Re: freeze_processes questions

Rafael J. Wysocki
2005-04-05T18:02:29Z

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Hi,

On Tuesday, 5 of April 2005 11:53, Rafael J. Wysocki wrote:
> On Tuesday, 5 of April 2005 11:27, Pavel Machek wrote:
> > Hi!
> > >
> > > I have two questions regarding freeze_processes():
> > >
> > > 1) Shouldn't we take the TASK_UNINTERRUPTIBLE state into consideration? Now
> > > we will fail if a process is sleeping when we try to freeze it.
> >
> > We can't allow processes to sleep at arbitrary places. Therefore we
> > send UNINTERRUPTIBLE task a signal, and hope it can get into
> > refrigerator in time.
>
> Hm, AFAIK we can't kill an UNINTERRUPTIBLE process, can we? Which means that
> we can't deliver a signal to it too ...

Well, the problem is that signal_wake_up() is not sufficient to make
an uninterruptible task get the signal. It only sets TIF_SIGPENDING for the
task, which is not quite good, IMHO (when the task finally wakes up,
it gets the "signal" and enters refrigerator(), because it has PF_FREEZE set,
and stays there forever, as there's nothing that could clear PF_FROZEN for
it).

I think it may be fixed in one of the two ways:

1) We can treat uninterruptible tasks as non-freezable (in analogy to stopped
tasks) - if all of the other tasks are frozen, nothing can wake up an uninterruptible
task, so this seems to be a safe approach.

2) We can try to force uninterruptible tasks to get their "signals" anyway using
wake_up_state() directly on them (which I don't like as much).

Greets,
Rafael

--
- Would you tell me, please, which way I ought to go from here?
- That depends a good deal on where you want to get to.
-- Lewis Carroll "Alice's Adventures in Wonderland"