Re: [PATCH -mm 1/2]: PM: Fix handling of stopped tasks

["Rafael J. Wysocki" <rjw@sisk.pl>]

Hi,

On Tuesday, 5 December 2006 15:12, Pavel Machek wrote:
> Hi!
> 
> > > > Actually, what do you think about this patch? It removes special
> > > > handling of TASK_TRACED, and should do the trick, too...
> > > 
> > > I was surprised, but the patch seems to work okay. Can you replace
> > > your 1/2 with this one, and see what breaks?
> > 
> > I don't think anything will _visibly_ break, because (1) even if the traced
> > task has TIF_SIGPENDING set unnecessarily, it will just notice there is no
> > real signal to handle and continue and 
> 
> We are generating spurious wakeups, but as you noticed, that should be
> okay.

So we can move the check to freezeable().  Fine.

> >(2) the race between the delivery of
> > the continuation signal and the freezer is damn hard to trigger (still I think
> > I can wirte some artificial code that would trigger this, although it would
> > involve a kernel thread sending SIGCONT to a user space process - provided
> > it's permissible ;-)).
> 
> It is not really permissible, but I do not see how it would hurt...
> 
> With that patch, we put TASK_STOPPED tasks into refrigerator, along
> with everyone else. SIGCONT is *not* going to help them out of
> refrigerator.
> 
> We also ignore TASK_STOPPED now, so we'll not proceed until all
> stopped tasks are in refrigerator.
> 
> Now... I'm not 100% sure I got the ptrace() cases right (and did not
> test that)... but TASK_STOPPED cases look pretty trivial to me now.

Please note that currently (and with your patch) freezeable() returns 0 for
TASK_STOPPED, so we don't set PF_FREEZE for them and my patch changes
_exactly_ that and adds some minor (optional) modifications to the error
paths.

Greetings,
Rafael


-- 
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