On Sat, Feb 03, 2007 at 11:27:24PM +0100, Rafael J. Wysocki wrote:
> On Saturday, 3 February 2007 01:01, Pavel Machek wrote:
> > Hi!
> >
> > > > > > static int _cpu_down(unsigned int cpu)
> > > > > > {
> > > > > > int err;
> > > > > > struct task_struct *p;
> > > > > > cpumask_t old_allowed, tmp;
> > > > > >
> > > > > > if (num_online_cpus() == 1)
> > > > > > return -EBUSY;
> > > > > >
> > > > > > if (!cpu_online(cpu))
> > > > > > return -EINVAL;
> > > > > >
> > > > > > if (freeze_processes()) {
> > > > > > err = -EBUSY;
> > > > > > goto out_freeze_notify_failed;
> > > > > > }
> > > > > > err = raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE,
> > > > > > (void *)(long)cpu);
> > > > >
> > > > > yeah. This all looks so nice that i almost cannot believe it's true :-)
> > > >
> > > > Well, it turns out that maybe it is in fact untrue. :-/
> > > >
> > > > I need to look at all uses of PF_NOFREEZE -- as I understand the
> > > > code, processes marked PF_NOFREEZE will continue running, potentially
> > > > interfering with the hotplug operation. :-(
> > > >
> > > > I will pass my findings on to this list.
> > >
> > > Well, I did it some time ago, although not very thoroughly.
> > >
> > > AFAICS there are not so many, but one that stands out is the worker threads.
> > > We needed two of them to actually go to sleep, so now it's possible to create
> > > a "freezeable workqueue" the worker thread of which will not set PF_NOFREEZE,
> > > but currently this is only used by XFS.
> >
> > We should slowly move as workqueues to freezeable ones... Having too
> > much stuff NOFREEZE is evil, even for swsusp.
>
> On the other hand, some of the workqueues may be necessary for saving the image
> (still, I have no examples ;-)).
In any case, getting CPU hotplug working is probably first priority.
That said, I am testing a patch that (hopefully) gets rid of the
RCU-boost and rcutorture NOFREEZE tasks. Every little bit will help.
Thanx, Paul
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