[kernel] 被动挂起的线程，无法处理信号

[weidongshan]

拉取/合并请求描述：(PR description)

[
如果一个线程不是调用rt_thread_delay等函数主动进入挂起状态，不是在rt_schedule函数中放弃运行，
那么其他线程给它发信号时，它是不会执行信号处理函数的。
这个Bug的原因在于：在_signal_deliver函数中，发现目标线程处于挂起状态时，
只做了3件事：把它唤醒、设置线程状态为RT_THREAD_STAT_SIGNAL_PENDING、调用rt_schedule。
我们期望目标线程被唤醒后，从rt_schedule继续运行时，发现线程状态为RT_THREAD_STAT_SIGNAL_PENDING时调用信号处理函数。
但是，目标线程挂起时，不一定是在rt_schedule函数中放弃运行，比如它可能是被其他线程调用rt_thread_suspend挂起的。
这时候，目标线程不会执行信号处理函数。

为什么提交这份PR (why to submit this PR)

你的解决方案是什么 (what is your solution)

修改了src/signal.c，即使目标线程处于挂起状态，也是去修改它的栈。

在什么测试环境下测试通过 (what is the test environment)

可以如下复现这个Bug：创建2个线程，让thread2挂起thread1，然后给thread1发信号。示例代码如下：
`static void thread1_entry(void *parameter)
{
const char *thread_name = parameter;
int cnt = 0;

/* 打印线程的信息 */
rt_kprintf("%s run ...\r\n", thread_name);

/* 安装信号,自定义处理函数 */
rt_signal_install(SIGUSR1, thread1_signal_handler);

/* 解除阻塞 */
rt_signal_unmask(SIGUSR1);

while(1)
{		
    rt_kprintf("%s %d\r\n", thread_name, cnt++);
}

}

/* 线程2的入口函数 */
static void thread2_entry(void *parameter)
{
const char *thread_name = parameter;
int cnt = 0;

/* 打印线程的信息 */
rt_kprintf("%s run ...\r\n", thread_name);

rt_thread_mdelay(100);	

while(1)
{		
    rt_kprintf("%s %d\r\n", thread_name, cnt++);
    rt_thread_suspend(thread1);    
    rt_thread_kill(thread1, SIGUSR1); //向线程1发送信号SIGUSR1
}

}`

]

当前拉取/合并请求的状态 Intent for your PR

必须选择一项 Choose one (Mandatory):

• 本拉取/合并请求是一个草稿版本 This PR is for a code-review and is intended to get feedback
• 本拉取/合并请求是一个成熟版本 This PR is mature, and ready to be integrated into the repo

代码质量 Code Quality：

我在这个拉取/合并请求中已经考虑了 As part of this pull request, I've considered the following:

• 已经仔细查看过代码改动的对比 Already check the difference between PR and old code
• 代码风格正确，包括缩进空格，命名及其他风格 Style guide is adhered to, including spacing, naming and other styles
• 没有垃圾代码，代码尽量精简，不包含#if 0代码，不包含已经被注释了的代码 All redundant code is removed and cleaned up
• 所有变更均有原因及合理的，并且不会影响到其他软件组件代码或BSP All modifications are justified and not affect other components or BSP
• 对难懂代码均提供对应的注释 I've commented appropriately where code is tricky
• 代码是高质量的 Code in this PR is of high quality
• 已经使用formatting等源码格式化工具确保格式符合RT-Thread代码规范 This PR complies with RT-Thread code specification

[CLAassistant]

All committers have signed the CLA.

[polarvid]

有个题外话。导致这个问题的直接原因 —— 调用 rt_thread_suspend() 挂起其它线程。从 API 的使用场景来说应该是滥用了吧？这个实现可能最初假定就是在 rt_schedule() 恢复运行时去做这些逻辑。因此我有点好奇这种不是主动挂起的场景是否具有合理性呢？

rt-thread/src/thread.c

Lines 966 to 982 in 307e9e5

	/**
	* @brief This function will suspend the specified thread and change it to suspend state.
	*
	* @note This function ONLY can suspend current thread itself.
	* rt_thread_suspend(rt_thread_self());
	*
	* Do not use the rt_thread_suspend to suspend other threads. You have no way of knowing what code a
	* thread is executing when you suspend it. If you suspend a thread while sharing a resouce with
	* other threads and occupying this resouce, starvation can occur very easily.
	*
	* @param thread the thread to be suspended.
	* @param suspend_flag status flag of the thread to be suspended.
	*
	* @return Return the operation status. If the return value is RT_EOK, the function is successfully executed.
	* If the return value is any other values, it means this operation failed.
	*/
	rt_err_t rt_thread_suspend_with_flag(rt_thread_t thread, int suspend_flag)

Do not use the rt_thread_suspend to suspend other threads.

[weidongshan]

有个题外话。导致这个问题的直接原因 —— 调用 rt_thread_suspend() 挂起其它线程。从 API 的使用场景来说应该是滥用了吧？这个实现可能最初假定就是在 rt_schedule() 恢复运行时去做这些逻辑。因此我有点好奇这种不是主动挂起的场景是否具有合理性呢？

rt-thread/src/thread.c

Lines 966 to 982 in 307e9e5

	/**
	* @brief This function will suspend the specified thread and change it to suspend state.
	*
	* @note This function ONLY can suspend current thread itself.
	* rt_thread_suspend(rt_thread_self());
	*
	* Do not use the rt_thread_suspend to suspend other threads. You have no way of knowing what code a
	* thread is executing when you suspend it. If you suspend a thread while sharing a resouce with
	* other threads and occupying this resouce, starvation can occur very easily.
	*
	* @param thread the thread to be suspended.
	* @param suspend_flag status flag of the thread to be suspended.
	*
	* @return Return the operation status. If the return value is RT_EOK, the function is successfully executed.
	* If the return value is any other values, it means this operation failed.
	*/
	rt_err_t rt_thread_suspend_with_flag(rt_thread_t thread, int suspend_flag)

Do not use the rt_thread_suspend to suspend other threads.

使用rt_thread_suspend 暂停其他线程确实不是一个好的编程习惯，因为你不知道别的线程暂停时需要做什么额外的工作。比如要暂停一个音乐播放器，你使用rt_thread_suspend 的话，也许它会发出一个恒定不变的声音（比如使用PWM播放音乐时就会这样）。
这里提到的信号bug，也会出现在“主动阻塞的场景”里，比如thread1调用rt_thread_delay，然后thread2给thread1发信号：会唤醒thread1，但是thread1并不会执行信号函数。