如何正确唤醒中断处理程序中的进程 [英] How correctly wake up process inside interrupt handlers

问题描述

简而言之，在 read 方法中，我检查变量是否为0，如果是，则将当前进程置于睡眠状态:

Briefly, in a read method i check if a variable is 0 and if it's i put the current process to sleep:

static ssize_t soc2e_read(struct file *filp, char __user *buf,
                          size_t count, loff_t * ppos)
{
    ...
    struct soc2e_dev *soc2e = (struct soc2e_dev *)filp->private_data;

    if (soc2e->bytes == 0)
    {
        if (wait_event_interruptible(soc2e->wlist, (soc2e->bytes > 0)))
            return -ERESTARTSYS;
    }
    ...
 }

我必须在中断处理程序中唤醒进程:

I must wake up the process in an interrupt handler:

static irqreturn_t soc2e_irq_handler(int irq, void *dev)
{
   ...
   struct soc2e_dev *soc2e = dev;
   ...
   soc2e->bytes += read_bytes;

   wake_up_interruptible(&soc2e->wlist);
   return IRQ_HANDLED;
}

我认为(并已验证)这可能是原子性问题.如果中断发生在 read 方法中的 if(soc2e-> bytes == 0)和 wait_event_interruptible 的调用之间.也许直到下一个中​​断才会唤醒该进程.解决此问题的最佳方法是什么?

I think (and also verified) that here could be a problem of atomicity. What happen if interrupt comes between if (soc2e->bytes == 0) in read method and the call to wait_event_interruptible. Maybe the process won't be waked up until next interrupt. What is the best way to resolve this issue?

推荐答案

wait_event_interruptible 宏在避免描述种族方面已经非常小心了.实际上，您不需要对 bytes 成员进行初始检查-您只需在您的 read 方法中编写:

The wait_event_interruptible macro is already pretty careful about avoiding the race you describe. In fact, you don't need the initial check of your bytes member -- you could just write in your read method:

  if (wait_event_interruptible(soc2e->wlist, soc2e->bytes > 0))
          return -ERESTARTSYS;

因为 wait_event_interruptible()如果条件为真(或者在进入睡眠状态时变为真)，则实际上不会进入睡眠状态.

because wait_event_interruptible() will not actually go to sleep if the condition is true (or becomes true while it's in the middle of going to sleep).

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