On Saturday, 12 May 2007 18:58, Oleg Nesterov wrote:
> On 05/12, Rafael J. Wysocki wrote:
> >
> > Ah, I see. We spawn a kernel thread from a code path that belongs to a
> > user space task and we need to call deamonize() to make it become a
> > 'real' kernel thread.
> >
> > Still, this means that is_user_space() may return 'true' for this thread
> > before it calls daemonize() and then the scenario described by me in the
> > previous message may occur. It seems.
>
> Yes sure. Probably not so bad in practice. Most likely this fresh thread
> is not "important" and could be freezed, I dunno.
I don't know too, and that's why I'd like to prevent this from happening.
> > It's in freezer-fix-pf_nofreeze-vs-freezeable-race.patch (appended for
> > convenience, white space may be broken).
> >
> > ---
> > --- a/include/linux/freezer.h~freezer-fix-pf_nofreeze-vs-freezeable-race
> > +++ a/include/linux/freezer.h
> > @@ -63,8 +63,10 @@ static inline int thaw_process(struct ta
> > */
> > static inline void frozen_process(struct task_struct *p)
> > {
> > - p->flags |= PF_FROZEN;
> > - wmb();
> > + if (!unlikely(p->flags & PF_NOFREEZE)) {
> > + p->flags |= PF_FROZEN;
> > + wmb();
> > + }
> > clear_tsk_thread_flag(p, TIF_FREEZE);
> > }
>
> This is OK if a kernel thread does try_to_freeze() eventually.
>
> But what if it does not, because it marks itself as PF_NOFREEZE?
> This means it may run with signal_pending() forever. That is why
> I think we should clear TIF_FREEZE when we set PF_NOFREEZE.
Yes, we should.
Greetings,
Rafael
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