Re: [linux-pm] [RFC][PATCH -mm 1/5] PM: Make freeze_processes SMP-safe

Rafael J. Wysocki
2006-12-01T19:57:01Z

On Friday, 1 December 2006 15:56, Alan Stern wrote:
> On Thu, 30 Nov 2006, Rafael J. Wysocki wrote:
>
> > > Here's what I mean. usb-storage's kernel thread is unfreezable, because
> > > it might be needed for reading or writing a memory image to a swap region.
> > > If there's an I/O error then usb-storage will try to issue a USB port
> > > reset, for which it needs to acquire the USB device's lock.
> > >
> > > Now various other tasks may acquire that lock, and they may even stop
> > > while holding it. However they should never get frozen while holding the
> > > lock -- which means they shouldn't get frozen at arbitrary times merely
> > > because they are stopped. They are careful to call try_to_freeze() only
> > > at times when they don't hold any locks.
> >
> > This means they are kernel threads, so they won't be entering
> > get_signal_to_deliver(), will they?
>
> Some of them are kernel threads and some of them are user threads. Only
> the kernel threads call try_to_freeze().
>
> > If they don't enter get_signal_to_deliver(), they can only be frozen where
> > they explicitly call try_to_freeze().
>
> What about the user threads?

We send fake signals to them, so they enter get_signal_to_deliver() and they
call try_to_freeze() from there.

Greetings,
Rafael

--
You never change things by fighting the existing reality.
R. Buckminster Fuller