[PATCH v2 4/6] ACPI, PCI: add acpi_pci_roots protection

[Taku Izumi <izumi.taku@jp.fujitsu.com>]

Use mutex and RCU to protect global acpi_pci_roots list against
PCI host bridge hotplug operations.

RCU is used to avoid possible deadlock in function acpi_pci_find_root()
and acpi_get_pci_rootbridge_handle(). A possible call graph:
acpi_pci_register_driver()
	mutex_lock(&acpi_pci_root_lock)
		driver->add(root)
			......
				acpi_pci_find_root()

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Taku Izumi <izumi.taku@jp.fujitsu.com>
---
 drivers/acpi/pci_root.c |   50 +++++++++++++++++++++++++++++++-----------------
 1 file changed, 33 insertions(+), 17 deletions(-)

Index: Bjorn-next-0903/drivers/acpi/pci_root.c
===================================================================
--- Bjorn-next-0903.orig/drivers/acpi/pci_root.c
+++ Bjorn-next-0903/drivers/acpi/pci_root.c
@@ -28,6 +28,7 @@
 #include <linux/init.h>
 #include <linux/types.h>
 #include <linux/mutex.h>
+#include <linux/rculist.h>
 #include <linux/pm.h>
 #include <linux/pm_runtime.h>
 #include <linux/pci.h>
@@ -86,7 +87,7 @@ int acpi_pci_register_driver(struct acpi
 	mutex_lock(&acpi_pci_root_lock);
 	list_add_tail(&driver->node, &acpi_pci_drivers);
 	if (driver->add)
-		list_for_each_entry(root, &acpi_pci_roots, node) {
+		list_for_each_entry_rcu(root, &acpi_pci_roots, node) {
 			driver->add(root->device->handle);
 			n++;
 		}
@@ -103,7 +104,7 @@ void acpi_pci_unregister_driver(struct a
 	mutex_lock(&acpi_pci_root_lock);
 	list_del(&driver->node);
 	if (driver->remove)
-		list_for_each_entry(root, &acpi_pci_roots, node)
+		list_for_each_entry_rcu(root, &acpi_pci_roots, node)
 			driver->remove(root->device->handle);
 	mutex_unlock(&acpi_pci_root_lock);
 }
@@ -112,14 +113,19 @@ EXPORT_SYMBOL(acpi_pci_unregister_driver
 acpi_handle acpi_get_pci_rootbridge_handle(unsigned int seg, unsigned int bus)
 {
 	struct acpi_pci_root *root;
+	struct acpi_handle *handle = NULL;
 	
-	list_for_each_entry(root, &acpi_pci_roots, node)
+	rcu_read_lock();
+	list_for_each_entry_rcu(root, &acpi_pci_roots, node)
 		if ((root->segment == (u16) seg) &&
-		    (root->secondary.start == (u16) bus))
-			return root->device->handle;
-	return NULL;		
-}
+		    (root->secondary.start == (u16) bus)) {
+			handle = root->device->handle;
+			break;
+		}
+	rcu_read_unlock();
 
+	return handle;
+}
 EXPORT_SYMBOL_GPL(acpi_get_pci_rootbridge_handle);
 
 /**
@@ -266,10 +272,14 @@ struct acpi_pci_root *acpi_pci_find_root
 {
 	struct acpi_pci_root *root;
 
-	list_for_each_entry(root, &acpi_pci_roots, node) {
-		if (root->device->handle == handle)
+	rcu_read_lock();
+	list_for_each_entry_rcu(root, &acpi_pci_roots, node)
+		if (root->device->handle == handle) {
+			rcu_read_unlock();
 			return root;
-	}
+		}
+	rcu_read_unlock();
+
 	return NULL;
 }
 EXPORT_SYMBOL_GPL(acpi_pci_find_root);
@@ -506,8 +516,9 @@ static int __devinit acpi_pci_root_add(s
 	 * TBD: Need PCI interface for enumeration/configuration of roots.
 	 */
 
-	/* TBD: Locking */
-	list_add_tail(&root->node, &acpi_pci_roots);
+	mutex_lock(&acpi_pci_root_lock);
+	list_add_tail_rcu(&root->node, &acpi_pci_roots);
+	mutex_unlock(&acpi_pci_root_lock);
 
 	printk(KERN_INFO PREFIX "%s [%s] (domain %04x %pR)\n",
 	       acpi_device_name(device), acpi_device_bid(device),
@@ -526,7 +537,7 @@ static int __devinit acpi_pci_root_add(s
 			    "Bus %04x:%02x not present in PCI namespace\n",
 			    root->segment, (unsigned int)root->secondary.start);
 		result = -ENODEV;
-		goto end;
+		goto out_del_root;
 	}
 
 	/*
@@ -536,7 +547,7 @@ static int __devinit acpi_pci_root_add(s
 	 */
 	result = acpi_pci_bind_root(device);
 	if (result)
-		goto end;
+		goto out_del_root;
 
 	/*
 	 * PCI Routing Table
@@ -614,9 +625,12 @@ static int __devinit acpi_pci_root_add(s
 
 	return 0;
 
+out_del_root:
+	mutex_lock(&acpi_pci_root_lock);
+	list_del_rcu(&root->node);
+	mutex_unlock(&acpi_pci_root_lock);
+	synchronize_rcu();
 end:
-	if (!list_empty(&root->node))
-		list_del(&root->node);
 	kfree(root);
 	return result;
 }
@@ -646,11 +660,13 @@ static int acpi_pci_root_remove(struct a
 	list_for_each_entry(driver, &acpi_pci_drivers, node)
 		if (driver->remove)
 			driver->remove(root->device->handle);
-	mutex_unlock(&acpi_pci_root_lock);
 
 	device_set_run_wake(root->bus->bridge, false);
 	pci_acpi_remove_bus_pm_notifier(device);
 
+	list_del_rcu(&root->node);
+	mutex_unlock(&acpi_pci_root_lock);
+	synchronize_rcu();
 	kfree(root);
 	return 0;
 }