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, 7 insertions, 6 deletions

diff --git a/drivers/acpi/acpica/exconfig.c b/drivers/acpi/acpica/exconfig.c
index 70b39c7daeab..3deb20a126b2 100644
--- a/drivers/acpi/acpica/exconfig.c
+++ b/drivers/acpi/acpica/exconfig.c
@@ -520,13 +520,14 @@ acpi_status acpi_ex_unload_table(union acpi_operand_object *ddb_handle)
                 }
         }
 
-        /*
-         * Delete the entire namespace under this table Node
-         * (Offset contains the table_id)
-         */
-        acpi_tb_delete_namespace_by_owner(table_index);
-        (void)acpi_tb_release_owner_id(table_index);
+        /* Delete the portion of the namespace owned by this table */
+
+        status = acpi_tb_delete_namespace_by_owner(table_index);
+        if (ACPI_FAILURE(status)) {
+                return_ACPI_STATUS(status);
+        }
 
+        (void)acpi_tb_release_owner_id(table_index);
         acpi_tb_set_table_loaded_flag(table_index, FALSE);
 
         /* Table unloaded, remove a reference to the ddb_handle object */