Re: Software suspend testing in 2.6.0-test1

[Peter Osterlund <petero2@telia.com>]

Pavel Machek <pavel@ucw.cz> writes:

> > @@ -214,9 +218,12 @@
> >  		read_lock(&tasklist_lock);
> >  		do_each_thread(g, p) {
> >  			unsigned long flags;
> > -			INTERESTING(p);
> > +			if (!interesting_process(p))
> > +				continue;
> >  			if (p->flags & PF_FROZEN)
> >  				continue;
> > +			if (p->state == TASK_STOPPED)
> > +				continue;
> >  
> >  			/* FIXME: smp problem here: we may not access other process' flags
> >  			   without locking */
> 
> No need to handle TASK_STOPPED tasks, as they are "frozen" already. Ok.

If the process was stopped before swsusp was invoked, the process will
never reach refrigerator() and therefore never set the PF_FROZEN
flag. Without the test for TASK_STOPPED, swsusp gives up and claims
that it can't stop all processes.

> >  	read_lock(&tasklist_lock);
> >  	do_each_thread(g, p) {
> > -		INTERESTING(p);
> > -		
> > -		if (p->flags & PF_FROZEN) p->flags &= ~PF_FROZEN;
> > -		else
> > -			printk(KERN_INFO " Strange, %s not stopped\n", p->comm );
> > -		wake_up_process(p);
> > +		if (!interesting_process(p))
> > +			continue;
> > +
> > +		p->flags &= ~PF_FREEZE;
> > +		if (p->flags & PF_FROZEN) {
> > +			p->flags &= ~PF_FROZEN;
> > +			wake_up_process(p);
> > +		} else
> > +			
> But why do you touch PF_FROZEN here? Refrigerator should do that.
> And wake_up_process should not be needed...
> If it is in refrigerator, it polls PF_FREEZE...

Note that the old code always called wake_up_process(), which is
necessary to make the process run one more iteration in refrigerator()
and relize that it is time to unfreeze.

The patch changes things so that wake_up_process() is NOT called if
the process is stopped at some other place than in refrigerator().
This ensures that processes that were stopped before we invoked swsusp
are still stopped after resume.

I manually clear PF_FREEZE here in an attempt to handle a race
condition, but I realize I need to understand more of the scheduler
and signal code before I know for sure if this is necessary and/or
sufficient.

-- 
Peter Osterlund - petero2@telia.com
http://w1.894.telia.com/~u89404340