Re: [PATCH] fix refrigerator() vs thaw_process() race

[Pavel Machek]

Hi!

> > > refrigerator() can miss a wakeup, "wait event" loop needs a proper memory
> > > ordering.
> > > 
> > > Signed-off-by: Oleg Nesterov <[EMAIL PROTECTED]>
> > > 
> > > --- WQ/kernel/power/process.c~WAKE        2007-02-18 22:56:49.000000000 
> > > +0300
> > > +++ WQ/kernel/power/process.c     2007-02-19 01:04:26.000000000 +0300
> > > @@ -46,8 +46,10 @@ void refrigerator(void)
> > >   recalc_sigpending(); /* We sent fake signal, clean it up */
> > >   spin_unlock_irq(&current->sighand->siglock);
> > >  
> > > -         current->state = TASK_UNINTERRUPTIBLE;
> > > +         set_current_state(TASK_UNINTERRUPTIBLE);
> > 
> > 
> > Looks okay to me... but this one liner would be exactly as effective,
> > right?
> 
> I think no, with this one liner we have
> 
>       while (frozen(current)) {
>               // ------ WINDOW ------------
>               set_current_state(TASK_UNINTERRUPTIBLE);
>               schedule();
>       }
> 
> What if thaw_process() happens in the window above?
> 
> We need the barrier exactly because LOAD (check condition) should not
> come before STORE (set task->state).

Aha, ok :-). You already have my ACK ;-).
                                                                        Pavel

-- 
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