net/iucv/iucv.c: Fix CPU hotplug callback registration

Subsystems that want to register CPU hotplug callbacks, as well as perform
initialization for the CPUs that are already online, often do it as shown
below:

	get_online_cpus();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	register_cpu_notifier(&foobar_cpu_notifier);

	put_online_cpus();

This is wrong, since it is prone to ABBA deadlocks involving the
cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
with CPU hotplug operations).

Instead, the correct and race-free way of performing the callback
registration is:

	cpu_notifier_register_begin();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	/* Note the use of the double underscored version of the API */
	__register_cpu_notifier(&foobar_cpu_notifier);

	cpu_notifier_register_done();

Fix the code in net/iucv/iucv.c by using this latter form of callback
registration. Also, provide helper functions to perform the common memory
allocations and frees, to condense repetitive code.

Cc: Ursula Braun <ursula.braun@de.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Acked-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

net/iucv/iucv.c

@@ -621,47 +621,59 @@ static void iucv_disable(void)
 	put_online_cpus();
 }
 
-static int iucv_cpu_notify(struct notifier_block *self,
-				     unsigned long action, void *hcpu)
+static void free_iucv_data(int cpu)
 {
-	cpumask_t cpumask;
-	long cpu = (long) hcpu;
+	kfree(iucv_param_irq[cpu]);
+	iucv_param_irq[cpu] = NULL;
+	kfree(iucv_param[cpu]);
+	iucv_param[cpu] = NULL;
+	kfree(iucv_irq_data[cpu]);
+	iucv_irq_data[cpu] = NULL;
+}
 
-	switch (action) {
-	case CPU_UP_PREPARE:
-	case CPU_UP_PREPARE_FROZEN:
+static int alloc_iucv_data(int cpu)
+{
+	/* Note: GFP_DMA used to get memory below 2G */
 	iucv_irq_data[cpu] = kmalloc_node(sizeof(struct iucv_irq_data),
 			     GFP_KERNEL|GFP_DMA, cpu_to_node(cpu));
 	if (!iucv_irq_data[cpu])
-			return notifier_from_errno(-ENOMEM);
+		goto out_free;
 
+	/* Allocate parameter blocks. */
 	iucv_param[cpu] = kmalloc_node(sizeof(union iucv_param),
 			  GFP_KERNEL|GFP_DMA, cpu_to_node(cpu));
-		if (!iucv_param[cpu]) {
-			kfree(iucv_irq_data[cpu]);
-			iucv_irq_data[cpu] = NULL;
-			return notifier_from_errno(-ENOMEM);
-		}
+	if (!iucv_param[cpu])
+		goto out_free;
+
 	iucv_param_irq[cpu] = kmalloc_node(sizeof(union iucv_param),
 			  GFP_KERNEL|GFP_DMA, cpu_to_node(cpu));
-		if (!iucv_param_irq[cpu]) {
-			kfree(iucv_param[cpu]);
-			iucv_param[cpu] = NULL;
-			kfree(iucv_irq_data[cpu]);
-			iucv_irq_data[cpu] = NULL;
+	if (!iucv_param_irq[cpu])
+		goto out_free;
+
+	return 0;
+
+out_free:
+	free_iucv_data(cpu);
+	return -ENOMEM;
+}
+
+static int iucv_cpu_notify(struct notifier_block *self,
+				     unsigned long action, void *hcpu)
+{
+	cpumask_t cpumask;
+	long cpu = (long) hcpu;
+
+	switch (action) {
+	case CPU_UP_PREPARE:
+	case CPU_UP_PREPARE_FROZEN:
+		if (alloc_iucv_data(cpu))
 			return notifier_from_errno(-ENOMEM);
-		}
 		break;
 	case CPU_UP_CANCELED:
 	case CPU_UP_CANCELED_FROZEN:
 	case CPU_DEAD:
 	case CPU_DEAD_FROZEN:
-		kfree(iucv_param_irq[cpu]);
-		iucv_param_irq[cpu] = NULL;
-		kfree(iucv_param[cpu]);
-		iucv_param[cpu] = NULL;
-		kfree(iucv_irq_data[cpu]);
-		iucv_irq_data[cpu] = NULL;
+		free_iucv_data(cpu);
 		break;
 	case CPU_ONLINE:
 	case CPU_ONLINE_FROZEN:
@@ -2025,33 +2037,20 @@ static int __init iucv_init(void)
 		goto out_int;
 	}
 
-	for_each_online_cpu(cpu) {
-		/* Note: GFP_DMA used to get memory below 2G */
-		iucv_irq_data[cpu] = kmalloc_node(sizeof(struct iucv_irq_data),
-				     GFP_KERNEL|GFP_DMA, cpu_to_node(cpu));
-		if (!iucv_irq_data[cpu]) {
-			rc = -ENOMEM;
-			goto out_free;
-		}
+	cpu_notifier_register_begin();
 
-		/* Allocate parameter blocks. */
-		iucv_param[cpu] = kmalloc_node(sizeof(union iucv_param),
-				  GFP_KERNEL|GFP_DMA, cpu_to_node(cpu));
-		if (!iucv_param[cpu]) {
-			rc = -ENOMEM;
-			goto out_free;
-		}
-		iucv_param_irq[cpu] = kmalloc_node(sizeof(union iucv_param),
-				  GFP_KERNEL|GFP_DMA, cpu_to_node(cpu));
-		if (!iucv_param_irq[cpu]) {
+	for_each_online_cpu(cpu) {
+		if (alloc_iucv_data(cpu)) {
 			rc = -ENOMEM;
 			goto out_free;
 		}
-
 	}
-	rc = register_hotcpu_notifier(&iucv_cpu_notifier);
+	rc = __register_hotcpu_notifier(&iucv_cpu_notifier);
 	if (rc)
 		goto out_free;
+
+	cpu_notifier_register_done();
+
 	rc = register_reboot_notifier(&iucv_reboot_notifier);
 	if (rc)
 		goto out_cpu;
@@ -2069,16 +2068,14 @@ static int __init iucv_init(void)
 out_reboot:
 	unregister_reboot_notifier(&iucv_reboot_notifier);
 out_cpu:
-	unregister_hotcpu_notifier(&iucv_cpu_notifier);
+	cpu_notifier_register_begin();
+	__unregister_hotcpu_notifier(&iucv_cpu_notifier);
 out_free:
-	for_each_possible_cpu(cpu) {
-		kfree(iucv_param_irq[cpu]);
-		iucv_param_irq[cpu] = NULL;
-		kfree(iucv_param[cpu]);
-		iucv_param[cpu] = NULL;
-		kfree(iucv_irq_data[cpu]);
-		iucv_irq_data[cpu] = NULL;
-	}
+	for_each_possible_cpu(cpu)
+		free_iucv_data(cpu);
+
+	cpu_notifier_register_done();
+
 	root_device_unregister(iucv_root);
 out_int:
 	unregister_external_interrupt(0x4000, iucv_external_interrupt);
@@ -2105,15 +2102,11 @@ static void __exit iucv_exit(void)
 		kfree(p);
 	spin_unlock_irq(&iucv_queue_lock);
 	unregister_reboot_notifier(&iucv_reboot_notifier);
-	unregister_hotcpu_notifier(&iucv_cpu_notifier);
-	for_each_possible_cpu(cpu) {
-		kfree(iucv_param_irq[cpu]);
-		iucv_param_irq[cpu] = NULL;
-		kfree(iucv_param[cpu]);
-		iucv_param[cpu] = NULL;
-		kfree(iucv_irq_data[cpu]);
-		iucv_irq_data[cpu] = NULL;
-	}
+	cpu_notifier_register_begin();
+	__unregister_hotcpu_notifier(&iucv_cpu_notifier);
+	for_each_possible_cpu(cpu)
+		free_iucv_data(cpu);
+	cpu_notifier_register_done();
 	root_device_unregister(iucv_root);
 	bus_unregister(&iucv_bus);
 	unregister_external_interrupt(0x4000, iucv_external_interrupt);