sys/program_stop: add hack to workaround Bluetooth lockup

Many Bluetooth tasks can get stuck (can't be canceled) if the Bluetooth
chip crashes. Adding checks for this at every yield point would be
very expensive in terms of code size. So for now, we just add another
hack to cancel all tasks on shutdown to avoid undefined behavior.

In some cases, this undefined behavior was causing the hub to not power
off unless the batteries were removed.

Issue: pybricks/support#1095

CHANGELOG.md

@@ -4,6 +4,12 @@
 
 ## [Unreleased]
 
+### Fixed
+- Fixed hub will not power off when Bluetooth chip crashes on City and Technic hubs ([support#1095]).
+
+[support#1095]: https://github.com/pybricks/support/issues/1095
+
+
 ## [3.3.0b6] - 2023-06-02
 
 ### Added

lib/pbio/sys/program_stop.c

@@ -8,6 +8,7 @@
 #include <stdbool.h>
 #include <stddef.h>
 
+#include <pbdrv/bluetooth.h>
 #include <pbio/button.h>
 #include <pbio/main.h>
 
@@ -31,6 +32,12 @@ static bool stop_button_pressed;
  */
 void pbsys_program_stop(bool force_stop) {
     if (pbsys_status_test(PBIO_PYBRICKS_STATUS_USER_PROGRAM_RUNNING)) {
+        if (force_stop) {
+            // HACK: Bluetooth drivers have issues with pending tasks not being
+            // cancellable, so this should force them to be canceled and avoid
+            // undefined behavior due to use after free.
+            pbdrv_bluetooth_power_on(false);
+        }
         pbsys_main_stop_program(force_stop);
     }
 }

pybricks/util_pb/pb_task.c

@@ -49,6 +49,7 @@ void pb_wait_task(pbio_task_t *task, mp_int_t timeout) {
                // requested. See https://github.com/pybricks/pybricks-micropython/pull/129
                // We can remove this hack once we can ensure that task
                // cancellation does not fail (for known cases).
+               // Also see hack in pbsys_program_stop().
                && !pbsys_status_test(PBIO_PYBRICKS_STATUS_SHUTDOWN_REQUEST)
                #endif
                ) {