ACPICA: Fix namespace race condition

Fixes a race condition between method execution and namespace
walks that can possibly fault. Problem was apparently introduced
in version 20100528 as a result of a performance optimization
that reduces the number of namespace walks upon method exit
by using the delete_namespace_subtree function instead of the
delete_namespace_by_owner function used previously. Bug is in
the delete_namespace_subtree function.

Signed-off-by: Dana Myers <dana.myers@oracle.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Reviewed-by: Rafael Wysocki <rjw@sisk.pl>
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/acpi/acpica/nsalloc.c

@@ -341,6 +341,7 @@ void acpi_ns_delete_namespace_subtree(struct acpi_namespace_node *parent_node)
 {
 	struct acpi_namespace_node *child_node = NULL;
 	u32 level = 1;
+	acpi_status status;
 
 	ACPI_FUNCTION_TRACE(ns_delete_namespace_subtree);
 
@@ -348,6 +349,13 @@ void acpi_ns_delete_namespace_subtree(struct acpi_namespace_node *parent_node)
 		return_VOID;
 	}
 
+	/* Lock namespace for possible update */
+
+	status = acpi_ut_acquire_mutex(ACPI_MTX_NAMESPACE);
+	if (ACPI_FAILURE(status)) {
+		return_VOID;
+	}
+
 	/*
 	 * Traverse the tree of objects until we bubble back up
 	 * to where we started.
@@ -397,6 +405,7 @@ void acpi_ns_delete_namespace_subtree(struct acpi_namespace_node *parent_node)
 		}
 	}
 
+	(void)acpi_ut_release_mutex(ACPI_MTX_NAMESPACE);
 	return_VOID;
 }