ACPICA: Fix AcpiWalkNamespace race condition with table unload

Added a reader/writer locking mechanism to allow multiple
concurrent namespace walks (readers), but a dynamic table unload
will have exclusive access to the namespace. This fixes a problem
where a table unload could delete the portion of the namespace that
is currently being examined by a walk.  Adds a new file, utlock.c
that implements the reader/writer lock mechanism. ACPICA BZ 749.

http://www.acpica.org/bugzilla/show_bug.cgi?id=749

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
diff --git a/drivers/acpi/acpica/aclocal.h b/drivers/acpi/acpica/aclocal.h
index 6feebc8..18a8d96 100644
--- a/drivers/acpi/acpica/aclocal.h
+++ b/drivers/acpi/acpica/aclocal.h
@@ -108,6 +108,14 @@
 #endif
 #endif
 
+/* Lock structure for reader/writer interfaces */
+
+struct acpi_rw_lock {
+	acpi_mutex writer_mutex;
+	acpi_mutex reader_mutex;
+	u32 num_readers;
+};
+
 /*
  * Predefined handles for spinlocks used within the subsystem.
  * These spinlocks are created by acpi_ut_mutex_initialize