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, 14 insertions, 2 deletions

diff --git a/drivers/acpi/acpica/dsinit.c b/drivers/acpi/acpica/dsinit.c
index eb144b13d8fa..3aae13f30c5e 100644
--- a/drivers/acpi/acpica/dsinit.c
+++ b/drivers/acpi/acpica/dsinit.c
@@ -180,11 +180,23 @@ acpi_ds_initialize_objects(u32 table_index,
 
         /* Walk entire namespace from the supplied root */
 
-        status = acpi_walk_namespace(ACPI_TYPE_ANY, start_node, ACPI_UINT32_MAX,
-                                     acpi_ds_init_one_object, &info, NULL);
+        status = acpi_ut_acquire_mutex(ACPI_MTX_NAMESPACE);
+        if (ACPI_FAILURE(status)) {
+                return_ACPI_STATUS(status);
+        }
+
+        /*
+         * We don't use acpi_walk_namespace since we do not want to acquire
+         * the namespace reader lock.
+         */
+        status =
+            acpi_ns_walk_namespace(ACPI_TYPE_ANY, start_node, ACPI_UINT32_MAX,
+                                   ACPI_NS_WALK_UNLOCK, acpi_ds_init_one_object,
+                                   &info, NULL);
         if (ACPI_FAILURE(status)) {
                 ACPI_EXCEPTION((AE_INFO, status, "During WalkNamespace"));
         }
+        (void)acpi_ut_release_mutex(ACPI_MTX_NAMESPACE);
 
         status = acpi_get_table_by_index(table_index, &table);
         if (ACPI_FAILURE(status)) {