Mixed changes

- Added automatic utcb map/prefaulting of forked tasks for fs0
  so that it does not need to explicitly request those tasks from mm0.
  Eliminating fs0 requests to mm0 reduce deadlock possibilities.

- Replaced kmalloc with a public malloc implementation because of a bug in kmalloc.
- Fixed a kfree bug. default_release_pages was trying to free page_array pages.

tasks/mm0/src/task.c

@@ -512,6 +512,27 @@ void init_pm(struct initdata *initdata)
 	start_boot_tasks(initdata);
 }
 
+/* Maps and prefaults the utcb of a task into another task */
+void task_map_prefault_utcb(struct tcb *mapper, struct tcb *owner)
+{
+	BUG_ON(!owner->utcb);
+
+	/*
+	 * First internally map the tcb as a shm area. We use
+	 * such posix semantics on purpose to have a unified
+	 * way of doing similar operations.
+	 */
+	BUG_ON(IS_ERR(shmat_shmget_internal(mapper,
+					    (key_t)owner->utcb,
+					    owner->utcb)));
+
+	/* Prefault the owner's utcb to mapper's address space */
+	for (int i = 0; i < __pfn(DEFAULT_UTCB_SIZE); i++)
+		prefault_page(mapper, (unsigned long)owner->utcb +
+			      __pfn_to_addr(i), VM_READ | VM_WRITE);
+
+}
+
 /*
  * During its initialisation FS0 wants to learn how many boot tasks
  * are running, and their tids, which includes itself. This function
@@ -535,7 +556,7 @@ int send_task_data(l4id_t requester)
 	BUG_ON(!vfs->utcb);
 
 	/* Attach mm0 to vfs's utcb segment just like a normal task */
-	BUG_ON(IS_ERR(shmat_shmget_internal((key_t)vfs->utcb, vfs->utcb)));
+	BUG_ON(IS_ERR(shmat_shmget_internal(self, (key_t)vfs->utcb, vfs->utcb)));
 
 	/* Prefault those pages to self. */
 	for (int i = 0; i < __pfn(DEFAULT_UTCB_SIZE); i++)