feat(sched): add observable kernel thread exit

docs/agents/tasks/04-time-scheduler.md

@@ -152,9 +152,10 @@
 - 已把 `kernel_thread_create()` 中的线程 id 分配和 run queue 入队纳入 interrupt-safe lock 保护。
 - 已建立 `sched_irq_exit()`，timer IRQ 只设置 `need_resched`，trap 的 IRQ 返回边界统一消费调度请求。
 - 已建立最小 DEAD 线程回收路径，调度前会释放非当前 DEAD 线程的内核栈和线程对象。
+- 已建立统一 `kernel_thread_exit()`/`sched_thread_exit()`，线程入口返回和显式退出都会进入明确退出路径，再由调度安全边界回收非当前 DEAD 线程。
 - 已在调度私有头中加入 thread state helper，调度核心、线程退出和 wait queue 路径不再直接散写主要状态转换。
 - 已把调度代码按职责拆分为 `core.c`、`thread.c`、`wait.c`、`idle.c` 和私有 `sched.h`，并把当前阶段自测/演示线程移到 `kernel/selftest/sched.c`。
-- `scripts/check.sh` 已验证 `timer initialized`、`timer tick=1/2/3`、`scheduler initialized`、`kernel thread selftest ok`、timer 驱动线程轮转、`sched_sleep()`、wait queue wakeup、条件等待和超时等待。
+- `scripts/check.sh` 已验证 `timer initialized`、`timer tick=1/2/3`、`scheduler initialized`、`kernel thread selftest ok`、timer 驱动线程轮转、`sched_sleep()`、wait queue wakeup、条件等待、超时等待、线程返回退出、显式退出和 DEAD 线程回收。
 
 后续扩展：
 
@@ -181,7 +182,7 @@
 ### D. thread lifecycle
 
 - 为线程退出增加更完整的生命周期状态、引用规则和最终释放约束。
-- 补充“当前线程不能释放自身内核栈”的文档和自测。
+- 继续补充“当前线程不能释放自身内核栈”的更严格断言和未来 join/wait 语义。
 - 为未来 `kthread_stop()`、join/wait 和进程退出保留接口空间。
 - 回收路径需要覆盖等待队列残留、run queue 残留和 timer sleep 残留。
 

include/tianole/sched.h

@@ -41,6 +41,7 @@ struct thread {
 void sched_init(void);
 struct thread *kernel_thread_create(
 	const char *name, kernel_thread_entry_t entry, void *arg);
+void kernel_thread_exit(void) __attribute__((noreturn));
 void sched_start(void) __attribute__((noreturn));
 void sched_tick(uint64_t tick);
 void sched_irq_exit(void);

kernel/sched/sched.h

@@ -74,6 +74,7 @@ static inline void thread_set_dead(struct thread *thread)
 
 void enqueue_thread(struct thread *thread);
 void sched_reap_dead_threads(void);
+void sched_thread_exit(void) __attribute__((noreturn));
 void sched_selftest(void);
 int sched_idle_create(void);
 void sched_demo_start(void) __attribute__((noreturn));

kernel/sched/thread.c

@@ -98,6 +98,9 @@ struct thread *kernel_thread_create(
 
 static void release_thread(struct thread *thread)
 {
+	early_log_puts("thread reaped ");
+	early_log_puts(thread->name);
+	early_log_puts("\n");
 	kfree(thread->stack_base);
 	kfree(thread);
 }
@@ -106,7 +109,10 @@ void sched_reap_dead_threads(void)
 {
 	struct thread *prev = 0;
 	struct thread *thread = run_queue_head;
+	struct thread *reap_list = 0;
+	uint64_t flags;
 
+	spin_lock_irqsave(&scheduler_lock, &flags);
 	while (thread != 0) {
 		struct thread *next = thread->next;
 
@@ -121,13 +127,41 @@ void sched_reap_dead_threads(void)
 				run_queue_tail = prev;
 			}
 
-			release_thread(thread);
+			thread->next = reap_list;
+			reap_list = thread;
 		} else {
 			prev = thread;
 		}
 
 		thread = next;
 	}
+	spin_unlock_irqrestore(&scheduler_lock, flags);
+
+	while (reap_list != 0) {
+		struct thread *next = reap_list->next;
+
+		reap_list->next = 0;
+		release_thread(reap_list);
+		reap_list = next;
+	}
+}
+
+void sched_thread_exit(void)
+{
+	if (current_thread == 0) {
+		panic("thread exit without current thread");
+	}
+
+	thread_set_dead(current_thread);
+
+	for (;;) {
+		sched_yield();
+	}
+}
+
+void kernel_thread_exit(void)
+{
+	sched_thread_exit();
 }
 
 static void thread_trampoline(void)
@@ -139,9 +173,5 @@ static void thread_trampoline(void)
 	}
 
 	thread->entry(thread->arg);
-	thread_set_dead(thread);
-
-	for (;;) {
-		sched_yield();
-	}
+	kernel_thread_exit();
 }

kernel/selftest/sched.c

@@ -134,6 +134,21 @@ static void timeout_wait_demo_waiter(void *arg)
 	early_log_puts("timeout waiter timed out\n");
 }
 
+static void return_exit_demo_thread(void *arg)
+{
+	(void)arg;
+
+	early_log_puts("return exit thread returning\n");
+}
+
+static void explicit_exit_demo_thread(void *arg)
+{
+	(void)arg;
+
+	early_log_puts("explicit exit thread exiting\n");
+	kernel_thread_exit();
+}
+
 void sched_demo_start(void)
 {
 	struct thread *first = kernel_thread_create(
@@ -150,10 +165,14 @@ void sched_demo_start(void)
 		"condition-waker", condition_wait_demo_waker, 0);
 	struct thread *timeout_waiter = kernel_thread_create(
 		"timeout-waiter", timeout_wait_demo_waiter, 0);
+	struct thread *return_exit =
+		kernel_thread_create("return-exit", return_exit_demo_thread, 0);
+	struct thread *explicit_exit = kernel_thread_create(
+		"explicit-exit", explicit_exit_demo_thread, 0);
 
 	if (first == 0 || second == 0 || waiter == 0 || waker == 0 ||
 		condition_waiter == 0 || condition_waker == 0 ||
-		timeout_waiter == 0) {
+		timeout_waiter == 0 || return_exit == 0 || explicit_exit == 0) {
 		panic("scheduler demo thread creation failed");
 	}
 

scripts/checks/boot.sh

@@ -34,6 +34,12 @@ check_lines build/debug.log \
 	"condition waiter sleeping" \
 	"condition waker sleeping" \
 	"timeout waiter sleeping" \
+	"return exit thread returning" \
+	"explicit exit thread exiting" \
+	"thread reaped worker-a" \
+	"thread reaped worker-b" \
+	"thread reaped return-exit" \
+	"thread reaped explicit-exit" \
 	"preempt thread 1 step=2" \
 	"preempt thread 2 step=2" \
 	"timeout waiter timed out" \
@@ -71,6 +77,12 @@ check_lines build/serial.log \
 	"condition waiter sleeping" \
 	"condition waker sleeping" \
 	"timeout waiter sleeping" \
+	"return exit thread returning" \
+	"explicit exit thread exiting" \
+	"thread reaped worker-a" \
+	"thread reaped worker-b" \
+	"thread reaped return-exit" \
+	"thread reaped explicit-exit" \
 	"preempt thread 1 step=2" \
 	"preempt thread 2 step=2" \
 	"timeout waiter timed out" \