On Wed, 31 Jan 2007, Oliver Neukum wrote:
> Am Mittwoch, 31. Januar 2007 16:54 schrieb Alan Stern:
> > On Wed, 31 Jan 2007, Pavel Machek wrote:
>
> > > "cease IO"? No, I believe it is enough not to start new I/O. Userspace
> > > is frozen at that point, it can't ask you to do I/O.
> >
> > There may be I/O requests sitting in a queue, already submitted by
> > userspace. The suspend method should wait for existing I/O to complete
> > and stop processing new entries from the queue.
>
> As far as I understand it now, a frozen process will be in the refrigerator.
> Thus it cannot be blocking somewhere else in kernel space. Yet we cannot
> be sure there's no queued IO, as theres aio.
Or the driver may maintain its own I/O queue, like the HID driver does.
> > > > On resume():
> > > >
> > > > 1. Don't worry about TASK_UNINTERRUPTIBLE
> > > > 2. Do not restart IO that may call wake_up_interruptible()
> > > >
> > > > When do we restart such IO?
> > >
> > > We reuse signal handling code to do that for us. It is same situation
> > > as when someone signals task doing I/O.
> >
> > Again you misunderstood the question. The driver must start queued I/O
> > when its resume() method is called. It should then be okay for the driver
> > to call wake_up_interruptible(), even before tasks are unfrozen.
>
> Isn't there some code in usbfs that'll do homegrown aio and deliver a
> signal to a process if io is completed?
That's right. There's also code in the hub driver to call wake_up() on
the khubd thread when certain I/O operations complete; nevertheless khubd
_should_ remain frozen along with all the other tasks.
Alan Stern
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