RE: [PATCH v2] exec: make de_thread() freezable

["Chanho Min" <chanho.min@lge.com>]

> > > It's been some time since I have looked into this code so bear with
me.
> > > One thing is not really clear to me. Why does it help to exclude this
> > > particular task from the freezer
> >
> > we don't exclude it,
> >
> > > when it is not sleeping in the freezer.
> >
> > Yes, it is not sleeping in __refrigerator(), but it does
> >
> > 	schedule();
> > 	freezer_count();
> >
> > so it will enter __refrigerator() right after wakeup. If it won't be
> woken
> > up we do not care, we can consider it "frozen".
> 
> Right, but this is just silencing the freezing code to exclude this
> task, right?
> 
> > > I can see how other threads need to be zapped and TASK_WAKEKILL
> doesn't
> > > do that but shouldn't we fix that instead?
> >
> > Not sure I understand, but unlikely we can (or want) to make
> __refrigerator()
> > killable.
> 
> Why would that be a problem. If the kill is fatal then why to keep the
> killed task in the fridge?
> 

Is it  different between 'the killed task is frozen' and '__refrigerator()
is killable'?
From a general '__refrigerator()' implementation point of view I know that
it should not be killable.

> > Otherwise, how can we fix that?
> 
> We can mark all threads PF_NOFREEZE and wake them up. This would require
> some more changes of course but wouldn't that be a more appropriate
> solution? Do we want to block exec for ever just because some threads
> are in the fridge?
> 

IMHO, It seems to be difficult and buggy to control with PF_NOFREEZE.
Because,
The sub-thread can freeze and receive SIG_KILL before the marking of
PF_NOFREEZE
and it should be freezable in other cases. I don't understand why it isn't
appropriate
for exec to block. The exec can freeze. When tasks are thawed, the killed
sub-thread
will die and wake de_thread(). The exec will continue to work from resume.

Chanho