Re: Lots of bugs with current->state = TASK_*INTERRUPTIBLE

Frederic Weisbecker
2010-01-21T10:53:14Z

On Thu, Jan 21, 2010 at 11:47:41AM +0100, Julia Lawall wrote:
> What about something like the following (drivers/macintosh/adb.c):
>
> add_wait_queue(&state->wait_queue, &wait);
> current->state = TASK_INTERRUPTIBLE;
>
> for (;;) {
> req = state->completed;
> if (req != NULL)
> state->completed = req->next;
> else if (atomic_read(&state->n_pending) = 0)
> ret = -EIO;
> if (req != NULL || ret != 0)
> break;
>
> if (file->f_flags & O_NONBLOCK) {
> ret = -EAGAIN;
> break;
> }
> if (signal_pending(current)) {
> ret = -ERESTARTSYS;
> break;
> }
> spin_unlock_irqrestore(&state->lock, flags);
> schedule();
> spin_lock_irqsave(&state->lock, flags);
> }
>
> current->state = TASK_RUNNING;
> remove_wait_queue(&state->wait_queue, &wait);
>
> There is a call to schedule eventually after the first current->state
> assignment, but it is not right after.

Looks fine as spin_unlock includes a memory barrier, IIRC.