Question

如signal（7）手册页所述，

   Interruption of system calls and library functions by signal handlers
       If a signal handler is invoked while a system call or library function call is blocked, then either:

       * the call is automatically restarted after the signal handler returns; or

       * the call fails with the error EINTR.

       Which  of  these  two behaviors occurs depends on the interface and whether or not the signal handler was established using the SA_RESTART flag (see sigaction(2)).  The details vary across UNIX systems; below, the details for
       Linux.

       If a blocked call to one of the following interfaces is interrupted by a signal handler, then the call will be automatically restarted after the signal handler returns if the SA_RESTART flag was used; otherwise the call  will
       fail with the error EINTR:

           * read(2),  readv(2),  write(2), writev(2), and ioctl(2) calls on "slow" devices.  A "slow" device is one where the I/O call may block for an indefinite time, for example, a terminal, pipe, or socket.  If an I/O call on a
             slow device has already transferred some data by the time it is interrupted by a signal handler, then the call will return a success status (normally, the number of bytes transferred).  Note that a (local) disk is not a
             slow device according to this definition; I/O operations on disk devices are not interrupted by signals.

如上所述，信号处理程序中断了对以下接口之一（读，写）的阻塞调用，如果使用SA_RESTART标志，则信号处理程序返回后，该调用将自动重新启动，这意味着如果阻塞了读写系统调用，则进程必须处于TASK_INTERRUPTIBLE状态。

但是当我试图找出使进程处于TASK_UNINTERRUPTIBLE状态的阻塞系统调用时，我发现了https://unix.stackexchange.com/questions/62697/why-is-i-o-uninterruptible和Why doing I/O in Linux is uninterruptible?，并且在这两个地方都提到了阻塞的I / O调用（读，写）将一个进程放入TASK_UNINTERRUPTIBLE。

这里也提到了它：https://access.redhat.com/sites/default/files/attachments/processstates_20120831.pdf

The Uninterruptible state is mostly used by device drivers waiting for disk or network I/O. When the process
is sleeping uninterruptibly, signals accumulated during the sleep are noticed when the process returns from
the system call or trap. In Linux systems. the command ps -l uses the letter D in the state field (S) to
indicate that the process is in an Uninterruptible sleep state. In that case, the process state flag is set as
follows:
p->state = TASK_UNINTERRUPTABLE
LEARN MORE: Read more about D states in the Red Hat Knowledgebase:
https://access.redhat.com/knowledge/solutions/59989/

有点令人困惑。

我还想知道其他阻塞的系统调用，这些调用会使进程进入TASK_UNINTERRUPTIBLE状态。

Answer 1

对于read(2)或write(2)家族的系统调用，睡眠类型取决于所访问文件的类型。在您引用的文档中，“慢速”设备是指read/write可以中断睡眠的设备，而“快速”设备是指可以不间断睡眠的设备（“磁盘等待”的不间断睡眠状态称为D ”，因为最初read/write在磁盘文件上是这种睡眠的最常见原因。

请注意，“阻止”在技术上仅指可中断的睡眠。

几乎所有系统调用都可以进入不间断的睡眠，因为（在其他情况下）这可能在进程需要获取保护内部内核资源的锁时发生。通常，这种不间断的睡眠是如此短暂，以至于您不会注意到它。

读/写阻止的系统调用是否将进程置于TASK_UNINTERRUPTIBLE或TASK_INTERRUPTIBLE状态？

1 个答案: