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>

1 files changed, 15 insertions, 0 deletions

diff --git a/drivers/acpi/acpica/acutils.h b/drivers/acpi/acpica/acutils.h
index 80d8813484fe..897810ba0ccc 100644
--- a/drivers/acpi/acpica/acutils.h
+++ b/drivers/acpi/acpica/acutils.h
@@ -346,6 +346,21 @@ acpi_status
 acpi_ut_execute_sxds(struct acpi_namespace_node *device_node, u8 * highest);
 
 /*
+ * utlock - reader/writer locks
+ */
+acpi_status acpi_ut_create_rw_lock(struct acpi_rw_lock *lock);
+
+void acpi_ut_delete_rw_lock(struct acpi_rw_lock *lock);
+
+acpi_status acpi_ut_acquire_read_lock(struct acpi_rw_lock *lock);
+
+acpi_status acpi_ut_release_read_lock(struct acpi_rw_lock *lock);
+
+acpi_status acpi_ut_acquire_write_lock(struct acpi_rw_lock *lock);
+
+void acpi_ut_release_write_lock(struct acpi_rw_lock *lock);
+
+/*
  * utobject - internal object create/delete/cache routines
  */
 union acpi_operand_object *acpi_ut_create_internal_object_dbg(const char