Task initally exec'ing with success. Some errors need to be investigated.

- Directory creation, file read/write is OK.
- Cannot reuse old task's fds. They are not recycled for some reason.
- Problems with fork/clone/exit. They fail for a reason.

src/api/space.c

@@ -59,16 +59,6 @@ int sys_unmap(syscall_context_t *regs)
 	else if (!(target = find_task(tid)))
 		return -ESRCH;
 
-	/*
-	 * These special values mean unmap all the mappings
-	 * from task space except the kernel mappings
-	 */
-	if (virtual == UNMAP_ALL_SPACE &&
-	    npages == UNMAP_ALL_SPACE) {
-		remove_mapping_pgd_all_user(target->pgd);
-		return 0;
-	}
-
 	for (int i = 0; i < npages; i++) {
 		ret = remove_mapping_pgd(virtual + i * PAGE_SIZE, target->pgd);
 		if (ret)

src/api/syscall.c

@@ -87,7 +87,7 @@ void do_exchange_registers(struct ktcb *task, struct exregs_data *exregs)
  * the register context of a thread. The thread's registers can be
  * set only when the thread is in user mode. A newly created thread
  * that is the copy of another thread (forked or cloned) will also
- * be given its user mode context on the first chance to execute so 
+ * be given its user mode context on the first chance to execute so
  * such threads can also be modified by this call before execution.
  *
  * A thread executing in the kernel cannot be modified since this
@@ -119,6 +119,9 @@ int sys_exchange_registers(syscall_context_t *regs)
 		goto out;
 	}
 
+#if 0
+	A suspended thread implies it cannot do any harm
+	even if it is in kernel mode.
 	/*
 	 * The thread must be in user mode for its context
 	 * to be modified.
@@ -127,6 +130,7 @@ int sys_exchange_registers(syscall_context_t *regs)
 		err = -EPERM;
 		goto out;
 	}
+#endif
 
 	/* Copy registers */
 	do_exchange_registers(task, exregs);

src/api/thread.c

@@ -49,6 +49,47 @@ int thread_suspend(struct task_ids *ids)
 	return ret;
 }
 
+int arch_clear_thread(struct ktcb *task)
+{
+	memset(&task->context, 0, sizeof(task->context));
+	task->context.spsr = ARM_MODE_USR;
+
+	/* Clear the page tables */
+	remove_mapping_pgd_all_user(task->pgd);
+
+	return 0;
+}
+
+int thread_recycle(struct task_ids *ids)
+{
+	struct ktcb *task;
+	int ret;
+
+	if (!(task = find_task(ids->tid)))
+		return -ESRCH;
+
+	if ((ret = thread_suspend(ids)) < 0)
+		return ret;
+
+	/*
+	 * If there are any sleepers on any of the task's
+	 * waitqueues, we need to wake those tasks up.
+	 */
+	wake_up_all(&task->wqh_send, 0);
+	wake_up_all(&task->wqh_recv, 0);
+
+	/*
+	 * The thread cannot have a pager waiting for it
+	 * since we ought to be the pager.
+	 */
+	BUG_ON(task->wqh_pager.sleepers > 0);
+
+	/* Clear the task's tcb */
+	arch_clear_thread(task);
+
+	return 0;
+}
+
 int thread_destroy(struct task_ids *ids)
 {
 	struct ktcb *task;
@@ -292,6 +333,10 @@ int sys_thread_control(syscall_context_t *regs)
 		break;
 	case THREAD_DESTROY:
 		ret = thread_destroy(ids);
+		break;
+	case THREAD_RECYCLE:
+		ret = thread_recycle(ids);
+		break;
 	default:
 		ret = -EINVAL;
 	}