feat(task): deny an interrupt context in Kernel::exit_task

Author: yvt

src/constance/src/kernel/error.rs

@@ -200,7 +200,7 @@ define_error! {
     ///
     /// [`Kernel::exit_task`]: super::Kernel::exit_task
     pub enum ExitTaskError: BadContextError {
-        /// CPU Lock is active.
+        /// CPU Lock is active, or the current context is not a task context.
         BadContext,
     }
 }

src/constance/src/kernel/task.rs

@@ -344,7 +344,9 @@ impl Init for TaskSt {
 
 /// Implements [`Kernel::exit_task`].
 pub(super) unsafe fn exit_current_task<System: Kernel>() -> Result<!, ExitTaskError> {
-    // TODO: Deny interrupt context
+    if System::is_interrupt_context() {
+        return Err(ExitTaskError::BadContext);
+    }
 
     // If CPU Lock is inactive, activate it.
     // TODO: If `is_cpu_lock_active() == true`, assert that it was an

src/constance_test_suite/src/kernel_tests/interrupt_disallowed_services.rs

@@ -59,6 +59,13 @@ fn isr<System: Kernel, D: Driver<App<System>>>(_: usize) {
         System::boost_priority(),
         Err(kernel::BoostPriorityError::BadContext),
     );
+    assert_eq!(
+        unsafe { System::exit_task() },
+        Err(kernel::ExitTaskError::BadContext),
+    );
+
+    // Blocking system services
+    assert_eq!(System::park(), Err(kernel::ParkError::BadContext));
 
     D::success();
 }