x86, irq, ACPI: Introduce a mutex to protect IOAPIC operations from hotplug

We are going to support ACPI based IOAPIC hotplug, so introduce a mutex
to protect IOAPIC data structures from IOAPIC hotplug. We choose to
serialize in ACPI instead of in the IOAPIC core because:

1) currently we only plan to support ACPI based IOAPIC hotplug
2) it's much more cleaner and easier
3) It does't affect IOAPIC discovered by devicetree, SFI and mpparse.

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Len Brown <len.brown@intel.com>
Cc: Pavel Machek <pavel@ucw.cz>
Link: http://lkml.kernel.org/r/1414908273-7552-15-git-send-email-jiang.liu@linux.intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/acpi/boot.c

@@ -76,6 +76,19 @@ int acpi_fix_pin2_polarity __initdata;
 static u64 acpi_lapic_addr __initdata = APIC_DEFAULT_PHYS_BASE;
 #endif
 
+/*
+ * Locks related to IOAPIC hotplug
+ * Hotplug side:
+ *	->device_hotplug_lock
+ *		->acpi_ioapic_lock
+ *			->ioapic_lock
+ * Interrupt mapping side:
+ *	->acpi_ioapic_lock
+ *		->ioapic_mutex
+ *			->ioapic_lock
+ */
+static DEFINE_MUTEX(acpi_ioapic_lock);
+
 /* --------------------------------------------------------------------------
                               Boot-time Configuration
    -------------------------------------------------------------------------- */
@@ -609,8 +622,10 @@ int acpi_gsi_to_irq(u32 gsi, unsigned int *irqp)
 	if (acpi_irq_model == ACPI_IRQ_MODEL_PIC) {
 		*irqp = gsi;
 	} else {
+		mutex_lock(&acpi_ioapic_lock);
 		irq = mp_map_gsi_to_irq(gsi,
 					IOAPIC_MAP_ALLOC | IOAPIC_MAP_CHECK);
+		mutex_unlock(&acpi_ioapic_lock);
 		if (irq < 0)
 			return -1;
 		*irqp = irq;
@@ -650,7 +665,9 @@ static int acpi_register_gsi_ioapic(struct device *dev, u32 gsi,
 	int irq = gsi;
 
 #ifdef CONFIG_X86_IO_APIC
+	mutex_lock(&acpi_ioapic_lock);
 	irq = mp_register_gsi(dev, gsi, trigger, polarity);
+	mutex_unlock(&acpi_ioapic_lock);
 #endif
 
 	return irq;
@@ -659,7 +676,9 @@ static int acpi_register_gsi_ioapic(struct device *dev, u32 gsi,
 static void acpi_unregister_gsi_ioapic(u32 gsi)
 {
 #ifdef CONFIG_X86_IO_APIC
+	mutex_lock(&acpi_ioapic_lock);
 	mp_unregister_gsi(gsi);
+	mutex_unlock(&acpi_ioapic_lock);
 #endif
 }
 
@@ -1187,7 +1206,9 @@ static void __init acpi_process_madt(void)
 			/*
 			 * Parse MADT IO-APIC entries
 			 */
+			mutex_lock(&acpi_ioapic_lock);
 			error = acpi_parse_madt_ioapic_entries();
+			mutex_unlock(&acpi_ioapic_lock);
 			if (!error) {
 				acpi_set_irq_model_ioapic();