcpu_notifier(&bnx2fc_cpu_notifier);
+	cpu_notifier_register_begin();
 
 	/* Destroy per cpu threads */
 	for_each_online_cpu(cpu) {
 		bnx2fc_percpu_thread_destroy(cpu);
 	}
 
+	__unregister_hotcpu_notifier(&bnx2fc_cpu_notifier);
+
+	cpu_notifier_register_done();
+
 	destroy_workqueue(bnx2fc_wq);
 	/*
 	 * detach from scsi transport
diff --git a/drivers/scsi/bnx2i/bnx2i_init.c b/drivers/scsi/bnx2i/bnx2i_init.c
index 34c294b42c84..80c03b452d61 100644
--- a/drivers/scsi/bnx2i/bnx2i_init.c
+++ b/drivers/scsi/bnx2i/bnx2i_init.c
@@ -537,11 +537,15 @@ static int __init bnx2i_mod_init(void)
 		p->iothread = NULL;
 	}
 
+	cpu_notifier_register_begin();
+
 	for_each_online_cpu(cpu)
 		bnx2i_percpu_thread_create(cpu);
 
 	/* Initialize per CPU interrupt thread */
-	register_hotcpu_notifier(&bnx2i_cpu_notifier);
+	__register_hotcpu_notifier(&bnx2i_cpu_notifier);
+
+	cpu_notifier_register_done();
 
 	return 0;
 
@@ -581,11 +585,15 @@ static void __exit bnx2i_mod_exit(void)
 	}
 	mutex_unlock(&bnx2i_dev_lock);
 
-	unregister_hotcpu_notifier(&bnx2i_cpu_notifier);
+	cpu_notifier_register_begin();
 
 	for_each_online_cpu(cpu)
 		bnx2i_percpu_thread_destroy(cpu);
 
+	__unregister_hotcpu_notifier(&bnx2i_cpu_notifier);
+
+	cpu_notifier_register_done();
+
 	iscsi_unregister_transport(&bnx2i_iscsi_transport);
 	cnic_unregister_driver(CNIC_ULP_ISCSI);
 }
diff --git a/drivers/scsi/fcoe/fcoe.c b/drivers/scsi/fcoe/fcoe.c
index f3170008ae71..d5e105b173f0 100644
--- a/drivers/scsi/fcoe/fcoe.c
+++ b/drivers/scsi/fcoe/fcoe.c
@@ -2633,14 +2633,18 @@ static int __init fcoe_init(void)
 		skb_queue_head_init(&p->fcoe_rx_list);
 	}
 
+	cpu_notifier_register_begin();
+
 	for_each_online_cpu(cpu)
 		fcoe_percpu_thread_create(cpu);
 
 	/* Initialize per CPU interrupt thread */
-	rc = register_hotcpu_notifier(&fcoe_cpu_notifier);
+	rc = __register_hotcpu_notifier(&fcoe_cpu_notifier);
 	if (rc)
 		goto out_free;
 
+	cpu_notifier_register_done();
+
 	/* Setup link change notification */
 	fcoe_dev_setup();
 
@@ -2655,6 +2659,9 @@ out_free:
 	for_each_online_cpu(cpu) {
 		fcoe_percpu_thread_destroy(cpu);
 	}
+
+	cpu_notifier_register_done();
+
 	mutex_unlock(&fcoe_config_mutex);
 	destroy_workqueue(fcoe_wq);
 	return rc;
@@ -2687,11 +2694,15 @@ static void __exit fcoe_exit(void)
 	}
 	rtnl_unlock();
 
-	unregister_hotcpu_notifier(&fcoe_cpu_notifier);
+	cpu_notifier_register_begin();
 
 	for_each_online_cpu(cpu)
 		fcoe_percpu_thread_destroy(cpu);
 
+	__unregister_hotcpu_notifier(&fcoe_cpu_notifier);
+
+	cpu_notifier_register_done();
+
 	mutex_unlock(&fcoe_config_mutex);
 
 	/*
diff --git a/drivers/thermal/x86_pkg_temp_thermal.c b/drivers/thermal/x86_pkg_temp_thermal.c
index 081fd7e6a9f0..9ea3d9d49ffc 100644
--- a/drivers/thermal/x86_pkg_temp_thermal.c
+++ b/drivers/thermal/x86_pkg_temp_thermal.c
@@ -590,12 +590,12 @@ static int __init pkg_temp_thermal_init(void)
 	platform_thermal_package_rate_control =
 			pkg_temp_thermal_platform_thermal_rate_control;
 
-	get_online_cpus();
+	cpu_notifier_register_begin();
 	for_each_online_cpu(i)
 		if (get_core_online(i))
 			goto err_ret;
-	register_hotcpu_notifier(&pkg_temp_thermal_notifier);
-	put_online_cpus();
+	__register_hotcpu_notifier(&pkg_temp_thermal_notifier);
+	cpu_notifier_register_done();
 
 	pkg_temp_debugfs_init(); /* Don't care if fails */
 
@@ -604,7 +604,7 @@ static int __init pkg_temp_thermal_init(void)
 err_ret:
 	for_each_online_cpu(i)
 		put_core_offline(i);
-	put_online_cpus();
+	cpu_notifier_register_done();
 	kfree(pkg_work_scheduled);
 	platform_thermal_package_notify = NULL;
 	platform_thermal_package_rate_control = NULL;
@@ -617,8 +617,8 @@ static void __exit pkg_temp_thermal_exit(void)
 	struct phy_dev_entry *phdev, *n;
 	int i;
 
-	get_online_cpus();
-	unregister_hotcpu_notifier(&pkg_temp_thermal_notifier);
+	cpu_notifier_register_begin();
+	__unregister_hotcpu_notifier(&pkg_temp_thermal_notifier);
 	mutex_lock(&phy_dev_list_mutex);
 	list_for_each_entry_safe(phdev, n, &phy_dev_list, list) {
 		/* Retore old MSR value for package thermal interrupt */
@@ -636,7 +636,7 @@ static void __exit pkg_temp_thermal_exit(void)
 	for_each_online_cpu(i)
 		cancel_delayed_work_sync(
 			&per_cpu(pkg_temp_thermal_threshold_work, i));
-	put_online_cpus();
+	cpu_notifier_register_done();
 
 	kfree(pkg_work_scheduled);
 
diff --git a/drivers/watchdog/octeon-wdt-main.c b/drivers/watchdog/octeon-wdt-main.c
index 461208831428..4baf2d788920 100644
--- a/drivers/watchdog/octeon-wdt-main.c
+++ b/drivers/watchdog/octeon-wdt-main.c
@@ -708,10 +708,13 @@ static int __init octeon_wdt_init(void)
 
 	cpumask_clear(&irq_enabled_cpus);
 
+	cpu_notifier_register_begin();
 	for_each_online_cpu(cpu)
 		octeon_wdt_setup_interrupt(cpu);
 
-	register_hotcpu_notifier(&octeon_wdt_cpu_notifier);
+	__register_hotcpu_notifier(&octeon_wdt_cpu_notifier);
+	cpu_notifier_register_done();
+
 out:
 	return ret;
 }
@@ -725,7 +728,8 @@ static void __exit octeon_wdt_cleanup(void)
 
 	misc_deregister(&octeon_wdt_miscdev);
 
-	unregister_hotcpu_notifier(&octeon_wdt_cpu_notifier);
+	cpu_notifier_register_begin();
+	__unregister_hotcpu_notifier(&octeon_wdt_cpu_notifier);
 
 	for_each_online_cpu(cpu) {
 		int core = cpu2core(cpu);
@@ -734,6 +738,9 @@ static void __exit octeon_wdt_cleanup(void)
 		/* Free the interrupt handler */
 		free_irq(OCTEON_IRQ_WDOG0 + core, octeon_wdt_poke_irq);
 	}
+
+	cpu_notifier_register_done();
+
 	/*
 	 * Disable the boot-bus memory, the code it points to is soon
 	 * to go missing.
diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 61a6ac8fa8fc..b7a506f2bb14 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -604,19 +604,29 @@ static void __init balloon_add_region(unsigned long start_pfn,
 	}
 }
 
+static int alloc_balloon_scratch_page(int cpu)
+{
+	if (per_cpu(balloon_scratch_page, cpu) != NULL)
+		return 0;
+
+	per_cpu(balloon_scratch_page, cpu) = alloc_page(GFP_KERNEL);
+	if (per_cpu(balloon_scratch_page, cpu) == NULL) {
+		pr_warn("Failed to allocate balloon_scratch_page for cpu %d\n", cpu);
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+
+
 static int balloon_cpu_notify(struct notifier_block *self,
 				    unsigned long action, void *hcpu)
 {
 	int cpu = (long)hcpu;
 	switch (action) {
 	case CPU_UP_PREPARE:
-		if (per_cpu(balloon_scratch_page, cpu) != NULL)
-			break;
-		per_cpu(balloon_scratch_page, cpu) = alloc_page(GFP_KERNEL);
-		if (per_cpu(balloon_scratch_page, cpu) == NULL) {
-			pr_warn("Failed to allocate balloon_scratch_page for cpu %d\n", cpu);
+		if (alloc_balloon_scratch_page(cpu))
 			return NOTIFY_BAD;
-		}
 		break;
 	default:
 		break;
@@ -636,15 +646,17 @@ static int __init balloon_init(void)
 		return -ENODEV;
 
 	if (!xen_feature(XENFEAT_auto_translated_physmap)) {
-		for_each_online_cpu(cpu)
-		{
-			per_cpu(balloon_scratch_page, cpu) = alloc_page(GFP_KERNEL);
-			if (per_cpu(balloon_scratch_page, cpu) == NULL) {
-				pr_warn("Failed to allocate balloon_scratch_page for cpu %d\n", cpu);
+		register_cpu_notifier(&balloon_cpu_notifier);
+
+		get_online_cpus();
+		for_each_online_cpu(cpu) {
+			if (alloc_balloon_scratch_page(cpu)) {
+				put_online_cpus();
+				unregister_cpu_notifier(&balloon_cpu_notifier);
 				return -ENOMEM;
 			}
 		}
-		register_cpu_notifier(&balloon_cpu_notifier);
+		put_online_cpus();
 	}
 
 	pr_info("Initialising balloon driver\n");